Cassini Encounters Enceladus Background and the Discovery of
a South Polar Hot SpotSpencer et al 10 March 2006 Science 311 1401
Presented by Shannon GuilesAstronomy 671April 10 2006
Image Credit NASAJPLGSFC
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeCould frame thy fearful symmetry
Cassini
Cassini entered orbit around Saturn on 1 July
2004 and it will orbit there for four years
Cassini has 12 instruments while the Hyugens probe
(which descended to Titans surface in January
2005) had 6
Cassini had three close flybys of Enceladus between Feb amp July
2005 One more scheduled for Spring
2008Credit NASA
Credit NASA
CIRS
Cassini Composite Infrared Spectrometer
Reference Flazar et al (2004)
In what distant deeps or skiesBurnt the fire of thine eyes
On what wings dare he aspireWhat the hand dare seize the fire
Enceladus
shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)
shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice
shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute
Composite of UV (338 nm) green (568 nm) and IR (752 nm)
Why do we care
Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold
Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen
What is the origin of Enceladus internal heating Possibility of life
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeCould frame thy fearful symmetry
Cassini
Cassini entered orbit around Saturn on 1 July
2004 and it will orbit there for four years
Cassini has 12 instruments while the Hyugens probe
(which descended to Titans surface in January
2005) had 6
Cassini had three close flybys of Enceladus between Feb amp July
2005 One more scheduled for Spring
2008Credit NASA
Credit NASA
CIRS
Cassini Composite Infrared Spectrometer
Reference Flazar et al (2004)
In what distant deeps or skiesBurnt the fire of thine eyes
On what wings dare he aspireWhat the hand dare seize the fire
Enceladus
shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)
shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice
shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute
Composite of UV (338 nm) green (568 nm) and IR (752 nm)
Why do we care
Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold
Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen
What is the origin of Enceladus internal heating Possibility of life
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Cassini
Cassini entered orbit around Saturn on 1 July
2004 and it will orbit there for four years
Cassini has 12 instruments while the Hyugens probe
(which descended to Titans surface in January
2005) had 6
Cassini had three close flybys of Enceladus between Feb amp July
2005 One more scheduled for Spring
2008Credit NASA
Credit NASA
CIRS
Cassini Composite Infrared Spectrometer
Reference Flazar et al (2004)
In what distant deeps or skiesBurnt the fire of thine eyes
On what wings dare he aspireWhat the hand dare seize the fire
Enceladus
shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)
shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice
shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute
Composite of UV (338 nm) green (568 nm) and IR (752 nm)
Why do we care
Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold
Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen
What is the origin of Enceladus internal heating Possibility of life
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Cassini Composite Infrared Spectrometer
Reference Flazar et al (2004)
In what distant deeps or skiesBurnt the fire of thine eyes
On what wings dare he aspireWhat the hand dare seize the fire
Enceladus
shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)
shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice
shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute
Composite of UV (338 nm) green (568 nm) and IR (752 nm)
Why do we care
Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold
Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen
What is the origin of Enceladus internal heating Possibility of life
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
In what distant deeps or skiesBurnt the fire of thine eyes
On what wings dare he aspireWhat the hand dare seize the fire
Enceladus
shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)
shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice
shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute
Composite of UV (338 nm) green (568 nm) and IR (752 nm)
Why do we care
Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold
Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen
What is the origin of Enceladus internal heating Possibility of life
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Enceladus
shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)
shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice
shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute
Composite of UV (338 nm) green (568 nm) and IR (752 nm)
Why do we care
Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold
Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen
What is the origin of Enceladus internal heating Possibility of life
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Why do we care
Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold
Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen
What is the origin of Enceladus internal heating Possibility of life
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image
Credit NASAJPLGSFC
The Puzzle
Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash
inferred temperatures of 75 +shy 3 K
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat
What dread hand and what dread feet
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Figure 1(A) of Spencer et al (2006)
Cassini CIRS Observations of Enceladus
FarshyIR brightness temperature images of the thermal emission from the antishySaturn
hemisphere of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1
Thermal Model Fits to Determine Physical Properties
shy Temperatures near 76 K consistent with Voyager estimates
shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface
shy The high albedo is consistent with Voyager determination of 090 +shy 010
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
What the hammer what the chainIn what furnace was thy brain
What the anvil what dread graspDare its deadly terrors clasp
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Figure 2 of Spencer et al (2006)
Mid-IR Data on Enceladus South Pole
(125 to 16 microm)
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR
detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)
Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)
Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies
temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)
They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely
The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
What Causes the Hot Spot at the South Pole Is it seasonal effects
ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower
How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped
beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice
A heat source from withinndash Quite possibly The hot spot is located in a recently
resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Thermal Emission Associated with Individual Tiger Stripes
Figure 3 of Spencer et al (2006)
Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to
Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)
Properties of individual hot spots
Table 2 of Spencer et al (2006)
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
When the stars threw down their spearsAnd watered heaven with their tears
Did He smile His work to seeDid He who made the Lamb make thee
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the
dust and vapor plume seen by other Cassini instruments
Assuming
ndash the plume originates from thermal sublimation of warm water ice
ndash this warm ice is visible to CIRS Then using
ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~
5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~
Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Plume Hot SpotS amp Tiger Stripes
In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes
The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes
ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this
assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations
Tidal heating may generate 1shy10 GW
ndash Enceladus is in a 21 mean motion orbital resonance with Dione
ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Tiger Tiger burning brightIn the forests of the night
What immortal hand or eyeDare frame thy fearful symmetry
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Summary
Cassini CIRS found
ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K
Comparison with Cassini visual images
ndash most if not all of the heat is concentrated along the tiger stripe troughs
Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
References
ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401
ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169
ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393
wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)
Cassini home page at httpsaturnjplnasagovhomeindexcfm
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
The Tiger
Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet
What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry
shy William Blake (1757shy1827)
Image Credit NASA
Artists Conception of Enceladus
Image Credit NASA
Artists Conception of Enceladus