Titan: The Solar System’s AbioticPetroleum Factory
J. Hunter Waite, Ph.D.J. Hunter Waite, Ph.D.Institute ScientistInstitute Scientist
Space Science & Engineering DivisionSpace Science & Engineering DivisionSouthwest Research InstituteSouthwest Research Institute®®
Titan: The Solar System’s AbioticPetroleum Factory
Motivation for Titan Studies:
n Titan’s atmosphere is similar to Earth’s early atmosphere
n Titan may help us understand the origin of life in the solar system
n Titan may help us unlock the mysteries to organic formation in other regions of our galaxy and universe
Cassini Huygens Measurements
Orbiter In Situ Measurements
Mass Spectrometry
Mass Spectrometry
Cassini Huygens Measurements
Orbiter Remote Sensing Measurements
Infrared Spectrometry
Cassini Huygens Measurements
Probe Measurements
Cassini Huygens Measurements
Orbiter Radar Measurements
Methane Cycle
Possibilities for Titan Geology:What’s Cryo-Volcanism?
n Large rocky core; layers of liquid,water ice
n Abundant ammonia; melting pointof water ice lowered by ±100ºC
n Tectonism could breach crust; fluidcould reach surface
n Ammonia-water “cryo-lava” would erupt as gelatinous mass
A Model ofA Model ofTitanTitan’’s Interiors Interior
Cryo Volcanism
High Latitude Lakes
Methane Cycle
Interstellar Clouds
Organic Molecules in the Interstellar Medium, Comets and Meteorites: A Voyage from Dark Clouds to the Early Earth,Pascale Ehrenfreund & Steven B. Charnley, Annual Review of Astronomy & Astrophysics, 38:427-83, 2000
Stratospheric Composition
Dunes
Namid Desert Arabian Desert
Titan
Descent Sequence
Methane Cycle
Ion Neutral Mass Spectrometer
About the mission and the instrument
Geometry of the Ta, Tb and T5 trajectories: with respect to Titan
r
1on 4.
The Ion Neutral Mass Spectrometer The 2 INMS sources
In this presentation:
- Neutral densities from closed source
- Ion densities from open source
Note:
A molecule of N2 penetrating inside the closed source can be ionized and dissociatedinto N +
2 and N+ and beobserved in the detectomass channels 28 and
Atmospheric Structure Mass Spectrum recorded during Ta
N2 ‡
CH4 ‡
H2 ‡
The Ion Neutral Mass Spectrometer produces ion and neutral mass spectra
Neutral GasesIIoonnss
Titan Neutral Species Density Profiles
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
900 1000 1100 1200 1300 1400 1500 1600 1700
altitude (km)
dens
ity (c
m^-
3)
TA
T5T16
N2
CH4
H2
Titan Minor Neutral Species Density Profiles(All Flybys Co-added)
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
900 1000 1100 1200 1300 1400
altitude (km)
dens
ity (c
m^-
3)
C2H2C2H4C2H6C3H4C4H2ArC6H6
Relevance of INMS Observations
nEvolution of the atmosphere of Titan –Outgassing of the interior –Escape of gases from Titan
nProduction of organic compounds –Ion and neutral photochemsitry –The role of the magnetospheric interacation
Evolution of the Atmosphere:Outgassing of the Interior
n The isotopes of Argon tell usabout outgassing from the interior
– 40Ar tells us how much of the volatile material has been outgassed from the interior 4040ArAr
• 40Ar = 0.8 ppm --> ~2% ofinterior volatiles areoutgassed
– 36Ar tells us how volatile materials like molecular nitrogen and methane were formed
• 36Ar < 0.6 ppm --> mostnitrogen is derived fromammonia
3636ArAr
Evolution of the Atmosphere:Atmospheric Escape
n The isotopes of molecular nitrogen and methane tell us about escape of volatiles from the atmosphere
– The ratio of 14N to 15N in molecular 1414NN 1414NNnitrogen tells us how much of theatmosphere has escaped over 1515NN 1414NNgeological time
– The ratio of 12C to 13C in methanetells us about escape of methaneand isotopic fractionation from
1212C HC H44photodissociation of methane
1313C HC H44
Evolution of the Atmosphere: Atmospheric Escape
n The isotopes of molecular nitrogen tell us about escapof nitrogen
e
– The ratio of 14N to 15N in molecularnitrogen tells us how much of the atmosphere has escaped over geological time
– The change in the ratio as a function of altitude is due to diffusive separation in the presence of gravity
14N/15N Isotopic Ratios by Flyby
50
100
150
200
250
900 1000 1100 1200 1300 1400 1500 1600 1700altitude (km)
isot
opic
ratio
TA ingress TA egress T5 ingress T5 egress T16 ingress T16 egress
300
Evolution of the Atmosphere: Atmospheric Escape
n Methane isotopic ratios give us complimentary information 12C/13C Isotopic Ratios by Flyby
0
20
40
60
80
100
120
140
900 1000 1100 1200 1300 1400 1500 1600 1700altitude (km)
isot
opic
ratio
TA ingress TA egress T5 ingress T5 egress T16 ingress T16 egress
160
Evolution of the Atmosphere:Atmospheric Escape
n INMS also sees direct evidence of heating ofthe upper atmosphereof Titan by energeticparticles fromSaturn’s magnetosphere
Divergence betweenthe thermal exospheric
profiles and the INMS data(z>1600 km)
Evolution of the Atmosphere: Atmospheric Escape
nAnd these elevated coronal temperatures implyescape of nitrogen and methane
Evolution of the Atmosphere: Atmospheric Escape
n But not enough escape (10-4) to explain the implications of the measured isotopic ratio of molecular nitrogen
Isotopic Ratio INMS
value Terrestrial Reference
14N/15N 155 215 12C/13C 96 93.8
nnIIff wwee uussee tthhee tteerrrreessttrriiaall 1144NN//1155NN aass aa rreeffeerreennccee tthhiiss iimmpplliieess tthhaatt oovveerr 7700%%
ooff tthhee TTiittaann aattmmoosspphheerree hhaass eessccaappeedd oovveerr ggeeoollooggiiccaall ttiimmee,, ssiinnccee tthhee
lliigghhtteerr iissoottooppee ((1144NN)) eessccaappeess pprreeffeerreennttiiaallllyy wwiitthh rreeggaarrdd ttoo tthhee hheeaavviieerr
iissoottooppee,, 1155NN
nnHHoowweevveerr,, wwee nnoottee tthhaatt iinn ssppiittee ooff tthhee cchheemmiiccaall lloossss ooff mmeetthhaannee iinn tthhee
aattmmoosspphheerree aanndd iittss eessccaappee ffrroomm tthhee aattmmoosspphheerree tthhee vvaalluuee rreemmaaiinnss
cclloossee ttoo tthhee tteerrrreessttrriiaall vvaalluuee iimmppllyyiinngg rreessuuppppllyy wwiitthhiinn tthhee llaasstt
5500 mmiilllliioonn yyeeaarrss
JeanJean’’ss
escapeescape
ObservedObserved
escapeescape
AAttmmoosspphheerriicc EEssccaappee::
MMoolleeccuullaarr HHyyddrrooggeenn ffrroomm MMeetthhaannee CCoonnvveerrssiioonn EEssccaappeess
HH22 eeccaappeess
tthhrreeee ttiimmeess
ffaasstteerr tthhaann
eexxppeecctteedd
ffrroomm JJeeaann’’ss
eessccaappee
Ion Neutral Mass Spectrometer
Production of Complex Organics at High Altitude
via Ion Neutral Chemistry
Complex Carbon Nitrile Chemistry
n The neutral composition at 1200 kmin addition to the primaryconstituents N2, CH4, and H2 includes a host of hydrocarbons:C2H2, C2H2, C2H6,C3H4, C3H8, C4H2, HCN, HC3N, C2N2, and C6H6.
==> TITAN”S UPPER ATMOSPHERE IS A KEY SOURCE of CARBON NITRILE COMPOUNDS
n Correspondingly, the ionosphericcomposition has a complexhydrocarbon/nitrile chemistry thatincludes almost all possiblehydrocarbon and nitrile species through C7.
Average Mass1100 - 1300 km
0.001
0.01
0.1
1
10
100
1000
5 13 18 23 28 33 38 43 48 53 58 63 68 73 78 83 88 93 98Mass Number
Den
sity
(cm
-3)
N2 CH4 H2
C6H6
C3H4
C4H2
C7s
C6s C5s
C4s
C3s
HCNH+
CHCH55++
IV.2 The Composition: photo- and electron impact ionization and dissociations
n Nitrogen
n Methane
n Acetylene
n Ethylene
n Ethane
n H, H2, N, HCN, HC3N, C N2 2
IV.3 The Composition:the main ion-neutral scheme
n The chemical scheme starts from the photo- and electronimpact dissociation and ionization of Nitrogen and Methane
– Creation of the first key neutrals: C2H4 and HCN – Production of the major ions: H2CN+, C2H +
5 , CH + 3
IV.4 The Composition: the main ion-neutral scheme – production rates
fl Local time dependent
production rates
for C2H4
Local time dependentproduction rates ‡
for H2CN+
IV.5 The Composition: subsequent production of key hydrocarbons
n Production of hydrocarbons:
– C2H2 – CH3 – C2H6 – C4H2 – C3H8 ,…
Local time dependent ‡
production rates
for C2H6
INMS: Neutrals (~ 1200 km)
Species INMS (TA)
CH4 3.3 x 10-2
C2H2 2.8 x 10-4
C2H6 1.2 x 10-4
C3H4 4.0 x 10-6
C3H8 2.3 x 10-6
Waite et al. 2005
IV.6 The Composition: production of heavy hydrocarbons and key ions
Local time dependentproduction rates
for c-C6H6
‡
n Production of Hydro- Key
carbons: ions: – C H +
3 3 – CH5 – C3H4 – C2H +
3 – C6H6 – C3H +
5 – C6H +
7
IV.8 The Composition: neutral results – local time dependent density profiles (1)
N2 CH4
C2H2 C2H4
IV.10 The Composition: ion results – local time dependent density profiles (1)
Electron density
Density ofH2CN+
IV.11 The Composition: ion results – local time dependent density profiles (2)
C2H5 + C3H5
+
Ion Neutral Mass Spectrometer
An Increased Role for the Magnetospheric Interaction
and Nitrile Ion Chemistry
Solar Radiation
INMS: Ions (1100 - 1300 km)
IONOSPHERIC ALTITUDE PROFILES INMS T5 outbound
0.1
1
10
100
1000
10000
1000 1100 1200 1300 1400 1500 1600 1700Altitude (km)
Den
sity
(cm
-3)
172829415179TOT18Ne
TOTAL
HCNH+ C2H5+
C3H5+
C4H3+
C5H5N+, C6H7+
CH5+
ALT (km)SZA (deg) 135 138 140 141 142 143 143TIME from CA (s) 126 193 245 287 324 359 393
Electron Density
NH4+?
N2 N2+ CH3
+ C2H5+hv, e HCNH+
N2H+
H2
CH5+CH4 CH4
+
H2
hv, e
N+
hv, e
HCN+
C2H4+
C3H3+
C3H5+
C2H2+
C2H3+
C2H4+
C5H7+
hv, e
C5H9+
C5H5+
C3H2N+
C5H5N+
C2H4+
C4H5+ C6H5
+
C4H2
C4H3+
C2H2+
C2H3+
CnHm+
C7H7+
C11H9+
C4H2
C9H9+
C6H7+
C3H4
Black = CH4 Red = C2H2 Blue = C2H4Turquise = C2H6 Orange = C3H4Plum = N Green = proton transfer
Keller et al. model flowchart
n CxHy+H+
odd mass
n CxHyN+H+
even mass
INMS / Keller et al. model
Missing masses:
18, 30, 42, 54, 56
INMS / new Vuitton and Yelle model
New model flowchart
Ion Neutral Mass Spectrometer
Ultimate Fate of Complex Organics
Minor species determined from the mass spectral deconvolution with one sigma error.
Species INMS-Derived Values Stratospheric Values (1)
CH4 2.19 ±0.002 x 10-2 2.2 x 10-2
H2 4.05 ±0.03 x 10-3 1.1 x 10-3 C2H2 1.89 ±0.05 x 10-4 2.2 x 10-6 C2H4 2.59 ±0.70 x 10-4 – 5.26 ±0.08 x 10-4 9.0 x 10-8 C2H6 1.21 ±0.06 x 10-4 9.4 x 10-6 C3H4 3.86 ±0.22 x 10-6 4.4 x 10-9
C2H4 value depends on the value adopted for HCN.
Atmospheric Composition: Molar fractions estimated at 1174 km from the Ta data
(Closed source)
Stratospheric Composition
Cat Scratches
Acknowledgements
n National Aeronautics and Space Administration
n European Space Agency
n Jet Propulsion Laboratory
n Cassini-Huygens Science Teams
n Visual Infrared Mapping Spectrometer Team
n Radar Team
n Imaging Science Team
n Ion Neutral Mass Spectrometer Team
n Composite InfraredSpectrometer Team
n Gas Chromatograph MassSpectrometer Team
n SwRI Communications Department
Southwest Research Institute®
