Date post: | 01-Jan-2016 |
Category: |
Documents |
Upload: | blondelle-kayson |
View: | 41 times |
Download: | 1 times |
The composition of planetary atmospheres:
a historical perspective
Observatoire de Paris, France
Emmanuel Lellouch
Atmospheres of the Solar System
• Giant Planets– Primary atmospheres (H2, He, CH4…)
– Little evolution (no surface, little escape)
• « Terrestrial » planets (Earth, Venus, Mars, Titan)– Secondary atmospheres (CO2 / N2, N2 / O2, N2 / CH4)
– Outgassed and strongly evolved (escape, surface interaction)
• Tenuous atmospheres (Pluto, Triton, Io, Enceladus)– In equilibrium with surface ices or internal sources
• Exospheres (Mercury, Moon, other Galilean satellites)– Solar flux or solar wind action on surfaces
Overview
• Early times (1905-1970)• The 1970’s: main concepts emerge• The 1980’s and 1990’s: accumulating molecules• Recent spacecraft exploration (1995-2008)
First detections: the visible range
Wildt 1932
Identification of CH4 and NH3 in visible spectra of Jupiter and Saturn taken by Slipher in 1905
CH4 7260 ACH4 8900 A
First detections…
Detection of methane in Titan
Kuiper 1944
« The only reason why I happened to observe the planets and the 10 brightest satellites was that they were nicely lined up in a region of the sky where I had run out of programs stars »
First detections…
Detection of H2 in Uranus Spinrad et al. 1963
Identification of CH4 and NH3 in visible spectra of Jupiter and Saturn taken by Slipher in 1905
First detections…
1932
Beyond photography: the beginning of infrared (courtesy Dale Cruikshank)
During the war, Kuiper learned about the development of IRdetectors (PbS) having sensitivityup to 3 m
CO2 in Venus
CH4 in Jupiter
Kuiper 1947
The beginning of infrared…
CO2 on Mars (Moroz, 1964)Vassili Ivanovich Moroz
Too much enthusiasm…
Sinton et al. 1960
1960
Actually due to telluric HDO
Mars: discovery of atmospheric water in 1963
Detection of H2Oon Mars (Spinrad et al. 1963) at 0.82 micron:
“Watershed” discovery
R ~100000
Mars
Water cycle on Mars
Mars’ atmosphere: basic chemistry
* Detection of CO (1968) * Detection of O2 1.27 emission in 1976 O3 (1971), and O2 (1972) tracer of ozone (and not vice versa!)
*CO2 + h CO + O *O + O + M O2
*O2 + O + M O3
*H2O + h OH +H*CO + OH CO2 + H (stability of atmosphere)*OH HO2 H2O2
(not detected before 2005)
Noxon et al. 1976
The solar reflected component of Venus
Detection of HCl, HF and CO in Venus (above clouds) Michelson inteferometer R ~ 20000Connes et al. 1967, 1969
But: - H2O difficult to detect- O2, O3 not detected- How to probe below the clouds ?
The 1970’s: The thermal infrared:access to physical concepts
C2H6
deTBI
))((0
In the thermal range:
• Sensitive to temperature• Sensitive to vertical distribution of gases
Exploring the thermal range from Earth: the 10 µm window
Detection of strong hydrocarbon emission in outer planets
Gillett et al. 1973, 1975 (R ~60)
C2H6 C2H6
Saturn Titan
C2H6
Moses et al. 2000(Saturn)
Methane photochemistry in Giant Planets(a recent view…)
Detection of C3H4 and C4H2 on NeptuneIRS/Spitzer, R=600Meadows et al. 2008
Methane photochemistry in Giant Planets(a recent view…)
Stratospheres
Hunten, 1973
Pre-Voyagermodels of Titan:- inversion only ?- greenhouse also?
Warmer on Titan (~170 K)than Saturn (~140 K)
Predicted due to haze (esp. Titan) and methaneheating
Equilibrium vs disequilibrium species in Giant Planets
At the relevant T, NH3 is thethermodynamical equilibrium form of N In principle NH3
/ H2 gives the N/H ratio
… but PH3 is NOT the equilibriumform of P
Competition between chemical destruction and vertical convective transportQuench level : where tchem ~ tdyn
Occurs at T ~1200 K for phosphine
Observed PH3 abundance still gives P/H ratio !
Exploring the thermal range from Earth: the 5-µm window of the Giant Planets
Hot radiation originating from ~ 3-5 bar levels (due to low H2 and CH4 opacity)
- NH3, PH3
- New detections in 1973-1975: H2O (equilibrium) CO (disequilibrium, much << CH4)
Vertical profile of NH3 in Jupiter: physical processes and deep abundance
10 µm + UV 5 µm
Photolysis
Condensation
“Bulk abundance” ?
NH3 / H2 at ~3 bar indicates N/H on Jupiter is enriched by a factor ~2 over solar
H2O : Does not give O/H ratio because H2O condensation occurs deeper than levels probedNEED FOR DEEP IN SITU PROBE
The 1970’s: First global views of the planet infrared spectra
Telluric planets from space: a full view of the thermal
IR spectrum MARSMariner 9 / IRIS (1973)R =2.4 cm-1, FTS
Temperature, water vapor and dust inthe martian atmosphere
VENUSVenera 15/ Fourier Spectrometer(1983), R = 2 cm-1Temperature and composition fieldat and above Venus clouds (H2O, SO2, H2SO4)
Full spectra of Giant Planets: Helium
Saturn IRIS / Voyager R = 4.3 cm-1He (Jup) ~ He (Sat) < He (U) ~ He (N) ~ He (protosolar) Evidence for helium segregation in Jupiter’s and Saturn’s interior
+ Thermal balace of Giant Planets (internal source)
H2-He
He/H in Giant Planets
Full spectra of Titan: chemistry
IRIS / Voyager R = 4.3 cm-1
* N2 is dominant species in Titan
* Coupled photochemistry of N2 and CH4
Voyager /UVS
1980-2000: Accumulating molecules
(the golden age of infrared)
From the ground: the power of spectral resolution
Fourier Transform Spectrometer at CFHT(1983-2000)0.9 – 5.2 µm, InSb, InGaAs detectorsBest spectral resolution ~ 0.01 cm-1
Jean-Pierre Maillard
Exploiting the 5-µm region
More disequilibriumspecies in Jupiterand Saturn
CO, GeH4, AsH3
Detection of arsine (AsH3 ) in SaturnFTS/CFHT, R=22000 Bézard et al. 1990 As / H ~ 5 times solar
Jupiter and Saturn are enriched in heavyelements (C, N, P, As); Saturn more than Jupiter
Deuterium in the Solar System
Detection of CH3D in NeptuneCFHT/FTS, R = 1600 (de Bergh et al. 1990)
* Owen et al. Nature, 1986. Deuterium in the outer solar system – Evidence for two distinct reservoirs
* D/H enriched in Mars and Venus H2O: Evidence for H2O photolysis andatmospheric escape
. VenusVenus
A new, key, species
H3+ on Jupiter
FTS/CFHT, R= 15000 Maillard et al. 1990
See J.P. Maillard’sand S. Miller’s talks
Probing below Venus’ clouds
H3+ on Jupiter
FTS/CFHT, R= 25000Bézard et al. 1989
The uppermost clouds form a curtainand by day reflect sunlight back todazzle us. By night, however, we become voyeurs able to peep into the backlit room behind
D. Allen, Icarus, 1987
ISO: External water in outer planets
ISO/SWSR=1500Feuchtgruber et al. 1997
Jupiter
Saturn
NH4SHH2O
NH3
• Interplanetary dust ?• Planetary environments (satellites, rings?)• Cometary impacts (e.g. Shoemaker-Levy 9)
internal water
external water
Comets are sources for atmospheres
JCMT 15-mMoreno et al. 2003
HST Noll et al. 1995
199516-23 July 1994
Recent exploration fromspacecrafts (1995-2008)
Spectroscopy from recent space missions: the 3-D view
Study of couplings between chemistry and dynamics
… but no new detections (except many isotopes)…
TitanCassini CIRS/(R=0.5 cm-1)
In situ measurements: the chemical complexity of Titan’s upper atmosphere
from Cassini / INMS
In situ measurements: methane profile and
meteorology in Titan’s atmosphere from Huygens
Methane drizzleon Titan(Tokano et al. 2006)
In situ measurements: elemental abundances and meteorology in Jupiter from Galileo
C/H, N/H, S/H are all 3 times solar
Noble gases are also 3 times solar.
O/H is still not measured…
Why even bother
to go there?
Detection of J2O on Earth (Cambridge 2005 DPS meeting)