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The composition of planetary atmospheres: a historical perspective

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Mariner 9 / IRIS (1973) R =2.4 cm-1, FTS. Temperature, water vapor and dust in ... Cometary impacts (e.g. Shoemaker-Levy 9) internal water. external water ... – PowerPoint PPT presentation

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Title: The composition of planetary atmospheres: a historical perspective


1
The composition of planetary atmospheres a
historical perspective
Emmanuel Lellouch
Observatoire de Paris, France
2
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

3
Overview
  • Early times (1905-1970)
  • The 1970s main concepts emerge
  • The 1980s and 1990s accumulating molecules
  • Recent spacecraft exploration (1995-2008)

4
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 A
CH4 8900 A
5
First detections…
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 
Detection of methane in Titan
6
First detections…
Spinrad et al. 1963
  • Detection of H2 in Uranus

Identification of CH4 and NH3 in  visible spectra
of Jupiter and Saturn taken by Slipher in 1905
7
First detections…
1932
8
Beyond photography the beginning of infrared
(courtesy Dale Cruikshank)
During the war, Kuiper learned about the
development of IR detectors (PbS) having
sensitivity up to 3 ?m
Kuiper 1947
CH4 in Jupiter
? CO2 in Venus
9
The beginning of infrared…
CO2 on Mars (Moroz, 1964)
Vassili Ivanovich Moroz
10
Too much enthusiasm…
Sinton et al. 1960
1960
Actually due to telluric HDO
11
Mars discovery of atmospheric water in 1963
Water cycle on Mars
12
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
13
The solar reflected component of Venus
  • Detection of HCl, HF and CO in Venus (above
    clouds)
  • Michelson inteferometer R 20000
  • Connes et al. 1967, 1969
  • But
  • H2O difficult to detect
  • O2, O3 not detected
  • How to probe below the clouds ?

14
The 1970s The thermal infrared access to
physical concepts
15
C2H6
In the thermal range
  • Sensitive to temperature
  • Sensitive to vertical distribution of gases

16
Exploring the thermal range from Earth the 10 µm
window
Detection of strong hydrocarbon emission in outer
planets
C2H6
C2H6
Saturn Titan
Gillett et al. 1973, 1975 (R 60)
17
Methane photochemistry in Giant Planets (a recent
view…)
Moses et al. 2000 (Saturn)
18
Methane photochemistry in Giant Planets (a recent
view…)
Detection of C3H4 and C4H2 on Neptune IRS/Spitzer
, R600 Meadows et al. 2008
19
Stratospheres
Warmer on Titan (170 K) than Saturn (140
K) Predicted due to haze (esp. Titan) and
methane heating
Pre-Voyager models of Titan - inversion only ? -
greenhouse also?
Hunten, 1973
20
Equilibrium vs disequilibrium species in Giant
Planets
At the relevant T, NH3 is the thermodynamical
equilibrium form of N ? In principle NH3 / H2
gives the N/H ratio … but PH3 is NOT the
equilibrium form of P Competition between
chemical destruction and vertical convective
transport Quench level where tchem
tdyn Occurs at T 1200 K for phosphine ?
Observed PH3 abundance still gives P/H ratio !
21
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 ltlt CH4)

22
Vertical profile of NH3 in Jupiter physical
processes and deep 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 probed
  • NEED FOR DEEP IN SITU PROBE

23
The 1970s First global views of the planet
infrared spectra
24
Telluric planets from space a full view of the
thermal IR spectrum
MARS Mariner 9 / IRIS (1973) R 2.4 cm-1,
FTS Temperature, water vapor and dust in the
martian atmosphere VENUS Venera 15/ Fourier
Spectrometer (1983), R 2 cm-1 Temperature and
composition field at and above Venus clouds (H2O,
SO2, H2SO4)
25
Full spectra of Giant Planets Helium
He/H in Giant Planets
H2-He
Saturn IRIS / Voyager R 4.3 cm-1 He (Jup) He
(Sat) lt He (U) He (N) He (protosolar) ?
Evidence for helium segregation in Jupiters and
Saturns interior Thermal balace of Giant
Planets (internal source)
26
Full spectra of Titan chemistry
IRIS / Voyager R 4.3 cm-1
Voyager /UVS
N2 is dominant species in Titan
? Coupled photochemistry of N2 and CH4
27
1980-2000 Accumulating molecules (the golden
age of infrared)
28
From the ground the power of spectral resolution
Fourier Transform Spectrometer at
CFHT (1983-2000) 0.9 5.2 µm, InSb, InGaAs
detectors Best spectral resolution 0.01 cm-1
29
Exploiting the 5-µm region
More disequilibrium species in Jupiter and
Saturn CO, GeH4, AsH3
Detection of arsine (AsH3 ) in Saturn FTS/CFHT,
R22000 Bézard et al. 1990 ?
As / H 5 times solar
Jupiter and Saturn are enriched in heavy elements
(C, N, P, As) Saturn more than Jupiter
30
Deuterium in the Solar System
. Venus
Venus
Detection of CH3D in Neptune CFHT/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 and atmospheric
escape
31
A new, key, species
H3 on Jupiter
FTS/CFHT, R 15000 Maillard
et al. 1990
See J.P. Maillards and S. Millers talks
32
Probing below Venus clouds
H3 on Jupiter
FTS/CFHT, R 25000 Bézard et al. 1989
The uppermost clouds form a curtain and by day
reflect sunlight back to dazzle us. By night,
however, we become voyeurs able to peep into
the backlit room behind D. Allen, Icarus, 1987
33
(No Transcript)
34
ISO External water in outer planets
? external water
?internal water
ISO/SWS R1500 Feuchtgruber et al. 1997
  • Interplanetary dust ?
  • Planetary environments (satellites, rings?)
  • Cometary impacts (e.g. Shoemaker-Levy 9)

35
Comets are sources for atmospheres
HST Noll et al. 1995
1995
16-23 July 1994

JCMT 15-m Moreno et al. 2003
36
Recent exploration from spacecrafts (1995-2008)
37
Spectroscopy from recent space missions the 3-D
view
Titan Cassini CIRS/(R0.5 cm-1)
Study of couplings between chemistry and
dynamics … but no new detections (except many
isotopes)…

38
In situ measurements the chemical complexity of
Titans upper atmosphere from Cassini / INMS
39
In situ measurements methane profile and
meteorology in Titans atmosphere from Huygens
Methane drizzle on Titan (Tokano et al. 2006)
40
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…
41

Why even bother
to go there?
42
Detection of J2O on Earth (Cambridge 2005 DPS
meeting)
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