The study of planetary atmospheres with ALMA

Transcription

1 The study of planetary atmospheres with ALMA Emmanuel Lellouch Observatoire de Paris, France

2 Planetary atmospheres in mm/submm Spectrally resolved measurements of molecular lines Thermal sounding, i.e. determination of p-t-z profiles Chemical sounding, i.e. molecular abundances and their vertical profiles Dynamical sounding, i.e. wind velocities from Doppler shift measurements These three parameters are intimately coupled Temperature field wind field Wind field horizontal/vertical distribution of minor species Minor species temperature field through atmospheric heat budget (heating, cooling)

3 Why ALMA Spatial resolution and uv coverage Largest baseline 15 km resolution = at 1 mm In practice, S/N limitations typical spatial resolutions ~ , i.e. ~100 km à 1 UA, 1000 km à 10 UA uv plane coverage «instantaneous» imaging Sensitivity Acces to weaker lines, notably on tenuous and/or distant objects (e.g. Pluto) Spatial resolution possibility of limb sounding, improving detection sensitivity (but no vertical resolution at limb)

4 Why ALMA The broad IF bandwidth: 2x8 GHz Favorable for the search of broad lines in «deep» atmospheres (Venus, Giant Planets) Favorable for detection sensitivity in continuum mode A southern telescope General goal of ALMA observations: study of couplings between composition and atmospheric dynamics from 3-D measurements of abundances, temperature fields and winds

5 Planetary atmospheres: some objectives for ALMA Dynamics of Mars and Venus atmospheres Martian water cycle Minor species in Mars and Venus atmospheres Titan s photochemistry-dynamics couplings Oxygen in outer planets Evolution of Jupiter s atmosphere after SL9 Giant Planet tropospheres : composition and temperatures Tenuous atmospheres: Io, Enceladus, Pluto, Triton, KBOs

6 The dynamics of Mars and Venus middle atmospheres Thermal and wind sounding from CO lines Temperature profile: Mars at 0-80 km, Venus at km Wind measurements from Doppler shifts, near km on Mars and km on Vénus Not unique (thermal sounding from CO2 from spacecrafts) Unique even in space era Current results: Mars Wind are strong (~100 m/s) and retrograde at all seasons except during dust storms: OK with models at solstice but not at equinox East/West asymetries. Geographical variations?

7 Winds on Mars (PdB, CO(1-0)) R. Moreno et al.

8 Solstice Near Equinox Retrograde ~ 100 m/s Retrograde+jets+ asymetries Equinox + dust storm Direct + jets + asymetries

9 The dynamics of Mars and Venus middle atmospheres Current results: Venus Coexistence of 2 wind regimes at km (mesosphere) Retrograde super-rotation Subsolar antisolar flow Strong temporal variability on all timescales (from days to years) Strong coupling with the horizontal distribution of CO and other tracers ALMA: spatial and temporal resolution Study of jets, waves and other local structures (e.g. orographic for Mars) Good uv coverage «instantaneous» imaging short timescale variability

10 VENUS: rapid (1 week) variability of wind field and CO distribution above clouds Clancy et al. 2006

11 The martian water cycle The vertically-integrated column of H2O is strongly variable with season and latitude reflecting exchanges with polar caps The vertical profile of H2O is poorly characterized, but also seems to vary with season (from mm obs.)

12 Vertical distribution of H2O on Mars «The variable hygropause»; implications for water transport and chemistry Clancy et al Aphelion Perihelion

13 The martian «deuterium cycle» A subtle fractionation effect during the water condensation HDO vapor pressure slightly < H2O vapor pressure At cloud formation, condensed-phase is enriched in D and gas-phase is depleted in D D/H ratio expected to show vertical and latitudinal variations!! Important to understand to interpret D/H ALMA: seasonal maps of H2O (from 183 GHz or from H218O) and HDO. Montmessin et al. 2005

14 Chemistry in Mars and Venus atmospheres Search for new species / monitoring of known species to improve understanding of photochemistry Mars: CO2 + H2O CO, O2, O3, H2O2 ALMA: Study correlations /anticorrelations between H2O, O3, H2O2 and search for new species Venus: additional presence of Cl- (HCl) and S- (SO2, H2SO4, OCS) species below clouds. Catalytic role of chlorine in chemical cycles ALMA: Study composition of atmospheres above clouds. Search for SO2, H2S, OCS, NO, O2, HCl

15 A few recent ( ) results from JCMT (Clancy and Sandor) HDO 226 GHz SO2 346 GHz Huge variability of H2O above Venus clouds First mm detection of SO2 on Venus First detection of H2O2 on Mars

16 Titan: a strongly coupled system Circulation Winds Waves chemistry Detailed composition (hydrocarbons, nitriles) polymerization condensation Hazes nucleation Clouds scavenging Radiative properties Thermal field transport trans port transport (horizontal and vertical) energy sources on sati den con Main composition (N2, CH4) Escape

17 Titan chemistry-dynamics couplings 10 C2H C2H HCN C3H8 10 C2H HC3N 10 CO C2N2 C3H4 Rannou et al et 0al Hourdin 10-9 C4H2 Latitude Latitude Flasar et al 2005

18 Titan at (sub)mm wavelengths SMA, Gurwell 2005 IRAM PdB Moreno et al IRAM 30-m Marten et al cf also R. Moreno s poster Winds in HC3N km Winds in CH3CN km

19 Titan (0.8 ) with ALMA (R~0.1 ) Fine structure of winds (mid-latitude jets, expected from models) 3-D mapping of detectable species: CO, HCN, HC3N, CH3CN and their C,N isotopes NB. Cassini will stop in Search for new species CH3CCH, C2H3 CN, C2H5CN, NH3 (detected by Cassini during upper atmosphere flybys) Isotopic ratios: D/H in HCN and H2O: fractionation effects w.r.t. D/H in CH4

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21 Titan (0.8 ) with ALMA (R~0.1 ) Titan meteorology: maps of tropospheric temperature (i.e. T near 30 km) from mm continuum unique constraint to meteorological models (CH4 cloud formation processes ) Temporal monitoring (30 years) of all the above! Kim and Courtin 2002

22 Giant planets Different kind of lines Narrow (< 50 GHz), stratospheric emissions. Ex. H2O,HCN Broad (> 2 GHz) tropospheric, absorptions. Ex. PH3 Absorption+emission. Ex. CO on Neptune ALMA multi-resolution mode well suited. NEPTUNE IRAM 30m JUPITER H2O 557 GHz SWAS SATURN PH3 267 GHz CSO + FTS CO 230 GHz

23 Giant Planets : some goals for ALMA (1) The nature of the oxygen source Giant Planets and Titan contain oxygen compounds (H2O, CO2, CO) Origin? Internal (primordial oxygen) External (cometary impacts, micro-meteoritic flux, rings?) Both sources are present for H2O. CO ambiguous ALMA Determine vertical profiles Saturn, Uranus. Is CO present in stratosphere? Search for latitudinal variations of CO and H2O (ring signature?) Search for HDO in stratosphere D/H external water,a clue to origin? Strongly related to Herschel KP

24 Giant Planets : some goals for ALMA (2) Evolution of the species (CO, CS, HCN) deposited by the Shoemaker-Levy 9 impact with Jupiter in 1994 Impact latitude HCN distribution in 2000 from Cassini Moreno et al Lellouch et al. 2006

25 Giant Planets : some goals for ALMA (3) Tropospheric composition / temperature structure Line Maps of phosphine (PH3) in Jupiter and Saturn Search for PH3 in Uranus et Neptune P/H, unknown so far. Search for new compounds (HCP, halides, H2S, etc ) Continuum studies : maps of temperature and humidity of volatile species (NH3) Uranus: VLA 6 cm - Hofstadter et al See Mark Hofstadter s talk Saturn from OVRO-BIMA 2005 Dunn et al.

26 Tenuous atmospheres: Io (1 ), Enceladus (0.15 ) Io s atmosphere P ~ nbar, spatially heterogeneous SO2 ~ 90 %, SO, NaCl, S2) ALMA: mapping at R ~0.2 Localisation of sources Atmospheric dynamics from lineshifts: planetary-scale winds, volcanic plumes Search for new compounds (S2O, KCl, H2S, ClO, SiO ) : chemistry Clues on atmospheric origin (sublimation vs. volcanic venting) Enceladus atmosphere Io winds (km/s) with PdB: see A. Moullet s poster H2O, ~1016 cm-2 above South Pole, traces of CO, N2 ALMA: map CO, H2O

27 Tenuous atmospheres: Pluto, Triton, KBOs Pluto : p ~5 µbar, currently increasing Triton: p ~ 15 µbar Pluto: non-detection of CO N2 + ~1 % of CH4 In surface equilibrium ALMA: search for CO (and HCN) Chemistry Thermal structure IRAM 30m Bockelée-Morvan et al Extend studies to other «dwarf planets» (Eris) and large trans-neptunian objects (2003 EL61, 2005 FY9)

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