Solar-system observations with Herschel/ALMA
T. Encrenaz, D. Bockelée-Morvan,
J. Crovisier, E. LellouchLESIA, Observatoire de Paris
Outline
• Why the far-IR/submm/mm range?
• Major objectives of solar-system research
• Venus, Mars and the giant planets
• Satellites, distant asteroids and TNOs
• Comets
Why the far-IR/submm/mm range?
• Solar-system objects are COLD objects which radiate at low frequencies
• Strong molecular rotational transitions
• Ideal for:– planetary atmospheres– cometary atmospheres – distant objects (TNOs)
Many major discoveries in planetary and cometary science
• First detection of HCN in Comet Halley (1986)
• Over 20 parent molecules detected in Hale-Bopp (1997)
• First detection of a stable atmosphere (SO2) around Io (1990); also SO and NaCl(2002)
• Detection of new molecules in Jupiter after the SL9 collision (1994):CO, CS, OCS, HCN
• First detection of H2O2 on Mars (2004)
Major issues in solar-system sciences
• Origin of the solar system: – Giant planets ’ composition: D/H, He/H, oxygen source– Comets ’ composition and link with ISM: minor
constituents, D/H in various species– TNOs: Ts/albedo
• Evolution of solar-system objects– Minor constituents and dynamics of planetary and
satellite atmospheres– Comets ’ activity, physico-chemistry and
thermodynamics
Venus
• CO, H2O/HDO observed in the mm range -> vertical distributions + wind measurements
• No observation with ISO nor Herschel• Perspective with ALMA:
– velocity field from CO, H2O, H218O maps (-> D/H)
• dynamics of the mesosphere (z = 100 km):zonal super-rotation, global circulation
– Search for minor mesospheric species (HCl, H2S, SO2)
• Follow-up of Venus Express
Mars: a prime objective of planetary exploration
• Questions:– Past and present climate– Water cycle– Evidence for liquid water in the past?– Evidence for traces of fossil life?
• An extensive space exploration with orbiters and landers (« Follow the water »)
Mars:High-resolution spectroscopy
• CO, H2O/HDO/H218O observed in the mm range -
> vertical distributions • ISO, Odin, SWAS -> water distribution• Perspectives with Herschel and ALMA:
– H2O, CO and isotopes (in part. D/H)– Minor species: H2O2, O2, O3
– Search for undetected species: HCl, NH3, HO2, H2CO, SO2, H2S, OCS…
Mars: A 3-D dynamical picture of the middle atmosphere
(winds, T(P) and water mapping)• First maps using CO(2-1) at IRAM (30m & PdB)• Comparison with GCM: good overall agreement
but strong retrograde winds observed whatever the season
• -> future observations important for better understanding the martian climate
• -> Major objective for ALMA• Complementarity with space missions
(Mars Express and future orbiters )
Mars velocity field, IRAM PdB (Moreno, 2001) z = 50 -70 km
Perspectives with ALMA: V = 3-5 m/s, spatial resolution on Mars: about 100 km
Giant planets: formation
• D/H: a tracer of giant planets ’ formation– In Jupiter and Saturn (mostly made of
protosolar gas): reflects the protosolar value– In Uranus and Neptune ( mostly made of an icy
core): enriched vs protosolar value– Expected:
• (D/H)PS=(D/H)J <(D/H)S<(D/H)U,N<(D/H)C
• Confirmed by ISO & Galileo measurements
What to do with Herschel?
• New measurement of HD at 56 and 112 m on the four giant planets with PACS
• Questions:– Is (D/H)S > (D/H)J ?
– Are (D/H) in protoneptunian ices different from cometary values?
– Is D/H in Oort-cloud comets the same as in Kuiper-Belt comets?
Giant planets: evolution• He/H: a tracer of giant planets ’ evolution
– In Jupiter and (even more) in Saturn: He is expected to be depleted vs the protosolar value due to condensation in liquid hydrogen during the cooling phase
– In Uranus and Neptune:
• no liquid hydrogen expected
• but H partly linked in ices
• -> He/H might be enriched in the gas phase
– Present determination are still uncertain (except Jupiter)
– Future: Cassini CIRS (Saturn), Herschel/PACS (Uranus,Neptune), from the far-IR continuum
The oxygen source in the giant planets and Titan
• H2O and CO2 emissions detected by ISO-SWS + SWAS/ODIN (Jupiter, Saturn)
• Comparable H2O input fluxes: 105-107 cm-2 s-1
• Possible sources:
– interplanetary flux (U, N),
– local source (rings, satellites)(S, T?),
– cometary impacts (J?)
• Important implications on:
– Dust production and water content at large Rh (collisions in the Kuiper Belt?)
– Rate of cometary impacts
Oxygen source: What to do with Herschel and ALMA?
NB: For Saturn: complementarity Herschel/Cassini-CIRS
• Herschel: – H2O abundance and variability
• Possible role of cometary impacts– H2O vertical distribution (HIFI)
• Constrains on transport models– Low-resolution mapping of J and S (PACS)
• Possible trapping in aurorae
• ALMA: HDO high-resolution mapping• Determination of D/H in external source?
Why are Uranus and Neptune so different?
• Strong internal source in Neptune, not in Uranus
• CO and HCN abundant in Neptune ’s stratosphere (CON = 10-6, COU = 3 10-8)
• CO mostly internal in Neptune, probably external in Uranus
• Uranus is much more sluggish (eddy diffusion coefficient 103 times less than in Neptune)
What to do with Herschel and ALMA?
• Search for tropospheric CO and PH3 (tracer of vertical motions in Jupiter and Saturn ’s tropospheres)– PH3 expected to be abundant in Neptune, apparently
absent in Uranus (convection inhibited?)
• Search for CH4 emission lines – oversaturation observed in Neptune, not in Uranus
• Search for photochemical products in Neptune (nitriles)
Satellites & Pluto with ALMA• Io
– Search for minor species (H2S, S2O, KCl, SiO…) – SO2 low-res. Mapping (-> volcanism monitoring)
• Titan (complementarity with Cassini/CIRS)– Mapping of CH3CN, HC3N at z = 500 km
-> dynamics, photochemistry– HCN: winds (low-res.map), D/H
• Triton and Pluto– Search for CO, HCN…
Distant asteroids and TNOs
• Interest of far-IR/submm measurements: determination of diameter + Ts (in the visible: aD2 is measured)
• Spitzer program (GTO): 114 TNOs, 14 Centaurs
• With Herschel: possible to reach D=300 km at 40 AU
• With ALMA: 300 km at 80 UA
Observations of comets with Herschel and ALMA (1)
• Water-rich objects ->Study with Herschel– Activity monitoring– D/H -> origin
– Tinitial from ortho/para ratio -> origin
– Tcoma from H2O line intensities -> thermodynamics
– Doppler shifts -> velocity fields -> thermodynamics, study of jets...
• Many complex parent molecules -> study with ALMA– Search for new species (possible candidates: all ISM
molecules!)– Chemical diversity among comets– Relative abundances -> link with ISM– Isotopic ratios (D/H in HCN, HNC, H2CO…) -> link
with ISM– Velocity fields -> thermodynamics, origin of
outgassing (nucleus, grains), structure (jets)
Observations of comets with Herschel and ALMA (2)
The heritage from SWAS: the 557 GHz line in comet C 1999 H I (Lee)
About 12 comets observed with SWAS and/or ODIN
The heritage from ground-based observations:Evolution of production rates with heliocentric distances
Biver et al.,2002
Parent molecules observed in comets• In the far-IR/radio range:
– H2O, CO, CH3OH, H2CO, HCN, H2S
– NH3, HNCO,CH3CN,HNC, OCS (Hyakutake)
– HCOOH, CH3CHO, HCOOCH3, NH2CHO, HC3N, H2CS, SO, SO2 (Hale-Bopp)
• In the near-IR range:– H2O, CO, CO2, H2CO, OCS, saturated & unsaturated
hydrocarbons
– CH4, C2H2, C2H6, OCS, NH3 (Hyakutake, Hale-Bopp)
Water in comets (Herschel)
• H2O in a sample of weak comets (down to Q=1026 s-1)-> prod. rates (HIFI, 557 GHz)
• H2O monitoring as a function of Rh (HIFI, 557 GHz)
• Search for H2O in distant weakly active objects (link with asteroids)
• Measurement of D/H in H2O
D/H in comets
• D/H in water: a stringent clue to the formation of comets (T, Rh)
• D/H is known for only 3 Oort-cloud comets, not for Kuiper-belt comets
• HDO lines will be searched for with HIFI for bright comets (Q > 2 1028 s-1)
• D/H in other species (HCN, HNC…) will be searched for with ALMA
• 8P/Tuttle January 2008, Q[H2O] = 3. 1028 s-1 = 0.25 AU
• 46P/Wirtanen February 2008, Q[H2O] = 1. 1028 s-1
• 85P/Boethin December 2008, Q[H2O] = 3. 1028 s-1 • 67P/Churyu.-G December 2008, Q[H2O] = 5. 1027 s-1
• 22P/Kopff May 2009, Q[H2O] = 2.5 1028 s-1
• 81P/Wild 2 February 2010, Q[H2O] = 1.3 1028 s-1
• 103P/Hartley 2 October 2010, Q[H2O] = 1.2 1028 s-1 = 0.12 AU
A few good targets for Herschel
+ possible brighter targets as Targets of Opportunity
ALMAInstantaneous 3-D maps of gaseous and dust (thermal) emissionsComa morphology, spiral gaseous jets, nucleus outgassing, rotation properties, dust/gas linksGas temperature and velocity mapsNucleus thermal emission on long baselines: size, albedo
CO 230 GHz/Hale-Bopp with IRAM PdB
Mapping cometary atmospheres
Henry,2003
In summary...• Herschel/ALMA observations of solar-system objects
will be precious in addition to space missions (MEx, VEx, Rosetta)
• D/H in the solar system-> origins• Search for minor species in comets-> link with the ISM• Observation of many samples (KB comets, TNOs)• High-resolution mapping of planets and satellites
• A major program with Herschel: H2O in the solar system • Formation of planets and comets• Activity of outer small bodies and water content in outer
planetesimals