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: OBSERVATIONS WITH ODIN

Biver et al., 2004

Ozone on Mars with Herschel

NH3 on Mars with Herschel and ALMA(Q= 5 10-10)

Herschel

ALMA

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

HD: ISO/SWSFeuchtgruber et al., 1999

Lellouch et al., 2001

Deuterium in theSolar System

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

He/H in the giant planets

Jupiter: Galileo mass spectrometerSaturn, Uranus, Neptune: Voyager (IRIS)

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

Bergin et al. 2000

Observation of the H2O vertical distribution in Jupiter with SWAS

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)

Detectability of stratospheric CH4 in Uranus and Neptune with Herschel/PACS

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

Sensitivity (1 - 1h) = 0.6 mJy

HERSCHEL/SPIRE 250 micron

Detectability of TNOs with Herschel/SPIRE

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 ISO: high-resolution spectroscopy of rovibrational bands

Crovisier et al., 1997

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