Solar System observations with APEX Observatoire de Paris, France Emmanuel Lellouch

A few commonplaces Improved sky transmission with respect to currently available facilities (JCMT, CSO, IRAM, etc…) –Lower noise level in bands covered by other telescopes (1300,800,450,350 µm) –Higher frequencies available (1.0 THz, 1.3 THz)  access to stronger lines and/or new molecules –However, T sys worse at higher freqs  compromises and feasibility to be studied ‘’Small’’ antenna (compared to IRAM-30 m)  dilution effects more severe (esp. for planets) –Partly compensated by higher working frequencies e.g. beam = 7’’ at 820 GHz = 30-m telescope beam at 330 GHz A Southern hemisphere telescope Solar System objects are moving  need to implement a tracking system – position, velocity – for planets, comets, satellites

Areas Planetary atmospheres Cometary atmospheres Small bodies (continuum) ??

Planetary atmospheres at mm/submm wavelengths Molecular lines  –Molecular abundances and vertical profiles –Thermal sounding –Wind sounding (Doppler shift) –Bandwidth ~ 1 GHz  sounded pressures < 0.3 bar Thermal / wind sounding requires spatial resolution Venus Mars Jupiter Io Saturn Titan Uranus Neptune Pluto 10-60’’ 5-25’’ 45’’ 1’’ 18’’ 0.8’’ 3.5’’ 2’’ 0.1’’  In general interferometers better suited (PdB, SMA…  ALMA) APEX: more suited to study « chemistry » than « dynamics »

Molecules detected in planetary atmospheres at mm/submm  ( >100 µm) Venus: CO + isotopes, H 2 O, HDO, SO 2 (?) Mars: CO + isotopes, H 2 O, HDO, H 2 O 2 Jupiter: CO, HCN + isotopes, CS (+C 34 S), H 2 O *, CH 4 Io: SO 2, SO, NaCl Saturn: H 2 O, CH 4 Titan: CO + isotopes, HCN + isotopes, HC 3 N, CH 3 CN, H 2 O, CH 4 Uranus: H 2 O Neptune: CO, HCN, H 2 O Pluto/Triton : none * From space (ISO, Cassini, SWAS, ODIN)

Some goals for APEX Monitor and map H 2 O (and H 2 O 2 ?) in Venus and Mars –HDO 893 GHz ~50 times stronger than at 226 GHz –Mapping: discriminate diurnal vs. temporal variability Search for new species in Venus (e.g. HCl at 1251 GHz, 5 times stronger than at 625 GHz)

Determine location of CO in Saturn and Uranus –In Jupiter, CO has 3 sources (internal, external, SL9) –CO present in both Saturn and Uranus but origin (internal vs. external) unknown –CO 806 GHz ~20 times stronger than at 230 GHz and small beam From Thierry Fouchet

Determine still poorly known stratospheric abundance of methane on Uranus and Neptune –Stratospheric abundance related to injection from troposphere through temperature minimum. Thought to be lower on Uranus due to more sluggish vertical transport –Use CH 4 rotational lines (forbidden but still detected by Cassini on Jupiter, Saturn and Titan)  advantage: little sensitivity to temperature (unlike thermal IR) –Best APEX line: 1256 GHz Titan Cassini/CIRS spectrum

Explore the chemistry of Io’s atmosphere –Search for new (esp. volcanic) species E.g. CO (806 GHz), SiO (651 GHz), ClO (464 GHz), KCl –Determine isotopic ratios in SO 2 (e.g. 936 GHz, 8x stronger than lines at 1mm) Search for isotopic species –E.g. DCN on Titan (  D/H in HCN), 13 CO in Neptune Feasibility TBD SO GHz

Comets General goals of mm/submm observations of comets –Chemical inventory ~20 molecules detected Similarity of composition with ISM ices and molecular hot cores Isotopic ratios (D/H, 12 C/ 13 C, 16 O/ 18 O, 14 N/ 15 N, 32 S /34 S ) Bockelée-Morvan et al. A&A 353, 1101, 2000

Comets –Chemical diversity in comets Diversity among Oort cloud comets No systematic differences between Oort cloud and « Kuiper belt » comets (less CO in Jupiter family comets) Crovisier 2005

Comets –Physics of cometary activity Monitoring of production rates and relative abundances with heliocentric distance (R h ) e.g. HNC/HCN increases with decreasing (R h ) Coma dynamics and physics (extended sources, velocity and temperature conditions in coma) Biver et al 2002

Interest of APEX A Southern telescope ! (  monitoring of inclined objects) Specific goal: D/H ratio

D/H in comets Measured so far only in 3 Oort-cloud comets In H 2 O – Enrichment factor = 12 w.r.t. protosolar value Acquired in presolar cloud? Acquired through ion-molecule reaction in outer cold nebula? Acquired in presolar cloud and reprocessed in inner solar nebula? In other molecules: measured only in DCN/HCN on 1 comet: enrichment factor ~ 100 Need to measure D/H in more comets, especially in short-period comets (could be higher if formed in non-turbulent part of nebula)

HDO detectability in comets TelescopeLineLine area (K km/s) S/N HIFI/Herschel894 GHz2.4 x ALMA241 GHz1.6 x APEX465 GHz4.5 x Q(H 2 O) = 5 x s -1 ; D/H = 3 x Noise estimation: 1h integration, dual polarization ALMA: Tsys = 100 K; APEX: Tsys = 500 K Model :Tgaz = 30 K; Xne = 0.2

Continuum of small bodies ? Size/albedo determination of transneptunian objects from bolometric measurements –Marginally feasible with already available instrumentation (MAMBO, SCUBA) Varuna: 3 sigma detection UB313: 5 sigma detection (Bertoldi et al, Nature, 2 feb 06) –Problem: LABOCA sensitivity does not seem much better LABOCA: typical rms ~ 1.5 mJy/hr at 850 µm ~ SCUBA MAMBO: ~ 0.6 mJy/hr at 1200 µm Object flux varies in  -2 : S/N(MAMBO) ~ S/N (LABOCA) 295 channels: useless for planetary purposes