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Solar System observations with APEX

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

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Solar System observations with APEX

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

  2. 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, Tsys 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

  3. Areas • Planetary atmospheres • Cometary atmospheres • Small bodies (continuum) ??

  4. Planetary atmospheres at mm/submmwavelengths • 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 »

  5. Molecules detected in planetary atmospheres at mm/submm (>100µm) Venus: CO + isotopes, H2O, HDO, SO2 (?) Mars: CO + isotopes, H2O, HDO, H2O2 Jupiter: CO, HCN + isotopes, CS (+C34S), H2O*, CH4 Io: SO2, SO, NaCl Saturn: H2O, CH4 Titan: CO + isotopes, HCN + isotopes, HC3N, CH3CN, H2O, CH4 Uranus: H2O Neptune: CO, HCN, H2O Pluto/Triton : none * From space (ISO, Cassini, SWAS, ODIN)

  6. Some goals for APEX • Monitor and map H2O (and H2O2 ?) 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)

  7. 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

  8. 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 CH4 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

  9. 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 SO2 (e.g. 936 GHz, 8x stronger than lines at 1mm) • Search for isotopic species • E.g. DCN on Titan ( D/H in HCN), 13CO in Neptune • Feasibility TBD SO2 221.965 GHz

  10. 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, 12C/13C, 16O/18O, 14N/15N, 32S/34S) Bockelée-Morvan et al. A&A 353, 1101, 2000

  11. 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

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

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

  14. D/H in comets • Measured so far only in 3 Oort-cloud comets • In H2O • 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)

  15. HDO detectability in comets Q(H2O) = 5 x 1028 s-1; D/H = 3 x 10-4 Noise estimation:1h integration, dual polarization ALMA: Tsys = 100 K; APEX: Tsys = 500 K Model :Tgaz = 30 K; Xne = 0.2

  16. 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

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