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, 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 frequenciese.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/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 Pluto10-60’’ 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, 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)

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)

• 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 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/CIRSspectrum

• 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

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

Comets

– Chemical diversity

in comets

Diversity among Oort cloudcomets

No systematic differencesbetween 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 (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

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 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)

HDO detectability in comets

Telescope Line Line area

(K km/s)

S/N

HIFI/Herschel 894 GHz 2.4 x 10-2 4

ALMA 241 GHz 1.6 x 10-4 0.3

APEX 465 GHz 4.5 x 10-2 2.7

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 KModel :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