- Slides: 20
The chemical diversity of comets: synergies between space exploration and groundbased radio observations J. Crovisier, N. Biver D. Bockelée-Morvan, P. Colom LESIA, Observatoire de Paris J. Boissier IRAM, Saint Martin d'Hères D. C. Lis Cal. Tech, Pasadena Allain Manesson Mallet, 1683, “Description de l'Univers” Future Ground-based Solar System Research: Synergies with Space Probes and Space Telescopes Portoferraio, Isola d'Elba, Livorno (Italy), September 8 -12, 2008
Fundamental questions on comets What are comets ? What is their composition ? How do they work ? What is their role in the Solar System ? How did they form ? How did they evolve ? What is their relationship with other small bodies ? Is there a relation between their orbits and their chemical composition ?
Dynamical families of comets (from Levison, 1997) T = Tisserand parameter “Oort-cloud comets” “Kuiper-belt comets”
Earth-based observations ”figure of merit” Q[H 2 O] / Δ roughly proportional to signal Crovisier et al. 2008, P&SS, in press
number of molecules detected by radio spectroscopy as a function of the ”figure of merit” Q[H 2 O] / Δ
The water production rate of comets provides a standard for monitoring cometary activity and a reference for relative abundances in nucleus ices indirect measurement 18 -cm lines of OH at Nançay : 40 comets since 2000 direct measurement 557 GHz line of H 2 O 12 comets with Odin in 2001 -2006; also SWAS — Herschel is next
IRAM Radio spectroscopy CSO HCN, CH 3 OH, H 2 CO, HNC, H 2 S, CS (molecules observed in more than 10 comets) + rare species and isotopes in a few comets CSO
The inventory of relative abundances of cometary molecules Bockelée-Morvan et al. 2005, in Comets II, (with updates) cumulative histogram: how many molecules remain to be detected?
73 P/Schwassmann-Wachmann 3 Jupiter-family comet May 2006 — Δ = 0. 08 UA a fragmented comet similar compositions for fragments B and C methanol depletion Spitzer Space Telescope – Reach & Vaubaillon 2006 Radio view – Biver et al. 2008, ACM IR view – Dello Russo et al. 2007, Nature, 448, 172
The HNC molecule and the problem of its origin variations of HNC/HCN with helio. distance and among comets thermal degradation of organic grains? Lis et al. 2008, Ap. J, 675, 931
17 P/Holmes Jupiter-family comet huge outburst on 24 October 2007 detected molecules: OH, C, CH 3 OH, H 2 CO, HCN, CH 3 CN, HC 3 N, H 2 S, SO, HNC, CS isotopic ratios: C, N, S in HCN, CS, H 2 S C 14 N/C 15 N = 165± 40 HC 14 N/HC 15 N = 139± 26 14 N/15 N terrestre = 270 Biver et al. 2008, ACM 2008 Bockelée-Morvan et al. 2008, Ap. J, 679, L 49 IRAM interferometer: see talk by Boissier et al.
Isotopic ratios in 17 P/Holmes Bockelée-Morvan et al. 2008, Ap. J, 679, L 49
8 P/Tuttle Halley-family comet January 2008 — Δ = 0, 25 UA detection of HCN, HNC, CH 3 OH, CS, H 2 CO, CH 3 CN search for CO and rare species HNCO, HCOOH, SO, HC 3 N, OCS HNC Biver et al. 2008, ACM 2008 In complement : first IR observations of a comet with VLT/CRIRES : studies of H 2 O, HCN, CH 4, C 2 H 2, C 2 H 6, CH 3 OH Biver et al. 2008, ACM 2008 Bockelée-Morvan et al. 2008, ACM 2008 ; poster by Jehin et al. also IRAM interferometer: see talk by Boissier et al.
Comets close to the Sun - difficult/impossible to observe in the visible/IR or with spacecraft (except coronagraphs) - possible with some radio telescopes rh < 0. 20 AU ==> solar elong. < 11. 5° allows investigation of - gas velocity and temperature - specific mechanisms (e. g. photolysis shielding) - high-temperature sublimation and search for refractories IRAM observations: C/2002 X 5 (Kudo-F. ) @ 0. 21 AU C/2002 V 1 (NEAT) @ 0. 11 AU C/2006 P 1 (Mc. Naught) @ 0. 21 AU Biver et al. 2008, ACM 2008, and in preparation rh = 0. 12 AU !!
The chemical diversity ofcomets from radio observations Our preceding study was based upon ~ 20 comets. We now have more than 30 comets. Biver et al. 2002, Earth Moon Planets, 90, 323
Chemical composition vs dynamical classes: no obvious correlation Crovisier et al. 2008, P&SS, in press
Conclusions • The cometary diversity can only be studied by large groundbased or Earth-orbit observing programmes. Space exploration accesses only a limited number of objects (short-period comets). • Radio spectroscopy (as well as visible and IR spectroscopy) reveals a broad chemical diversity among comets. • There is no obvious correlation between chemical diversity and the dynamical classes of comets.
Prospects with new facilities. . . Herschel – see talk by Lellouch ALMA – see talk by Biver Rosetta/MIRO
H 2 O para ortho