Future Ground-based Solar System Research: Synergies with Space Probes and Space Telescopes Portoferraio, Isola d'Elba, Livorno (Italy), September 8-12, 2008 The chemical diversity of comets: synergies between space exploration and ground-based 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 CalTech, Pasadena Allain Manesson Mallet, 1683, “Description de l'Univers”

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”

Crovisier et al. 2008, P&SS, in press Earth-based observations ”figure of merit” Q[H2O] / 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[H2O] / 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 H2O 12 comets with Odin in 2001-2006; also SWAS — Herschel is next

Radio spectroscopy HCN, CH3OH, H2CO, CO, HNC, H2S, CS CSO IRAM CSO (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?

73P/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, ApJ, 675, 931

see talk by Boissier et al. 17P/Holmes Jupiter-family comet huge outburst on 24 October 2007 detected molecules: OH, C, CH3OH, H2CO, HCN, CH3CN, HC3N, H2S, SO, HNC, CS isotopic ratios: C, N, S in HCN, CS, H2S C14N/C15N = 165±40 HC14N/HC15N = 139±26 14N/15N terrestre = 270 Bockelée-Morvan et al. 2008, ApJ, 679, L49 Biver et al. 2008, ACM2008 IRAM interferometer: see talk by Boissier et al.

Isotopic ratios in 17P/Holmes Bockelée-Morvan et al. 2008, ApJ, 679, L49

8P/Tuttle Halley-family comet January 2008 — Δ = 0,25 UA detection of HCN, HNC, CH3OH, CS, H2S, H2CO, CH3CN search for CO and rare species HNCO, HCOOH, SO, HC3N, OCS Biver et al. 2008, ACM2008 In complement : first IR observations of a comet with VLT/CRIRES : studies of H2O, HCN, CH4, C2H2, C2H6, CH3OH Bockelée-Morvan et al. 2008, ACM2008 ; poster by Jehin et al. HNC Biver et al. 2008, ACM2008 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 X5 (Kudo-F.) @ 0.21 AU C/2002 V1 (NEAT) @ 0.11 AU C/2006 P1 (McNaught) @ 0.21 AU Biver et al. 2008, ACM2008, 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

no obvious correlation 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 ground-based 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 Rosetta/MIRO ALMA – see talk by Biver

the end

H2O para ortho