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. BiverD. Bockelée-Morvan, P. Colom

LESIA, Observatoire de ParisJ. Boissier

IRAM, Saint Martin d'HèresD.C. Lis

CalTech, Pasadena

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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 orbitsand their chemical composition ?

Dynamical families of comets (from Levison, 1997)

T = Tisserand parameter

“Oort-cloudcomets”

“Kuiper-beltcomets”

Earth-based

observations

”figure of merit”

Q[H2O] / Δ

roughly proportional

to signal

Crovisier et al. 2008, P&SS, in press

number of moleculesdetected by radio

spectroscopy

as a function of the”figure of merit”

Q[H2O] / Δ

The water production rate of cometsprovides a standard for monitoring cometary activity

and a reference for relative abundances in nucleus ices

indirect measurement18-cm lines of OH at Nançay :

40 comets since 2000

direct measurement557 GHz line of H2O

12 comets with Odin in 2001-2006;also SWAS — Herschel is next

Radio spectroscopy

CSO

HCN, CH3OH, H2CO, CO, HNC, H2S, CS(molecules observed in more than 10 comets)+ rare species and isotopes in a few comets

IRAM

CSO

The inventory of relative abundancesof cometary molecules

Bockelée-Morvan et al. 2005,in Comets II, (with updates)

cumulative histogram:how many molecules remain to be detected?

Spitzer Space Telescope – Reach & Vaubaillon 2006

73P/Schwassmann-Wachmann 3Jupiter-family cometMay 2006 — Δ = 0.08 UAa fragmented cometsimilar compositions for fragments B and Cmethanol depletion

Radio view – Biver et al. 2008, ACM IR view – Dello Russo et al. 2007, Nature, 448, 172

Lis et al. 2008, ApJ, 675, 931

The HNC molecule and the problem of its originvariations of HNC/HCN with helio. distance and among comets

thermal degradation of organic grains?

17P/HolmesJupiter-family comethuge outburston 24 October 2007

detected molecules:OH, C, CH3OH, H2CO, HCN,

CH3CN, HC3N, H2S, SO, HNC, CS

isotopic ratios:C, N, S in HCN, CS, H2SC14N/C15N = 165±40

HC14N/HC15N = 139±2614N/15N terrestre = 270

Bockelée-Morvan et al. 2008, ApJ, 679, L49

Biver et al. 2008, ACM2008

IRAM interferometer:see talk by Boissier et al.

Bockelée-Morvan et al. 2008, ApJ, 679, L49

Isotopic ratios in 17P/Holmes

8P/TuttleHalley-family cometJanuary 2008 — Δ = 0,25 UA

detection of HCN, HNC, CH3OH, CS,

H2S, H2CO, CH3CN

search for CO and rare speciesHNCO, HCOOH, SO, HC3N, OCSBiver et al. 2008, ACM2008

In complement :first IR observations of a cometwith VLT/CRIRES :studies of H2O, HCN, CH4, C2H2, C2H6, CH3OHBockelée-Morvan et al. 2008, ACM2008 ; poster by Jehin et al.

Biver et al. 2008, ACM2008

HNC

also IRAM interferometer:

see talk by Boissier et al.

Comets close to the Sun

- difficult/impossible to observein 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 sublimationand search for refractories

IRAM observations:C/2002 X5 (Kudo-F.) @ 0.21 AUC/2002 V1 (NEAT) @ 0.11 AUC/2006 P1 (McNaught) @ 0.21 AU

Biver et al. 2008, ACM2008, and in preparation rh = 0.12 AU !!

The chemical diversityofcomets from

radio observations

Our preceding study was basedupon ~ 20 comets.

We now have more than30 comets.

Biver et al. 2002, Earth Moon Planets, 90, 323

Crovisier et al. 2008, P&SS, in press

Chemical composition

vs dynamical classes:

no obvious correlation

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...

ALMA – see talk by Biver

Herschel – see talk by Lellouch Rosetta/MIRO

the end

H2O

para ortho