1. 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”

2. 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 ?

3. Dynamical families of comets (from Levison, 1997)‏
T = Tisserand‏ parameter
“Oort-cloud
comets”
“Kuiper-belt
comets”

4. 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

5. number of molecules
detected by radio
spectroscopy
as a function of the
”figure of merit”
Q[H2O] / Δ

6. 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 ;
also SWAS — Herschel is next

7. 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

8. 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?

9. 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

10. 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

11. 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.

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

13. 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.

14. 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 !!

15. 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

16. no obvious correlation
Chemical composition
vs dynamical classes:
no obvious correlation
Crovisier et al. 2008, P&SS, in press

17. 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.

18. Prospects with new facilities... Herschel – see talk by Lellouch
Rosetta/MIRO
ALMA – see talk by Biver

19. the end

20. H2O
para
ortho