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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
Alla
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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
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.
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