1. Thanks Pierre ! CO HCN CxHyOzNw me Molecules in galaxies
Molecules in ISM
Molecules in comets

2. Molecules in comets Dominique Bockelée-Morvan Observatoire de Paris

3. 1864 first spectrum of a comet (Donati, comet Tempel C/1864 N1)
1868 identification of carbon and Swan bands C2 (Huggins)
1881 identification of Na, other emissions of CH, CN, C2, C3 (comet Cruls-Tebbutt 1881III)
1911 indentification of CO+ by de la Baume Pluvinel and Baldet (comet Morehouse 1908III)
1941 idendification of OH (comet Cunningham 1941I)

4. De la Baume and Baldet (1911)C2
CO+ CN

5. Hunt for molecules in comets (spectroscopy)
Visible and UV windows: essentially radicals and ions
exceptions : CO and S2
tentative detection of phenanthene and pyrene in 1P/Halley
IR 2-5 mm window : fundamental bands of vibration
hot bands of water (e.g., n3-n2)
emission process : fluorescence
radio window (cm to submm): privileged tool
cold atmospheres

6. A typical optical/near-IR comet spectrum
109P/Swift-Tuttle
Feldman et al. (2005)

7. UV cometary spectra HST spectra of C/1996 B2 (Hyakutake)
FUSE spectrum of C/2001 A2 (LINEAR)
Feldman et al. (2002)
Weaver et al. (1998)

8. Possible idendification of phenanthrene C14H10
TKS/Vega
@450 km
1P/Halley
Q/Q(H2O) = 1.5x10-3
Comparaison with
laser-induced fluorescence
spectra /jet-cooled conditions
Moreels et al. A&A 282, 643
Possible identification of pyrene C16H10 : C16H10 / C14H10 = 0.04
(Clairemidi et al. PSS 52, 761, 2004)
PAHs, if present, are released from grains (Joblin et al PSS 45)

9. Hunt for molecules in comets (spectroscopy)
Visible and UV windows: essentially radicals and ions
exceptions : CO and S2
tentative detection of phenanthene and pyrene in 1P/Halley
IR 2-5 mm window : fundamental bands of vibration
hot bands of water (e.g., n3-n2)
emission process : fluorescence
radio window (cm to submm): privileged tool
cold atmospheres

11. IR spectroscopy Simple species : H2O, CO, CO2, H2CO, CH3OH
IKS/VEGA
Combes et al. (1986)
Simple species : H2O, CO, CO2, H2CO, CH3OH
mm band : CH-bearing species in gas phase
unidentified compounds at 3.42mm
3.28 mm band: PAHs ?
PAHs bands at higher wavelengths not seen in
Hale-Bopp ISO spectra

12. IR spectroscopy High spectral resolution ro-vibrational lines of
CH4, C2H2, C2H6
CH3OH, HCN
Unidentified lines
need for detailed ro-vibrational
structure and strength of
CH3OH bands in 3 mm region
+ other organic species
C/1999 H1 (Lee) Keck/NIRSPEC Mumma et al. (2001)

13. Hunt for molecules in comets (spectroscopy)
Visible and UV windows: essentially radicals and ions
exceptions : CO and S2
tentative detection of phenanthene and pyrene in 1P/Halley
IR 2-5 mm window : fundamental bands of vibration
hot bands of water (e.g., n3-n2)
emission process : fluorescence
radio window (cm to submm): privileged tool
cold atmospheres

14. Radio spectroscopy OH 18cm lines (1973, comet Kohoutek, Nançay)
HCN 89 GHz (1985, comet Halley, IRAM 30-m)
19 molecules (not including isotopes, radicals, ions) now detected
many first identifications in comets Hyakutake and Hale-Bopp
(in Hale Bopp: 10% of the GHz window with IRAM 30m, PdBi and CSO)
Isotopes: HDO, DCN, H13CN, HC15N, C34S, H234S
Radicals and ions: NS, CS, SO, CN, H3O+ ,CO+

15. Historical radio spectra of comets
First OH 18 cm detection (Nançay)
Comet Kohoutek, Biraud et al. (1974)
HCN J(1-0) detection (IRAM 30-m)
Comet Halley, Despois et al. (1986)

17. New molecules in Hale-Bopp
GHz
Crovisier et al. 2004
A&A 418, L35, 2004
Ethylene glycol HOCH2CH2OH
11 lines identified in 2003 when
frequencies available in Cologne
database
Bockelée-Morvan et al.
A&A 353, 1101, 2000

18. (cf N. Biver talk, tomorrow)
H2O
Odin observations
H2O, H218O and NH3
C/2001 Q4 (NEAT)
H218O
NH3
(cf N. Biver talk, tomorrow)

19. Evidence for chemical diversity Crovisier 2005
Diversity among Oort cloud
comets
No systematic differences
between Oort cloud and
« Kuiper belt » comets
Crovisier 2005

20. Upper limits for complex species
Crovisier et al. A&A 418, 1141,2004

21. Molecular complexity cyanopolyynes but CH4 ~ C2H2 ~ C2H6
abundancesm when complexity k
C2H5OH/CH3OH <1/25
cyanopolyynes
but CH4 ~ C2H2 ~ C2H6
reduced alcohols wrt aldehydes
CH3OH > H2CO
OHCH2CH2OH > CH2OHCHO
Grain surface reactions ?
Crovisier et al. A&A 418, 1141,2004

22. Deuterium in comets Atomic D detected (HST) In H2O: D/H = 3 10-4
In HCN: D/H =
Atomic D detected (HST)
In CH3OH, H2CO, NH3, CH4:
upper limits of 10-2 to a few 10-2
C/1996B2 Hyakutake
CSO
Bockelée-Morvan et al. (1998)
JCMT
Meier et al. (1998)

23. Isotopic ratios

24. Ortho-para ratios Why are all these temperatures similar?
Table from Kawakita et al. 2004, ApJ 601, 1152
Recent results
C/2001 Q4 (NEAT) methane Tspin = 33±3 K Kawakita et al. 2005, ApJ 623, L49
C/1999 S4 (LINEAR) water Tspin > 30 K Dello Russo et al. 2005, ApJ 621, 537
C/1999 H1 (Lee) water Tspin ≈ 30 K idem
C/2001 A2 (LINEAR) water Tspin = 23±4 K idem
Why are all these temperatures similar?
What is their signification?

25. What new from Deep Impact ?
A’Hearn et al Sciencexpress
Deep Impact spectra : large increase in the amount of organics compared to water
9P/Tempel 1, 4 July
4.9 x 7.6 km dark nucleus with low thermal inertia, low density, negligible strength
smooth and rough terrains, natural impact craters
DI impact: fine dust ejected, no dramatic increase in gas production (see Biver talk)
Keller et al Sciencexpress

26. Strong increase in silicate emission after impact
Numerous bands reported : Al2O3, PAHs, smectite clay, carbonates ….

27. PUB Deep Impact : les premiers resultats Olivier Groussin
Observatoire de Meudon
Lundi 7 Novembre
11H

28. Open questions in comet chemistry
a lot of lines still unidentified
some radicals remain orphans : e.g. C3, NS
origin of HNC : coma or nucleus product
origin of CN ?
nature of distributed sources of H2CO and CO
nature of dust organics ?
How abundances in the coma are related to abundances in the nucleus ?
(chemical differenciation in the nucleus)
degree of compositional heterogeneity in comet nuclei

29. What the composition tells us about the origin of comet material?
molecular composition present analogies with composition of star forming regions and interstellar ices
D/H ratios kept interstellar signatures
unequilibrated ortho/para ratios
low-T formation
(grain surface, ion-molecule processes)
highly processed material is present however (cristalline silicates)
mixing with nebular products
Chemical diversity in comets : how to explain it ?

30. Future prospects current instrumentation : bright comets needed
studies are focussing on chemical diversity/spatial distribution
ALMA : factor 10 increase in sensitivity
large uv-coverage, instantaneous maps
Herschel Observatory: water, D/H ratio, bending modes of PAHs ?
Space missions : Deep impact, Rosetta