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

Molecules in comets Dominique Bockelée-Morvan Observatoire de Paris

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)

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

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

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

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)

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. 1997 PSS 45)

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

IR spectroscopy Simple species : H2O, CO, CO2, H2CO, CH3OH IKS/VEGA Combes et al. (1986) Simple species : H2O, CO, CO2, H2CO, CH3OH 3.3-3.5 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

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)

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

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 85-375 GHz window with IRAM 30m, PdBi and CSO) Isotopes: HDO, DCN, H13CN, HC15N, C34S, H234S Radicals and ions: NS, CS, SO, CN, H3O+ ,CO+

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)

New molecules in Hale-Bopp 230.578 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

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

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

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

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

Deuterium in comets Atomic D detected (HST) In H2O: D/H = 3 10-4 In HCN: D/H = 2.3 10-3 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)

Isotopic ratios

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?

What new from Deep Impact ? A’Hearn et al. 2005 Sciencexpress Deep Impact spectra : large increase in the amount of organics compared to water 9P/Tempel 1, 4 July 4 2005 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. 2005 Sciencexpress

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

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

Open questions in comet chemistry HNC@PdBi 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

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 ?

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