CO HCN CO HCN

CxHyOzNw

Thanks Pierre !

Molecules in galaxiesMolecules in ISMMolecules in comets

me

Molecules in comets

Dominique Bockelée-MorvanObservatoire 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)

C2 CNCO+

De la Baume and Baldet (1911)

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 m window : fundamental bands of vibration

hot bands of water (e.g., 3-2)

emission process : fluorescence

radio window (cm to submm): privileged tool

cold atmospheres

Feldman et al. (2005)

109P/Swift-Tuttle

A typical optical/near-IR comet spectrum

UV cometary spectraHST spectra of C/1996 B2 (Hyakutake) FUSE spectrum of C/2001 A2 (LINEAR)

Weaver et al. (1998)

Feldman et al. (2002)

Possible idendification of phenanthrene C14H10

TKS/Vega@450 km1P/Halley

Q/Q(H2O) = 1.5x10-3

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)

Comparaison with laser-induced fluorescencespectra /jet-cooled conditions

Visible and UV windows: essentially radicals and ions

exceptions : CO and S2

tentative detection of phenanthene and pyrene in 1P/Halley

IR 2-5 m window : fundamental bands of vibration

hot bands of water (e.g., 3-2)

emission process : fluorescence

radio window (cm to submm): privileged tool

cold atmospheres

Hunt for molecules in comets(spectroscopy)

IR spectroscopy

Combes et al. (1986)

IKS/VEGA

Simple species : H2O, CO, CO2, H2CO, CH3OH3.3-3.5 m band : CH-bearing species in gas phase unidentified compounds at 3.42m 3.28 m band: PAHs ? PAHs bands at higher wavelengths not seen in Hale-Bopp ISO spectra

IR spectroscopy

C/1999 H1 (Lee) Keck/NIRSPEC Mumma et al. (2001)

High spectral resolutionro-vibrational lines ofCH4, C2H2, C2H6

CH3OH, HCN

Unidentified lines

need for detailed ro-vibrationalstructure and strength of CH3OH bands in 3 m region+ other organic species

Visible and UV windows: essentially radicals and ions

exceptions : CO and S2

tentative detection of phenanthene and pyrene in 1P/Halley

IR 2-5 m window : fundamental bands of vibration

hot bands of water (e.g., 3-2)

emission process : fluorescence

radio window (cm to submm): privileged tool

cold atmospheres

Hunt for molecules in comets(spectroscopy)

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)

Bockelée-Morvan et al. A&A 353, 1101, 2000

Crovisier et al. 2004A&A 418, L35, 2004

Ethylene glycol HOCH2CH2OH11 lines identified in 2003 whenfrequencies available in Colognedatabase

230.578 GHz

New molecules in Hale-Bopp

Odin observations

H2O, H218O and NH3

C/2001 Q4 (NEAT)

H2O

H218O

NH3(cf N. Biver talk, tomorrow)

Crovisier 2005

Evidence for chemicaldiversity Diversity among Oort cloudcomets

No systematic differencesbetween Oort cloud and

« Kuiper belt » comets

Upper limits for complex species

Crovisier et al. A&A 418, 1141,2004

Molecular complexity

Crovisier et al. A&A 418, 1141,2004

abundances when complexity

C2H5OH/CH3OH <1/25

cyanopolyynes

but CH4 ~ C2H2 ~ C2H6

reduced alcohols wrt aldehydes

CH3OH > H2CO

OHCH2CH2OH > CH2OHCHO

Grain surface reactions ?

Deuterium in comets

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

Bockelée-Morvan et al. (1998)

Meier et al. (1998)

C/1996B2 HyakutakeCSO

JCMT

Isotopic ratios

Recent resultsC/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?

Table from Kawakita et al. 2004, ApJ 601, 1152

Ortho-para ratios

What new from Deep Impact ?

A’Hearn et al. 2005 Sciencexpress

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)

Deep Impact spectra : large increase in the amount of organics compared to water

Keller et al. 2005 Sciencexpress

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

Deep Impact : les premiers resultats

Olivier Groussin

Observatoire de Meudon

Lundi 7 Novembre

11H

PUB

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

HNC@PdBi

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