Andrew Morvan Secretary IMechE Young Member’s Panel Devon & Cornwall Branch 11.10.12.
Large Molecules in Comets Dominique Bockelée-Morvan Observatoire de Paris.
-
Upload
winifred-lloyd -
Category
Documents
-
view
216 -
download
2
Transcript of Large Molecules in Comets Dominique Bockelée-Morvan Observatoire de Paris.
Large Molecules in Comets
Dominique Bockelée-Morvan
Observatoire de Paris
What for ? Is it a dream ?
Composition of comets : from small to large species
to understand comet material origin and formationinterstellar condensates ?product of nebular chemistry ?both ?
to constrain Solar System formation to explore the role of comets in the origin of life
Present state : 25 molecules identifiedmost complex species has 10 atomsstill more complex species are suggested
Methods of investigation
Sample return : Stardust on 81P/Wild 2 ….. wait for 2006
Nucleus reflectance spectroscopy (in situ)
Comet atmosphere : parent molecules
Mass spectrometry: Giotto, Stardust missions
IR spectroscopy
Radio spectroscopy
UV
Surface reflectance spectroscopy
Comet 19P/Borrelly
Deep Space 1 mission
2.39 m feature
CN compound ?
Soderblom et al, 2000, Science 296, 1087
Phoebe Saturn’s moonA captured KBO
Cassini/VIMS reflectance spectraH2O, CO2
Organics, nitriles, CN-compoundsClark et al., Nature 435,66, 2005
Mass spectrometryGiotto/Vega results on 1P/Halley Limited by mass resolution Simple species and ion-molecule reaction products H2O, H2CO, H2S, NH3, CH3OH
High molecular mass compounds evidenced from mass spectra tentative identification of e.g, acetic acid, iminoethane, pyridine …Stardust results on Wild 2 : nitrogen rich compounds (Kissel et al. 2004)
Altwegg et al. 1999Sp.Sci. Rev, 90,3
Spectroscopic investigations :gas phase 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
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
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
Radio spectroscopy
19 molecules (not including isotopes, radicals, ions) detected
many first identifications in comets Hyakutake and Hale-Bopp
searching method in Meudon group
PAPSYNTHE code: input: JPL/Cologne spectroscopic databases
comet, telescope characteristics
ouput: expected intensities for all lines
optimisation of receiver tunings, ISM molecules targetted
In Hale Bopp: 10% of the 85-375 GHz window with 3 telescopes
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
Molecular abundances
I glycol
Bockelée-Morvan et al.
Comets II, 2005
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 ?
Sgr B2(N) : glycol/CH3OH = 5 10-4
Hale-Bopp : glycol/CH3OH = 0.1
Analogies with ISM but material formed at high-T is present in comets
(cristalline silicates)
Other evidences for complex species
extended sources of H2CO, CO, HNC
organic grains contribution ?
H2CO : thermodegradation of polyoxymethylene (H2CO polymers)
CO : extended source, if any, not identified
HNC : increased production at decreasing distance from Sun;
origin unkown, HCN polymers ?
Polyoxymethylene (H2CO)n source of H2CO ?
Multiple observational evidences for extended distribution
Steep heliocentric evolution of production rate in comet Hale-Bopp
Laboratory experiments on polyoxymethylene (POM) photo and thermo-degradation
POM thermo-degradation: consistently explain H2CO observations with a few percent POM in grains in mass
Cottin et al. 2004, Icarus 167, 397
Large molecules, source of CO ?
Hale-Bopp : CO in the IR(Disanti et al. 2001)
Hale-Bopp: CO 1.3 and 3mm
(Bockelée-Morvan et al. 2005)
IR suggests CO extended source
Radio mapping at PDB interferometer
=> no extended source
Source of CO, if any: unidentified
Origin of HNC ?
Biver et al. 2002
Biver et al. 2005 Bockelée-Morvan et al. 2005
Hale-Bopp HNC, PdBi
- HNC/HCN increases with decreasing heliocentric distance- HNC and HCN: similar radial distributions at 3 arcsec spatial resolution- production of HNC by chemical reactions excluded- source of HNC in inner coma ?- thermo-degradation of organic material ?
Future prospects for new molecular identifications
current instrumentation : bright comets needed studies are focussing on chemical diversity/spatial distribution ALMA, Herschel Observatory
ALMA: factor 10 increase in sensitivityHerschel : bending modes of PAHs ?
space missions : Deep impact, Rosetta sample return needs for IR spectra of simple organics