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Caroline Herschel (1750-1848)Caroline Herschel (1750-1848)

one of the first professional women astronomer

she discovered 8 comets

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Odin ISO : water bands

Crovisier et al. 1997Science, 275, 1904

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First observations of rotational lines of water in comets

ISO : C/1995 O1 (Hale-Bopp)

SWAS :C/1999 H1 (Lee)

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Plain line : 557 GHz line of water from ODIN. THICKDashed line : J(3-2) line of HCN from the CSO. THIN

Profiles of thick and thin molecular lines in a comet

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The D/H ratio in comets and in the Solar System

Earth oceans

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Observations of HDO in comets

C/1996 B2 (Hyakutake)CSO

Bockelée-Morvan et al. 1998Icarus 133, 147

C/1995 O1 (Hale-Bopp)JCMT

Meier et al. 1998Science 279, 842

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600 GHz

895 GHz

509 GHz

465 GHz

241 GHz

81 GHzground

HIFI

225 GHz

HDO lines

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16O/18O in comets with ODIN

153P/Ikeya-Zhang: [H2O]/[H218O] = 450 ± 50

C/2001 Q4 (NEAT): [H2O]/[H218O] = 405 ± 35

C/2002 T7 (LINEAR): [H2O]/[H218O] = 510 ± 70

terrestrial ratio: 16O/18O = 499

Lecacheux et al. 2003A&A, 402, L55

Qing-zhu Yin 2004, Science 305, 1729

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Synthetic spectra of water for HIFI and SPIRE.diffraction-limited beam.

Synthetic spectra of water for PACS.beam of 9.4".

Comet at 1 AU from Earth and Sun, temperature = 60 K.

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A spectral survey of a comet with HIFI

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The spectrum of comet Hale-Boppwith water ice features observed with ISO/LWS

Lellouch et al. 1998A&A, 339, L9

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Cometary programmes for Herschel

• Water in comets– Water in a sample of weak comets (HIFI)– Monitoring the water production rate as a function of r (HIFI)– Search for water in distant comets and weakly active objects -

Relation between comets and asteroids. (HIFI)– Investigation of water excitation (HIFI SPIRE PACS)– Measurement of the D/H ratio (from HDO) (HIFI)

• Dust in comets (SPIRE PACS)– correlation between dust and gas– investigation of the SED and search for solid features

• Search for other species (hydrides) (HIFI)– minor species– radicals– ions

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Strategy of observations and scheduling

- Select comets from the catalogue of short-period comets, taking into account

- visibility (solar elongation) - expected activity (from preceding apparitions)- but Q[H2O] < 5. 1028 s-1

- Select unexpected comets as targets of opportunity- they would be the brightest comets- one or two per year with Q[H2O] > 1029 s-1

- notice of a few months, exceptionnally > 1 year

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Some "good" comets for Herschel

8P/Tuttle January 2008Q[H2O] = 3. 1028 s-1 = 0.25 AU

46P/Wirtanen February 2008Q[H2O] = 1. 1028 s-1

85P/Boethin December 2008

Q[H2O] = 3. 1028 s-1 67P/Churyu.-G December 2008 the Rosetta comet

Q[H2O] = 5. 1027 s-1

22P/Kopff May 2009 Q[H2O] = 2.5 1028 s-1

81P/Wild 2 February 2010 the Stardust comet

Q[H2O] = 1.3 1028 s-1

103P/Hartley 2 October 2010

Q[H2O] = 1.2 1028 s-1 = 0.12 AU

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• Principle: combine measurement in visible range with measurement in thermal range determine object’s diameter, albedo, and temperature

• A program currently accomplished by Spitzer• Sensitivity of Herschel probably better than Spitzer, but

much lower than ALMA• Objects typically reachable by Herschel : D ~ 300 km at

40 AU

Photometric measurements of small bodies

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Helschel/SPIRE 250 micrometres

Detectability of TNOs with Herschel/SPIRE