The context
Comets are small icy planetesimals formed in the outer solar system.
The nucleus, typically a few kilometers in diameter, is
essentially constituted of water ice mixed with carbon oxides, methane,
ammonia, and of dust particles. When the comet approaches the Sun, the
ices sublimate, forming a gaseous and dusty coma. Radiation and solar
wind blow this material to form the spectacular cometary tails.
Because comets are thought to be remnants of the early stages of the
solar system, they are considered as the most pristine solar system
bodies. Understanding their origin, evolution ans composition is a clue
to the history of our solar system. Moreover comets contain complex
organic molecules, and may play a key role in the transfer of water and
organics from the interstellar medium to the early Earth, then
contributing to the origin of life.
Recent work and projects
We have started a systematic study of comets using high-resolution
spectroscopy with the Ultraviolet Visible Echelle Spectrograph (UVES)
of the ESO Very Large Telescope (VLT) located in the Paranal Observatory
. Thanks to the high throughput of
the instrument, faint comets can now be investigated, namely to
identify the spectral signature of new species, to determine chemical
compositions and isotope ratios, as well as spin temperatures via
ortho-to-para molecular ratios. Part of this research is done in
collaboration with the McDonald Observatory Planetary Systems group, the Besançon
Observatory,
the European
Space Agency
and the Leiden
Observatory.
First focusing on the measurement of the carbon 12C /13C
and nitrogen 14N /15N
isotope
ratios in various comets at small and high heliocentric distances, we
found surprisingly low 14N /15N isotope ratios
from the CN radical, a
possibly key ingredient to prebiotic chemistry. Our observations
suggest the existence of several sources of cometary CN with very
different isotope ratios. A few pictures
illustrate the method.
These studies should be extended during the Deep
Impact Space Mission. On July 4, 2005 Comet Tempel 1 will be
impacted by a 370 kg mass which should eject ice and dust debris from
below the comet surface, revealing for the first time fresh unaltered
material. The impact will produce a brightening of the comet,
making it observable from the ground. Using the VLT UVES
spectrograph, we will obtain high-resolution spectra before and after
the event to measure isotopic ratios and determine spectral changes
possibly revealing new species.
Publications
Preprints
(astro-ph)
All
publications
since 2000 (ADS)
Publications in
refereed journals since 1995
Press releases
14.09.2003
- Space Flight Now - Europe opens new window to our origins
12.09.2003
- ULG - Les
comètes sont-elles à l'origine de la vie sur Terre?
12.09.2003
- ESO-PR - Optical
Detection of Anomalous Nitrogen in Comets
21.05.2001
- APOD - Another
Comet LINEAR breaks up
18.05.2001
- ESO-PR - Comet
LINEAR splits further
| Home | Publications
| People
| Teaching | Pictures | Links
|