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Posted by baalke on October 10, 2007, 5:14 pm
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http://www.esa.int/esaSC/SEMF8BV7D7F_index_0.html
New isotope molecule may add to Venus' greenhouse effect
European Space Agency
10 October 2007
Planetary scientists on both sides of the Atlantic have tracked down a
rare
molecule in the atmospheres of both Mars and Venus. The molecule, an
exotic
form of carbon dioxide, could affect the way the greenhouse mechanism
works
on Venus.
The discovery is being announced today at the annual meeting of the
American
Astronomical Society's Division of Planetary Sciences in Orlando,
Florida.
Its presence could affect the way the greenhouse mechanism works on
Venus.
The mystery began back in April 2006, soon after ESA's Venus Express
arrived
at the second planet in the Solar System.
A European team including members from France, Belgium and Russia lead
by
Jean-Loup Bertaux, Service d'Aeronomie du CNRS, France and Ann-Carine
Vandaele, Institut d'Aeronomie Spatiale de Belgique, were using their
Infrared Atmospheric Spectrometer (SOIR) instrument to measure solar
occultations.
To do this, the instrument watches the Sun set behind Venus, allowing
the
scientists to study the way specific wavelengths of light are absorbed
by
the planet's atmosphere. These wavelengths and the level of absorption
then
give away the identity and amount of gases in the atmosphere.
The team saw an unidentified signature at 3.3 micrometres in the
mid-infrared region of the spectrum. "It was conspicuous and
systematic,
increasing with depth in the atmosphere during the occultation, so we
knew
it was real," says Bertaux.
The team kept their discovery confidential as they attempted to
identify the
molecule responsible. They thought at first that it must be an
organic
molecule. These molecules contain carbon and hydrogen. However, none
of the
known organic molecules fitted well with the observations.
Then, in December 2006, Mike Mumma of NASA's Goddard Space Flight
Center,
Maryland, enquired whether the SOIR team was seeing anything special
on
Venus at 3.3 microns. He had discovered an unidentified spectral
signature
at that wavelength using telescopes on Hawaii pointing at Mars. The
two
teams compared the absorption signatures: they were identical.
This was a big clue. Both the atmospheres of Mars and Venus are
composed of
95% carbon dioxide, although Venus's atmosphere is much thicker than
the one
at Mars. The American team suggested that the signature could be
coming from
an isotope of carbon dioxide, where one oxygen atom is 'normal', with
eight
protons and eight neutrons, while the other has eight protons and ten
neutrons. Such an isotope makes up about 1% of carbon dioxide on
Earth, the
rest contains two normal oxygen atoms.
However, no one had previously seen the molecule absorb at 3.3
micrometres.
An investigation by three independent groups, one led by Mumma in
America,
Sergei Tashkun and Valery Perevalov at Tomsk State University, Russia,
and
Richard Dahoo at Service d'Aeronomie du CNRS, France, all came to the
same
conclusion. The signature could be caused by a rare transition only
possible
in the isotope.
The different weights of the oxygen atoms allow the molecule to alter
its
vibration in two ways simultaneously, whereas normal molecules can
only
change one state at a time.
This rare transition allows it to absorb even more energy and so
contribute
even more to the greenhouse effect on Venus. On Earth, however, there
is 250
000 times less carbon dioxide so its additional contribution to our
greenhouse effect will be small.
Notes for Editors:
The findings appear in: 'First Observation of 628 CO2 isotopologue
band at
3.3 micrometres in the atmosphere of Venus by solar occultation from
Venus
Express' by J-L Bertaux, A. C. Vandaele, V. Wilquet, F. Montmessin,
R.
Dahoo, E. Villard, O. Korablev, A. Fedorova.
For more information:
Jean-Loup Bertaux, Service d'aeronomie du CNRS, France
Email: Jean-Loup.Bertaux@aerov.jussieu.fr
Ann Carine Vandaele, The Belgian Institute for Space Aeronomy
Email: A-C.Vandaele@aeronomie.be
Michael Mumma, NASA Goddard Space Flight Center, USA
Email: Michael.J.Mumma@nasa.gov
ESA PIO source:
Monica Talevi
Science Information Manager
ESA - Communication Dept.
Tel: +31 71 565 3223
Fax: +31 71 565 4101
Email: Monica.Talevi@esa.int
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