ESA News
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24 July 2008

COROT finds exoplanet orbiting Sun-like star

A team of European scientists working with COROT have discovered an
exoplanet orbiting a star slightly more massive than the Sun. After just 555
days in orbit, the mission has now observed more than 50 000 stars and is
adding significantly to our knowledge of the fundamental workings of stars.

The latest discovery, COROT-exo-4b is an exoplanet of about the same size as
Jupiter. It takes 9.2 days to orbit its star, the second longest period for
any transiting exoplanet ever found.

The team has found that the star, which is slightly larger than our Sun, is
rotating at the same pace as the planet's period of revolution. This is
quite a surprise for the team, as the planet is thought to be too low in
mass and too distant from its star, for the star to have any major influence
on its rotation.

Launched in December 2006, COROT is the first space-based mission designed
to search for exoplanets. Located outside Earth's atmosphere, the satellite
is designed to detect rocky exoplanets almost as small as Earth. The
satellite uses transits, the tiny dips in the light output from a star when
a planet passes in front of it, to detect and study planets. This is
followed up by extensive ground-based observations.

Monitoring COROT-exo-4b continuously over several months, the team tracked
variations in its brightness between transits. They derived its period of
rotation by monitoring dark spots on its surface that rotated in and out of
view.

It is not known whether COROT-exo-4b and its star have always been rotating
in sync since their formation about 1000 million years ago, or if the star's
rotation synchronized later. Studying such systems with COROT will help
scientists gain valuable insight into star-planet interactions.

This is the first transiting exoplanet found with such a peculiar
combination of mass and period of rotation. There is surely something
special about how it formed and evolved.

Notes for editors:
 
This discovery is being presented today at the Cool Stars 15 meeting at St
Andrews University.

The ground-based follow-up of the detection of COROT-exo-4b was carried out
with the cross-dispersed echelle spectrograph, SOPHIE, on the 1.8-m
telescope at the Observatoire de Haute Provence (France), the High Accuracy
Radial velocity Planet Searcher, HARPS on the 3.6-m telescope at La Silla
observatory (Chile) and the cross-dispersed echelle spectrograph, UVES on
the 8.2-m Very Large Telescope at Paranal (Chile), the 1-m telescope at the
Wise Observatory in Israel, the 1-m Euler telescope at La Silla, and the
3.6-m Canada-France-Hawaii telescope.

COROT is a CNES project with ESA participation. The other major partners in
this mission are Austria, Belgium, Brazil, Germany and Spain.

For more information:
 
Malcolm Fridlund, ESA COROT Project Scientist
Email: Malcolm.Fridlund {at} esa.int

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