A European scientist team working with the COROT (COnvection ROtation and planetary Transits) have discovered an exoplanet orbiting a star slightly more massive than the Sun. Just after 555 days in the orbit, the mission has now observed that more than 50 000 stars and is adding considerably to our knowledge of the basic workings of stars.

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

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

Light-curve of COROT-exo-4b's parent

COROT was launched in December 2006, is the first space-based mission designed to search for exoplanets. Located outside Earth's atmosphere, the satellite is designed to detect rocky exoplanets which are 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 wide ground-based observations.

COROT-exo-4b continuously monitored over several months, the team tracked changes in its brightness between transits. They derived its period of revolution 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 synchronization since their formation must 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.

Labels: COROT finds exoplanet orbiting