Astronomers from European Space Agency's Member States are preparing to take part in a French-led mission to be the first to search for rocky planets around other stars. The mission, COROT, is an important stepping stone in the European effort to find habitable, Earth-like planets around other stars.

Artist's impression of the COROT satellite. Credit: CNES/Active Design

COROT will do this by detecting planets as they pass in front of their parent stars, blocking some of the light. From the ground, the only planets detected around other stars have been giant gaseous worlds (Jupiter-like planets), over 10 times the diameter of the Earth. Above the distorting effects of the atmosphere, COROT will be the first spacecraft capable of finding worlds made of rocks, smaller than the gas giants but several times larger than the Earth, itself the biggest rocky planet in the Solar System. Such planets would represent a new, as yet undiscovered, class of world that astronomers believe exists. With COROT, astronomers expect to find between 10-40 of them, together with tens of new gas giants.

In addition, COROT will also be used to detect subtle brightness changes caused by sound waves that resonate through the star. These create a 'starquake' that sends ripples across the star's surface, altering its brightness. The exact nature of the ripples allows astronomers to calculate the star's precise mass, age and chemical composition.

The technique is known as asteroseismology and ESA's Solar and Heliospheric Observatory (SOHO) has been taking similar observations of the Sun for years. So, the COROT data is essential to compare the Sun with other stars.

Instead of being an isolated national mission, ESA's involvement places COROT into the European framework to search for habitable planets. In particular, it will open the door to future missions, Eddington and Darwin.

Illustration of a planet. Credit: ESA/Medialab

Eddington is a maturation of the techniques that COROT will pioneer. It will be a larger telescope, in a more distant orbit, capable of detecting worlds down to half the size of Earth, and it will search for planets around more than 500,000 stars. Eddington, unlike COROT, will also be able to detect habitable planets. In addition it will return precise asteroseismology for 50,000 stars. Launch is planned some time after 2007.

ESA then plans to continue its search for Earth-like worlds into the second decade of the century with the launch of Darwin. This flotilla of eight spacecraft will take pictures of Earth-like worlds, allowing scientists to search for signs of life.

COROT (COnvection ROtation and planetary Transits) is a mission led by the French National Space Agency, CNES. It is a 30-centimetre diameter space telescope designed to detect tiny changes in brightness from nearby stars. Launch is scheduled in 2005 from Russia. ESA joined the mission in October 2000 by agreeing to provide the optics for the telescope and test the payload at its European Space Research and Technology Centre in the Netherlands. As a result of the collaboration, scientists from ESA's Member States will be given access to the satellite's data.