A French-designed satellite was put in orbit yesterday on the first space-based mission to seek planets with Earth-like conditions that could sustain life beyond the solar system.

A Russian Soyuz rocket put Corot, a 300kg (660lb) craft with a 12-inch telescope and two cameras, in an orbit of 500 miles altitude passing over the Earth’s poles. The satellite, designed by the French national space agency and supported by the European Space Agency, is to monitor 120,000 stars during its 30-month mission.

This should enable it to find many as yet unknown planets. Ground-based observatories have already discovered more than 200 “exoplanets” outside the solar system.

“Corot will be able to find extra-solar planets of all sizes and natures, contrary to what we can do from the ground at the moment,” said Claude Catala, a researcher on the project. “We expect to obtain a better vision of planet systems beyond the solar system,” she said. “Ultimately it will allow us to estimate the likelihood of there existing planets resembling the Earth in the neighbourhood of the Sun or further away in the galaxy.”

Corot, whose name is both that of Jean-Baptiste Corot, the painter, and an acronym (convection, rotation, transit), will be able to detect planets by monitoring changes in the light from their suns. It will also study the mechanics of stars, the nearest of which is 4,000 light years from the Earth.

A US probe, called Kepler, is to be launched at the end of 2008 on a similar mission but with more powerful instruments on board.

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