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1. A European spacecraft took off today to spearhead the search for another "Earth" among the stars.
2. The Corot space telescope blasted off aboard a Russian Soyuz rocket from the Baikonur cosmodrome in Kazakhstan shortly after 2.20pm.
3. Corot, short for convection rotation and planetary transits, is the first instrument capable of finding small rocky planets beyond the solar system. Any such planet situated in the right orbit stands a good chance of having liquid water on its surface, and quite possibly life, although a leading scientist involved in the project said it was unlikely to find "any little green men".
4. Developed by the French space agency, CNES, and partnered by the European Space Agency (ESA), Austria, Belgium, Germany, Brazil and Spain, Corot will monitor around 120,000 stars with its 27cm telescope from a polar orbit 514 miles above the Earth. Over two and a half years, it will focus on five to six different areas of the sky, measuring the brightness of about 10,000 stars every 512 seconds.
5. "At the present moment we are hoping to find out more about the nature of planets around stars which are potential habitats. We are looking at habitable planets, not inhabited planets. We are not going to find any little green men," Professor Ian Roxburgh, an ESA scientist who has been involved with Corot since its inception, told the BBC Radio 4 Today programme.
6. Prof Roxburgh said it was hoped Corot would find "rocky planets that could develop an atmosphere and, if they are the right distance from their parent star, they could have water".
7. To search for planets, the telescope will look for the dimming of starlight caused when an object passes in front of a star, known as a "transit". Although it will take more sophisticated space telescopes planned in the next 10 years to confirm the presence of an Earth-like planet with oxygen and liquid water, Corot will let scientists know where to point their lenses.
8. Measurements of minute changes in brightness will enable scientists to detect giant Jupiter-like gas planets as well as small rocky ones. It is the rocky planets - that could be no bigger than about twice the size of the Earth—which will cause the most excitement. Scientists expect to find between 10 and 40 of these smaller planets.
9. Corot will also probe into stellar interiors by studying the acoustic waves that ripple across the surface of stars, a technique called "asteroseismology".
10. The nature of the ripples allows astronomers to calculate a star's precise mass, age and chemical composition.
11. "A planet passing in front of a star can be detected by the fall in light from that star. Small oscillations of the star also produce changes in the light emitted, which reveal what the star is made of and how they are structured internally. This data will provide a major boost to our understanding of how stars form and evolve," Prof Roxburgh said.
12. Since the discovery in 1995 of the first "exoplanet"—a planet orbiting a star other than the Sun—more than 200 others have been found by ground-based observatories.
13. Until now the usual method of finding exoplanets has been to detect the "wobble" their gravity imparts on parent stars. But only giant gaseous planets bigger than Jupiter can be found this way, and they are unlikely to harbour life.
14. In the 2010s, ESA plans to launch Darwin, a fleet of four or five interlinked space telescopes that will not only spot small rocky planets, but analyse their atmospheres for signs of biological activity.
15. At around the same time, the US space agency, Nasa, will launch Terrestrial Planet Finder, another space telescope designed to locate Earth-like planets. (615 words)
