By Rebecca Morelle
Science reporter, BBC News
The hunt for Earth-like planets is to be stepped-up as a new mission prepares for launch.
Corot will be launched just after Christmas (Image: Cnes)
Corot will be the first spacecraft capable of detecting rocky planets just a few times bigger than Earth that are orbiting neighbouring stars.
It will also uncover information on the stars themselves, determining their mass, age and chemical composition.
The multinational mission, led by the French space agency Cnes, is due to launch on 27 December.
Thien Lam Trong, Corot Project Manager from Cnes, said: "Man has been thinking about other worlds since the beginning of astronomy. Corot will help us to understand whether Earth-like exoplanets are a reality or dream."
The 650kg (1,400lb) satellite will be launched on the Soyuz-2-1b vehicle from the Baikonur Cosmodrome, Kazakhstan, into a polar orbit 827km (514 miles) above the Earth.
Corot carries a 27cm (11in) telescope and a four-charge-coupled-device (CCD) camera, sensitive to tiny changes in the brightness of stars.
"There are two main science objectives for this mission," said Ian Roxburgh, professor of astronomy at Queen Mary, University of London, who is the European Space Agency (Esa) scientist on Corot. Esa is a partner on Corot along with Austria, Spain, Germany, Belgium and Brazil.
And one of these, he said, would be to monitor about 60,000 stars to find some of the planets orbiting them.
"As a planet comes inbetween us, the observer, and the star, it goes across the front of the star and blocks out some of the light - this is called a transit, like the transit of Venus.
"So we will be measuring the light from the stars, looking for decreases in brightness to detect if a planet is in orbit."
The spacecraft will detect planets in transit across the stars (Image: Cnes)
Over a period of about 2.5 years, the satellite will focus on five to six different areas of the sky, each time for a duration of about 150 days.
Every 512 seconds, it will measure the brightness of approximately 10,000 stars captured by the onboard camera, which employs the same technology as everyday digital cameras, allowing minute changes in the intensity of their light to be detected.
By measuring these contrasts, the scientists will be able to detect many different types of planets, from huge gaseous ones to small rocky planets. But it is the smaller planets that are of most interest to the team.
While larger planets can be detected from the ground using a variety of techniques, explained Professor Roxburgh, planets nearing Earth's size cannot.
Corot will be the first spacecraft capable of finding them, he said. "We should be able to get down to planets about twice as big as Earth."
The team are expecting to find between 10-40 of these smaller planets and tens of larger gaseous ones in each of the star fields the team observes.
The other part of the mission is to find out more about the stars themselves.
By observing the subtle changes in light created as sound waves ripple through the star - a technique called asteroseismology (similar to seismology, which uses earthquake waves) - the team will be able to find out more about the body's interior and determine its mass, age and chemical composition.
Professor Roxburgh said the team aimed to find out more about 60 of the brightest stars in the area of sky they are observing.
Corot will reveal more about the interior of stars (Image: Cnes)
This, he said, would add to data currently being collected by another Canadian mission, called MOST, which is using a 15cm (6in) telescope aboard a satellite to study the sky.
"Corot will cover a large selection of stars - this is important because you need a good sample of different sorts of stars, with different properties and different ages, in order to understand stellar evolution."
With the data it gains from the mission, particularly relating to Earth-like planets, the team hopes to inform future space research.
In the second decade of this century, Esa plans to launch the Darwin flotilla - a fleet of four or five spacecraft that will hunt for Earth-like planets around other stars and analyse their atmospheres for signs of extra-terrestrial life.
While US space agency Nasa is to launch a Terrestrial Planet Finder (TPF) mission which will also aim to locate Earth-like worlds.
Professor Roxburgh told the BBC News website: "Corot is a pioneer as far as planets are concerned.
"It will enable us to get knowledge of the sorts of stars that have planets and that sort of information will be needed for the next generation of missions searching for signs of habitable planets."
1. 4CCD camera and electronics: captures tiny variations in stars' brightness
2. Baffle: shields telescope lens from light pollution
3. Telescope: views the star fields
4. Proteus platform: contains communication equipment, temperature controls and direction controls
5. Solar panel: the Sun's radiation is a source of power for the satellite