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European Exoplanet-Hunting Space Telescope Nears Its End

The French-led mission that discovered the first rocky extrasolar planet is on its last legs
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CNES/D.Ducros

A pioneering European space telescope that discovered the first rocky extrasolar planet is on its last legs, Nature has learned.

According to the French space agency CNES, the Convection, Rotation and Planetary Transits (CoRoT) satellite suffered a computer failure on 2 November. While the spacecraft is still functioning, it can no longer retrieve data from its 30-centimeter telescope, which spots exoplanets by looking for transits — a dimming in brightness as the planet crosses its host star.

“To be frank, I think the problem is serious,” says Fabienne Casoli, the director of space science and exploration at CNES headquarters in Paris.

Launched in 2006, CoRoT set about monitoring thousands of stars. The mission survived its first computer failure in 2009 by relying completely on a second, redundant unit. Casoli says the team has tried several times to reboot the second computer to no avail. The engineering team hasn’t given up on a rescue, and, sometime in December, it will try and reboot the first computer using an alternate power chain. “For the time being, we don’t give up,” she says. “But it is one of the last things we can do.”

In the meantime, Malcolm Fridlund, the project scientist from the European Space Agency, says he’s got plenty of data to work with. He’s preparing a paper that will describe five new exoplanets, bringing the mission’s confirmed count to 31. And there are some 200 candidate exoplanets that remain unconfirmed. “You have to be grateful for what you have,” says Fridlund, who points out that CoRoT had already doubled its three-year design life, and was about to embark on another extension. “It has done what it was designed for and you can’t ask more from a spacecraft.”

As it stands, CoRoT was the first space mission to discover new planets using the transit technique. With its small mirror, it was never a match for the much bigger (and more expensive) 0.95-meter Kepler space telescope, a NASA mission that launched in 2009 and, at latest count, has discovered some 3,000 candidate planets (see “The exoplanet next door”).

But Ronald Gilliland, a Kepler co-investigator at the Pennsylvania State University in State College, says that CoRoT will be judged an “excellent success” for at least two reasons. First, it found that red giant stars oscillated in a way that theorists hadn’t expected, giving astronomers new insight into the structure and evolution of the aging stars. Second, it found CoRoT-7b, the first rocky planet, 1.7 times the diameter of Earth — the first in a whole new category of exoplanets called super-Earths. “It beat the Kepler mission to the punch, so to say, in a few areas,” says Gilliland.

Flying in a 900-kilometer polar orbit, CoRoT has to cope with relatively high doses of radiation and seesawing temperatures at it repeatedly crosses in and out of Earth's shadow. By contrast, the Kepler mission has drifted far from Earth in its own separate orbit around the Sun, a far cleaner radiation environment. Yet it, too, has started to show its age. In July, the Kepler team reported the failure of one of the spacecraft’s four reaction wheels, used to keep the telescope pointed on a fixed region of the sky. On 14 November, NASA announced the end of Kepler’s 3.5-year prime mission, and the start of an extension that could last four years. It will need its three remaining reaction wheels to survive for all of that time in order for the mission to reach a major goal: an Earth-twin orbiting in the habitable zone.

“The reaction wheels are the big worry,” says Gilliland.

This article is reproduced with permission from the magazine Nature. The article was first published on November 16, 2012.

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