It may take a little longer to find Earth-like planets than astronomers had hoped, due to a glitch on NASA鈥檚 Kepler spacecraft. But the mission is far from blind to such worlds, says the mission鈥檚 chief scientist.
launched in March to search for life-friendly planets around other stars. It does this by looking for slight dips in a star鈥檚 brightness that occur when a planet passes in front of the star, an event called a transit.
In August, the Kepler team announced that the spacecraft had detected a previously known gas giant planet, confirming its ability to spot alien worlds.
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But the mission鈥檚 ultimate goal is to find Earth-size planets at the right distances from their parent stars to be able to have liquid water on their surfaces, making them potential abodes for life.
Faulty light detectors on the spacecraft will make that task a little more difficult than expected, the mission鈥檚 chief scientist told a NASA advisory committee on Thursday, a development first by Nature News.
Kepler focuses light onto 42 light-detecting chips, called CCDs, each of which monitors stars in a different part of the telescope鈥檚 field of view. Each CCD is split into two for the purposes of sending data back to Earth, for a total of 84 data channels.
Flickering stars
Three of these channels are plagued by electronic noise that makes stars in their field of view appear to flicker 鈥� 鈥渓ike it鈥檚 changing its brightness at a rapid rate鈥�, says Kepler chief scientist William Borucki of NASA鈥檚 Ames Research Center in Moffett Field, California.
The tiny brightness dips from a transiting Earth-size planet could be lost amid these fluctuations. But since the problem affects only a few of the 84 channels, it is not expected to hide all Earth-size planets, Borucki says.
鈥淧eople have found a pimple here and they are trying to make it into a mountain,鈥� he told New 杏吧原创. 鈥淎 lot of the planets will show up regardless.鈥�
Software fix
Still, the first discovery of a habitable Earth-size exoplanet could be delayed if it happens to orbit a star monitored by one of the noisy detectors, Borucki admits.
The team is developing software to automatically remove the noise from data after it is sent down to Earth, but rigorous testing means it will not be ready until 2011.
Astronomers require three transits to be sure they have detected a planet. So even without this glitch, it would take until at least 2012 to confirm Earth鈥檚 first twins, as they would also circle their host stars in one-year orbits.
Small, cool stars
The delays would only affect habitable planets around smaller, cooler stars. The habitable zone for these stars is closer in, where planets could complete the necessary three orbits in about one Earth year.
Without the glitch, this kind of planet could in principle be confirmed in 2010. But if observations of the planet were on a noisy CCD, that confirmation would be postponed until the noise-correcting software was ready in 2011.
鈥淚t may delay the announcement of discovery by six months or a year,鈥� Borucki says.
There is some good news. The stars Kepler is staring at are less intrinsically variable than had been predicted, which should make it easier to see transiting planets. 鈥淢ost of these stars aren鈥檛 as variable as we expected and that鈥檚 going to help us,鈥� Borucki says.
