NASA readies search for other Earths with Kepler launch

Washington  - Are we alone in the universe? Are there other planets like Earth? Scientists will attempt to answer those questions with a telescope being launched into orbit on Friday.

The Kepler spacecraft is to launch at 10:49 pm (0349 GMT Saturday) aboard a Delta II rocket from Cape Canaveral, Florida.

Scientists are quick to point out that the programme could have major historic implications, providing knowledge of just how common - or rare - Earth is.

It "could tell us that we have lots of neighbours or that we are perhaps the only one," said researcher Ed Weiler.

The 590-million-dollar telescope programme will spend at least the next three and a half years pointed at a large swath of the Milky Way Galaxy containing some 4.5 million stars.

The most advanced cameras ever used in space will focus on some 100,000 to 150,000 stars deemed most likely to have planets orbiting them, scientists said at a pre-launch press briefing. Data from the cameras will be used to find planets by looking for blips in the amount of light being emitted as a planet crosses in front of the star.

An Earth-sized planet will be particularly hard to spot because of its size and the fact that it will cross in front of its sun only once a year, scientists said.

Since 1995, more than 340 planets have been found outside our solar system, but these so-called exoplanets have been large, gaseous planets, like Jupiter, which tend to be closer to their stars and easier to spot because of their size. Planets like Earth, which could be capable of housing life, can exist only in a small "habitable zone" within a certain distance from their sun.

The known exoplanets are "nothing at all like our solar system, which we know so well and we have yet to discover a true analog to Earth," said Padi Boyd, a scientist for the programme who called Kepler "essentially a planet sifter for Earths."

Still, Kepler, named for the German scientist Johannes Kepler, will scan just a small portion of the sky - about as much as would be covered by the hand of a human standing on Earth with an arm outstretched.

And if it finds an Earth-sized planet, scientists will still have a lot of work to do to determine whether conditions there would be hospitable to life because many other conditions, such as the existence of water and temperature, would also have to be right.

The mission will provide "an assessment of the real estate market of other rocky planets, but it won't actually tell us how nice the homes are," said scientist Gibor Basri, noting that will have to wait for other missions. (dpa)