A planet similar to Earth could be discovered in a distant solar system within three years, according to a leading astronomer.
Planets that support life forms could be common in the universe, and about 100bn of them may exist in our own galaxy, said Dr Alan Boss, a researcher at the Carnegie Institute for Science in Washington.
He told a meeting of the American Association for the Advancement of Science in Chicago yesterday that, according to his calculations, there is roughly one Earth-like planet for every star that is similar to our own sun.
The US space agency, Nasa, is due to launch a space telescope, called Kepler, dedicated to searching for planets that are similar to, or smaller than Earth. It will join the European Space Agency's Corot telescope, which spotted a large "super Earth" earlier this month.
The Kepler telescope will gaze continuously at 100,000 stars in two constellations known as Cygnus and Lyra for more than three years.
"Within three to four years from now, these telescopes will tell us just how frequently Earths occur. It's an exciting time to be alive," Boss said.
"We will be absolutely astonished if Kepler and Corot don't find any Earth-like planets. If there's nothing lying in that region of space that corresponds to Earth, it would be a reason for mass harakiri in parts of the community," he added.
The hunt for planets beyond our own cosmic neighbourhood solar system has already revealed more than 300 distant worlds, though the majority of these are unlikely to be hospitable.
About a third of nearby suns have planets that are five or 10 times the size of Earth, but they orbit their stars more closely and hence are much hotter.
The number of planets like Earth, which are orbiting in the "Goldilocks" region of space where the temperature is right for liquid water, could be much higher, an estimated 10,000bn billion in the observable universe, said Boss.
"If we find that Earth-like planets are as common as I'm claiming, we'll make a very strong case that not only are they probably habitable, they are also going to be inhabited, but that will be up to the next generation of space telescopes to prove," Boss said.
"Most likely, the nearby Earths are going to be inhabited with organisms which are more common to things that were found on Earth three or four billion years ago, so simple, single-celled creatures. What I suspect we'll find first is a nearby Earth-like world has some sort of methane-producing bacteria sliming its surface up. Just the fact that we can find evidence for life beyond Earth will answer the question: Are we alone? And we're going to find out the answer is 'No we are not'."
Astronomers have pondered over the existence of planets beyond our solar system since before the days of Sir Isaac Newton, but it was not until 1988 that a planet was detected orbiting a star called Gamma Cephei, 45 light years away, by Canadian researchers.
Almost all the planets discovered outside our own solar system have been spotted as they pass in front of the face of their parent star, or by the gravitational forces they exert on the star as they orbit it.
