Search for alien life boosted by planet discoveries

Humans will probably find numerous planets like Earth in the next 10 to 20 years, greatly increasing our chances of discovering alien life, the Astronomer Royal has predicted.

Professor Sir Martin Rees will tell an audience of Britain's leading scientists this week that astronomers expect to detect Earth-like planets in our galaxy within five years. And the next big step – "photographing" those planets using the Terrestrial Planet Finder telescopes now being planned – could take only until 2010, moving us much closer to detecting planets capable of sustaining intelligent life.

"Within 20 years we may be able to hang on our walls a telescopic image of another Earth, orbiting some distant star," Sir Martin will tell a joint meeting of the Royal Society of Medicine and Royal Society for the Arts on Wednesday.

Despite this prediction, Sir Martin, of King's College Cambridge, insists he is still unsure that extraterrestrial life exists. But unlike sceptics who believe that life on Earth is a freak occurrence unlikely to be repeated, he said: "My view is that, until we know, we should be open-minded."

His remarks foreshadow an upsurge in astronomers and biologists searching for extraterrestrial life, and a growing belief that some form of very simple life could soon be discovered in our solar system. Claims five years ago that a meteorite carried Martian bacteria fossils are now widely doubted, but scientists increasingly believe that Europa, an ice-bound, water-covered moon orbiting Jupiter, could be home to basic life.

Europa's oceans should have had the raw material for life, such as carbon, nitrogen and sulphur, for millions of years from impacts by comets. NASA is building a submersible robot capable of melting ice, yet the moon is thought to have a two-mile-thick skin of ice, beyond the robot's current range.

First, however, NASA and the European Space Agency are sending probes back to Mars next year, to collect and analyse samples. Two Australian researchers will claim soon in the journal Astrobiology that the chances that life has developed on an Earth-like planet elsewhere in the universe are one in three.

Despite his public caution, Sir Martin is "enthusiastic" about attempts by the Search for Extra-Terrestrial Intelligence Institute in California to detect alien radio signals and even speculates on the form that alien life could take.

The discovery of marine species living on hot sulphur gases in the unlit depths of Earth's ocean trenches has convinced scientists that life can exist in places extremely hostile to humans. Aliens, he will say, "could be balloon-like creatures floating in dense atmospheres".