Astronomers may be on the brink of discovering a second Earth-like planet, a find that will add fresh impetus to the search for extra-terrestrial life, a leading science journal has claimed.

Planet hunters have spotted more than 200 planets beyond the solar system, but the vast majority are hot, Jupiter-sized planets that will dwarf Earth and are almost certainly lifeless.

Writing in the US journal Science, astronomers from six major centres, including NASA, Harvard and the University of Colorado, outline how advances in technology suggest scientists are on the verge of being able to detect the presence of small, rocky planets, much like our own, around distant stars for the first time.

The planets are considered the most likely havens for extra-terrestrial life. One technique relies on observing the shift in light, coming from a star as a planet swings around it. Until recently, this radial velocity method has only been sensitive enough to pick up planets far more massive than Earth, but improvements now make the discovery of a second Earth highly likely, said Dave Latham, a co-author on the paper at the Harvard-Smithsonian Centre for Astrophysics.

"It could happen almost anytime now. We have the technological capability to identify Earth-like planets around the smallest stars even now," he told the journal. Dr Latham said missions such as NASA's planned Kepler space observatory, which is due to launch in early 2009, would have a high chance of finding Earth-like planets if they are out there.

"These are the biggest questions. Are these habitable abodes? Are we alone?" he said. "Put it like this. If we don't find anything, I'll have to rethink my agnosticism."