NASA scientists said the Kepler mission had confirmed finding
three planets, slightly larger than Earth, orbiting in their
stars' so-called habitable zones - the ''Goldilocks'' region
where temperatures are not too hot and not too cold.
Researchers don't know for sure but the planets' sizes and
proximity to their stars mean that they could be rocky and could
have liquid water - two attributes thought necessary for a
planet to harbour life.  What is certain, the scientists said
during a news conference on Thursday, is that the discoveries
mark yet another step forward in the space agency's quest to
find an Earth-size planet in a star's habitable zone.  ''We're
not quite there but we're pushing towards it,'' said Thomas
Barclay, a Kepler scientist at the Bay Area Environmental
Research Institute in California.  ''These are our best
candidates for planets that might be habitable,'' said William
Borucki, Kepler science principal investigator at NASA's Ames
Research Centre in Moffett Field, California, and a long