A NASA team has found a small planet best positioned to have liquid water but has yet to determine whether it is solid.

Scientsts confirm Kepler-22b and is about 2.4 times the radius of earth and orbits a star similar to the earth’s sun [AFP]

The most Earth-like planet ever discovered is circling a star 600 light years away, a key finding in an ongoing quest to learn if life exists beyond Earth, scientists have said.

The planet, called Kepler-22b, joins a list of more than 500 planets found to orbit stars beyond our solar system. It is the smallest and the best positioned to have liquid water on its surface — among the ingredients necessary for life on Earth.

“We are homing in on the true Earth-sized, habitable planets,” said San Jose State University astronomer Natalie Batalha on Monday.

Batalha is the deputy science team leader for NASA’s Kepler Space Telescope, which discovered the star.

The telescope, which was launched three years ago, is staring at about 150,000 stars in the constellations Cygnus and

Lyra, looking for faint and periodic dimming as any circling planets pass by, relative to Kepler’s line of sight.

Results will be extrapolated to determine the percentage of stars in the Milky Way galaxy that harbour potentially habitable, Earth-size planets.

This is the first detection of a potentially habitable world orbiting a Sun-like star, scientists reported in findings to be published in The Astrophysical Journal.

Kepler-22b is 600 light years or roughly 6 trillion miles away.

Ground telescopes

Planets about the same distance from their parent stars as Earth take roughly a year to complete an orbit. Scientists want to see at least three transits to be able to rule out other explanations for fluctuations in a star’s light, such as small

companion stars.

Results also are verified by ground and other space telescopes.

Kepler-22b, which is about 2.4 times the radius of Earth, sits squarely in its star’s so-called “habitable zone,” the

region where liquid water could exist on the surface. Follow-up studies are under way to determine if the planet is solid, like Earth, or more gaseous like Neptune.

“We don’t know anything about the planets between Earth-size and Neptune-size because in our solar system we have

no examples of such planets.

“We don’t know what fraction are going to be rocky, what fraction are going to be water worlds, what fraction are ice worlds.

“We have no idea until we measure one and see,” Batalha said at a news conference at NASA Ames Research Center in Moffet Field, California.

If Kepler-22b has a surface and a cushion of atmosphere similar to Earth’s, it would be about 22 degrees Celsius, about the same as a spring day in Earth’s temperate zone. Among the 2,326 candidate planets found by the Kepler team, 10 are roughly Earth-size and reside in their host stars’ habitable zones.

Another team of privately funded astronomers is scanning the target stars for non-naturally occurring radio signals,

part of a project known as SETI, or the Search for Extraterrestrial Intelligence.

“As soon as we find a different, a separate, an independent example of life somewhere else, we’re going to know that it’s

ubiquitous throughout the universe,” said astronomer Jill Tarter, director of the SETI Institute in Mountain View.

The Kepler team is meeting for its first science conference this week.