NASA discovers Earth-like planet
Astronomers with NASA's Kepler mission have confirmed the existence of an Earth-like planet in a "habitable zone" around a star not unlike our own.
The planet, Kepler 22-b, lies about 600 light years away, about two-and-a-half times the size of Earth, with a temperature of about 22 degrees Celsius, allowing liquid water to exist on the surface. Its year is about 290 days long.
This is the first time the Kepler mission has detected a potentially habitable world orbiting a Sun-like star, scientists reported in findings to be published in The Astrophysical Journal.
But scientists admit they do not yet know if Kepler 22-b is made mostly of rock, gas or liquid.
"We are homing in on the true Earth-sized, habitable planets," San Jose State University astronomer Natalie Batalha said.
The planet was spotted by NASA's Kepler Space Telescope, which was launched three years ago.
The telescope 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.
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," Dr Batalha said.
Among the 2326 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," astronomer Jill Tarter, director of the SETI Institute, said.
The Kepler team is meeting for its first science conference this week.