Previous research had hinted at the existence of such Earth-like planets, where liquid water could exist, but this is the first time such a life-friendly alien planet has been confirmed.
The planet, known as Kepler-22b, is among 29 confirmed and 2,326 candidate worlds found by a team of astronomers using NASA's Kepler Space Telescope.
Kepler-22b is the smallest planet yet to be found beyond our solar system in the region most conducive to life as we know it on Earth.
"If the greenhouse warming was similar on this planet and if it had a surface, its temperature would be something like 72 degrees Fahrenheit, a very pleasant temperature here on the Earth," William Borucki, lead Kepler researcher at NASA's Ames Research Center in Moffett Field, Calif., said at a press briefing Monday.
The planet is around 2.4 times wider than Earth -- making it a "super-Earth." It takes 289.9 days to fly around its parent star, which is very much like our sun.
"It's almost a solar twin," Batalha said.
More work is needed before scientists will be able to tell if Kepler-22b is rocky like Earth, gaseous like Neptune, or more probably, a mix. But its discovery is a milestone on the road to finding bona fide Earth-like planets.
"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," said Natalie Batalha, Kepler deputy science team lead at San Jose State University.
The Kepler team's targets also will be scrutinized by the independent SETI Institute, which surveys stars in the Milky Way for non-naturally occurring radio signals, a project known as the Search for Extraterrestrial Intelligence, or SETI.
"There are so many special things about Earth," SETI Institute director Jill Tarter told Discovery News. "We have an example of one. In a physics experiment, when when there are multiple outcomes you want to run that experiment many times. We haven't been able to do those experiments yet. We don't know whether the Earth as it is and life as we know it here -- the way we got here was very unusual, that elsewhere things go in a different way. Or are we common?
"This is a work in progress," she said. "In this field, number two is the all-important number because 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."
So far, Kepler-22b seems to be flying solo, with no sibling planets, but that conclusion may change. Smaller worlds like Earth require more time for the Kepler team to make observations.
The telescope is staring at about 150,000 stars in the constellations Cygnus and Lyra looking for the miniscule dimming of light that happens when a planet or planets pass across or "transit" -- the stars.
In addition to confirming Kepler-22b, the telescope team discovered more than 1,000 new planet candidates. The recent haul nearly doubles its previously known count. Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host stars.
Read more at Discovery News
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