NASA has confirmed the existence of an earth-like planet circling a star, 600 light years away from us.

Planet found orbiting habitable zone of sun-like star

 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 said on Monday.

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.

The planet contains both land and water and has a "similar temperature to that of the Earth" of around 72 degrees (22 Celsius).

It is 2.4 times the size of Earth and has a slightly shorter orbit than our planet, of 290 days.

There are now three planets outside the system, known as exoplanets, which experts believe could potentially be colonised by future generations.

In May, French astronomers identified Gliese 581d, pronounced “gleezer”, which is far closer at around 20 light years away.

It is about six times the mass of Earth and is one of a family of at least six planets.

In August, a team from Switzerland reported that another planet 36 light years away called HD 85512b seemed to be habitable.

The planet is in the constellation of Vela, and measures around 3.6 times the Earth's mass.

"We are homing in on the true Earth-sized, habitable planets," said San Jose State University astronomer Natalie Batalha, deputy science team lead for NASA's Kepler Space Telescope that 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 harbor 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 away. A light year is the distance light travels in a year, about 6 trillion miles (10 trillion km).


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 72 degrees Fahrenheit (22 C), 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.

 The Kepler Science Conference is happening Dec 5 through 9.
Watch it online at: http://connect.arc.nasa.gov/kepler

This image is an artist's conception of planet Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. It is the first planet that NASA's Kepler mission has confirmed to orbit in a star's habitable zone -- the region around a star where liquid water, a requirement for life on Earth, could persist. The planet is 2.4 times the size of Earth, making it the smallest yet found to orbit in the middle of the habitable zone of a star like our sun.

Scientists do not yet know if the planet has a predominantly rocky, gaseous, or liquid composition. It's possible that the world would have clouds in its atmosphere, as depicted here in the artist's interpretation.
Kepler also has discovered more than 1,000 new planet candidates, nearly doubling its previously known count. Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host star. Since the last catalog was released in February, the number of planet candidates identified by Kepler has increased by 89 percent and now totals 2,326. Of these, 207 are approximately Earth-size, 680 are super Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. The number of Earth-size and super Earth-size candidates has increased by more than 200 and 140 percent since February, respectively. There are 48 planet candidates in their star's habitable zone, a decrease from the 54 reported in February, because the Kepler team has applied a stricter definition of what constitutes a habitable zone in the new catalog, to account for the warming effect of atmospheres, which would move the zone away from the star, out to longer orbital periods.

Quotes from Kepler team:

"This is a major milestone on the road to finding Earth's twin," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Kepler's results continue to demonstrate the importance of NASA's science missions, which aim to answer some of the biggest questions about our place in the universe."


"Fortune smiled upon us with the detection of this planet," said William Borucki, Kepler principal investigator at NASA Ames Research Center at Moffett Field, Calif., who led the team that discovered Kepler-22b. "The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season."

"The tremendous growth in the number of Earth-size candidates tells us that we're honing in on the planets Kepler was designed to detect: those that are not only Earth-size, but also are potentially habitable," said Natalie Batalha, Kepler deputy science team lead at San Jose State University in California. "The more data we collect, the keener our eye for finding the smallest planets out at longer orbital periods."

This diagram below compares our own solar system to Kepler-22. The diagram includes the habitable zone where water can exist in liquid form. Kepler-22's star is a bit smaller than our sun, so it's habitable zone is slightly closer in. The orbit of Kepler-22b around its star takes 289 days and is about 85% as large as Earth's orbit.