送交者: 2011年12月06日07:56:48 於 [世界時事論壇] 發送悄悄話

NASA finds new Earth is right for life

Bridie Smith

December 7, 2011

A PLANET capable of supporting life has been found in a distant solar system.

It has been dubbed Kepler-22b after NASA's Kepler space telescope, which first spied the planet in 2009. Scientists say its location in the habitable zone - where liquid water could exist - means conditions are right for the planet to support life.

Another feature giving astronomers hope is its relatively small size. Kepler-22b is just 2.4 times the size of the Earth, compared to Jupiter, which is 10 times larger than Earth.

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''Small planets tend to be the rocky planets,'' said Sydney University ARC postdoctoral fellow Dennis Stello, who works with Kepler. ''When looking for something that is Earth-like, we look for something that is roughly the same size, because if you have a big gas giant in the habitable zone, it's still a gas giant. You wouldn't have a surface you could walk on.''

Dr Stello works with NASA, aiding their planet hunting programs by assessing Kepler data, especially the variations in brightness of stars that have planets. These variations tell scientists about the interior of the star, which is key to understanding each planet system. Knowing the size of the star also helps estimate the size of the planet.

Dr Stello said confirmation this week that Kepler-22b was capable of supporting life was incredibly exciting.

''It's the first time that NASA has found such a small planet in the habitable zone and around a star that is very close to the sun,'' Dr Stello said. ''The system is the closest we have found yet to the system that we know.'' For now, the planet's composition remains a mystery, as scientists are yet to establish the mass of Kepler 22b. Whether the planet does support life also remains unknown.

What they do know is that Kepler 22b has its own sun-like star, which it orbits every 290 days. It is 600 light years away from its sun-like star.

Kepler 22b is the first planet in the habitable zone identified by the US space agency NASA and the third identified globally.

Earlier this year, French astronomers confirmed Gliese 581 d sat on the outskirts of the habitable zone. Just months later, HD 85512 b, one of the smallest planets outside our solar system, was discovered by Swiss astronomers in the habitable zone.

More than 700 ''exoplanets'' or planets outside our solar system have been spotted and verified in recent decades, while thousands more await confirmation by missions such as NASA's Kepler space telescope. Among these, only 15 planets and 30 moons are potentially habitable.

With GUARDIAN