Astronomers have found the smallest planet ever detected in the habitable zone around a star like the sun.
The new planet was found with the Kepler telescope, which searches for signs that a star鈥檚 light has dimmed because a planet has passed between it and the telescope 鈥� an event called a transit.
See graphic: Planet hunter
Advertisement
鈥淭his discovery supports the growing belief that we live in a universe crowded with life,鈥� team member Alan Boss of the Carnegie Institution for Science said in a statement. 鈥淜epler is on the verge of determining the actual abundance of habitable, Earth-like planets in our galaxy.鈥�
The planet, named Kepler-22b, lies 600 light years away around a star of the same type (called ) as the sun. It is about 2.4 times as wide as Earth and orbits its star every 290 days, right in the middle of its star鈥檚 habitable zone, where liquid water can exist on an object鈥檚 surface.
Transit observations cannot pinpoint its mass, however. Astronomers have used other telescopes to search for signs that the planet鈥檚 gravitational tugs are causing its host star to wobble, but so far have not detected any wobbles. That means the planet鈥檚 mass must be less than 36 times that of the Earth.
It is close in size to a class of planets called super-Earths, which are up to about 2 times as wide as Earth. 鈥淲e have no planet like this in our solar system,鈥� says Bill Borucki, Kepler鈥檚 chief scientist at NASA鈥檚 Ames Research Center in Moffett Field, California. He announced the find on Monday at the at NASA Ames.
Just right
The planet could be rocky and could contain water, Borucki says.
But , a graduate student at MIT, says most planets of its width are more like small gas giant planets, with a substantial gas layer surrounding a rocky core. Kepler-22b 鈥渋s probably more like a small Neptune than a scaled-up version of Earth鈥�, Rogers told New 杏吧原创.
Ground-based observations in mid-2012, when the patch of sky where the planet lies is more easily visible, could help astronomers nail down the planet鈥檚 mass. That will help them identify its composition.
Two previous rocky planet candidates have been found in the habitable zones of their stars, but in both cases the stars were cooler than the sun.
And neither candidate was found right in the middle of its star鈥檚 鈥淕oldilocks鈥� zone, which could boast the best conditions for hosting life as we know it. Kepler-22b鈥檚 surface is probably a balmy 22聽掳C, Borucki said.
Scanning for ET
The Kepler telescope has been staring at more than 150,000 stars between the constellations Cygnus and Lyra for the past 1000 days. The Kepler team has now found more than 2300 candidate exoplanets, about 1000 more than it reported in February. Ten of those span no more than about twice Earth鈥檚 width.
To confirm a new planet, scientists must observe three of its transits. Mission scientists saw the first transit of Kepler-22b three days after Kepler began collecting data in 2009. The third transit appeared in December 2010. 鈥淚t鈥檚 a great gift,鈥� Borucki said. 鈥淲e consider this our Christmas planet.鈥�
鈥淚t鈥檚 conceivable that these new planet candidates and their [potential] moons could have life,鈥� Borucki said.
The SETI Institute in Mountain View, California, will observe the new candidates with its Allen Telescope Array of radio telescopes in California in the hopes of detecting signals from any extraterrestrial civilisations there, said the institute鈥檚 . The array had been offline since April due to budget cuts but on Monday after raising funds by partnering with the US air force and .
