NASA has found a new planet outside Earth's solar system that is eerily similar to Earth in important aspects.
Scientists say the temperature on the surface of the planet, known as Kepler-22b, is about a comfy 72 degrees (22 Celsius). Its star could almost be a twin of Earth's sun. It probably has water and land.
It was found in the middle of the habitable zone, making it the best potential target for life. However, getting there would take some time: Kepler-22b is about 600 light years away (A light year is the distance light travels in a year, or about 6 trillion miles.)
The discovery announced Monday was made by NASA's Kepler planet-hunting telescope. This is the first time the agency has confirmed a planet outside Earth's solar system in the not-too-hot, not-too-cold habitable zone. This is the region around a star where liquid water, a requirement for life on Earth, could persist. The planet is estimated to be 2.4 times the size of Earth, which would make it the smallest found to orbit in the middle of the habitable zone of a star like our sun.
Twice before astronomers have announced planets found in that zone, but neither was as promising. One was disputed; the other is on the hot edge of the zone. Kepler 22-B is the smallest and the best positioned of the more than 500 planets found to orbit stars beyond our solar system to have liquid water on its surface -- among the ingredients necessary for life on Earth.
With the discovery, the Kepler space telescope has now located 2,326 potential planets during its first 16 months of operation.
"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."
For the scientists working on the project, the confirmation of a near-Earth-size planet was the culmination of a difficult search marked by fits and starts. Although earlier research had hinted at the existence of near-Earth-size planets in the so-called habitable zones, they said that getting clear confirmation proved elusive. In February, 54 habitable zone planet candidates were first reported but Kepler-22b is the first to be confirmed.
"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.. He directed 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."