Our sun is pretty special to us, but how many other stars shine brightly enough to host a planetary party? NASA's Kepler Space Telescope has monitored more than 150,000 stars outside our solar system and 4,000 "candidate planets," according to NASA. The 1,000th exoplanet was recently identified.
Kepler data has helped scientists find a bounty of possible planets, six of which are almost the same size as Earth and orbit stars similar to our sun. Three newly validated planets could theoretically hold surface water and two of those are made of rock, like our planet.
"Each result from the planet-hunting Kepler mission's treasure trove of data takes us another step closer to answering the question of whether we are alone in the Universe," said John Grunsfeld, associate administrator of NASA's Science Mission Directorate at the Washington headquarters. "The Kepler team and its science community continue to produce impressive results with the data from this venerable explorer."
Mass is difficult to determine, but scientists can guess mass based on size. Kepler-438b and Kepler-442b, two of the newer planetary inductees are less than 1.5 times the diameter of Earth. Kepler-438b is 12 percent bigger than Earth and Kepler-442b is 33 percent bigger, according to NASA.
Kepler-438b is 475 light-years away and orbits its sun once every 35.2 days. Kepler-442b is 1,100 light-years away and a year on that planet would last 112 days.
Both exoplanets orbit stars that are cooler than our sun, so according to NASA, it is possible for them to be a closer distance to their sun but still be habitable.
"With each new discovery of these small, possibly rocky worlds, our confidence strengthens in the determination of the true frequency of planets like Earth," said co-author Doug Caldwell, SETI Institute Kepler scientist at NASA's Ames Research Center at Moffett Field, Calif. "The day is on the horizon when we'll know how common temperate, rocky planets like Earth are."
"Kepler collected data for four years -- long enough that we can now tease out the Earth-size candidates in one Earth-year orbits", said Fergal Mullally, SETI Institute Kepler scientist at Ames who is analyzing a new log of potential planets. "We're closer than we've ever been to finding Earth twins around other sun-like stars. These are the planets we're looking for."
