It 's like finding a needle in a universe-wide haystack . Researchers have located a planet roughly the size of Earth that could be habitable . Designated Kepler-186f , the planet is 490 light-years away . But in the search for worlds similar to ours , nothing has come closer . `` This is the first definitive Earth-sized planet found in the habitable zone around another star , '' said Elisa Quintana of the Search for Extraterrestrial Intelligence ( SETI ) Institute at NASA . `` Finding such planets is a primary goal of the Kepler space telescope . '' `` This discovery not only proves the existence of worlds that might be similar to our own but will undoubtedly shape future investigations of exoplanets that could have terrestrial surface environments , '' the institute said in an announcement Thursday . After spotting it , the institute wasted no time searching for emissions that could indicate the presence of ETs . So far , no emissions have been found . The size -- estimated to be 10 % larger than Earth -- and distance from its star do n't just make for interesting factoids . They give scientists hope that Kepler-186f might sustain life as we know it . Of nearly 1,800 `` confirmed exoplanets '' that have been found , approximately 20 orbit their host stars within habitable zones , where it 's believed surface water would not freeze or boil . In 2011 , NASA announced that Kepler had observed five planets approximately the size of Earth and in the habitable zone . But the `` previously discovered worlds are larger than Earth , and consequently their true nature -- rocky or gaseous -- is unknown , '' the SETI Institute said in a written announcement on Thursday . `` On the basis of the observed dimming of starlight from Kepler-186 , the authors estimate that this newly discovered planet is roughly the same size as the Earth . '' Theoretical models and observations tell scientists that planets the size of Kepler-186f likely have a composition of iron , rock and ice , like Earth , Quintana told reporters Thursday . Even if Kepler-186f is rocky , it 's not necessarily habitable , scientists warned Thursday . First , a lot would depend on the atmosphere , if it has one , Thomas Barclay of NASA 's Kepler mission said . And scientists right now do n't have the technology to know what the atmosphere is . The star 's size -- it 's an M-dwarf star , smaller and less hot than our sun -- also could come into play . Because it is smaller , the habitable zone is closer , so radiation could prevent life if the atmosphere is n't dense enough , said Victoria Meadows of the University of Washington Virtual Planetary Laboratory . But the Webb space-based telescope , now under construction , should be able to gather images of planets around closer dwarf stars and study their atmospheres . Scientists are especially keen about checking dwarf stars because their habitable planets are more easily detectable , and because they are the most abundant type of star in our galaxy , Barclay said . For researchers , the discovery of Kepler-186f is like a beginning . It 's a first but `` not a record we wish to keep , '' Quintana said . `` We want to find more of these . '' It 's likely they will . Astronomers at the University of California , Berkeley , and the University of Hawaii , using data from Kepler , estimate there are tens of billions of Earth-size , possibly habitable planets in our Milky Way galaxy .
They discovered an Earth - sized planet that might be habitable . It ` ` ##s the existence of worlds that might be similar to our own , '' institute says . Scientists are looking for emissions that could indicate extraterrestrial life . Previously , worlds were larger than Earth .