(CNN) -- It's like finding a needle in a universe-wide haystack. Researchers have located a planet 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, none found.
The size doesn't just make for an interesting factoid. It gives 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 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."
The planet is also far enough away from its star to avoid dangers to potential life, including from stellar flares given off by dwarf stars.
In anticipation of NASA's announcement Thursday, DailyGalaxy.com asked whether Kepler-186f may prove to be a "twin Earth."
"Kepler-186f is likely a rocky world and in that sense similar to Venus, Earth and Mars," said Thomas Barclay of NASA's Kepler mission.
Even the best technology isn't strong enough to tell scientists about the planet's atmosphere at this point. 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.
For researchers, the discovery of Kepler-186f is like a new 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.
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