In the hunt for exoplanets (planets outside of our solar system), one of the things that astronomers have been desperately searching for is another planet like Earth that's capable of supporting life. It's been a close thing, so far. Astronomers have found Earth-sized planets in other solar systems. They have found planets in the "habitable zone" (an orbit where temperatures would be potentially conducive to life) of other solar systems. But they haven't found an Earth-sized planet in the habitable zone of another star.
Until now.
Today, NASA has announced that its Kepler telescope has uncovered a new solar system about 500 light years away, currently dubbed Kepler 186. Circling that star are five planets, and the outermost planet, Kepler-186f, is about the size of Earth and within the star's habitable zone.
"The discovery of Kepler-186f is a significant step toward finding worlds like our planet Earth," NASA's Paul Hertz said in a statement.
The star Kepler 186 is a "red dwarf" star, about half the size and mass of our own Sun. It's about 500 light years away from Earth, near the constellation Cygnus in the night sky. The planet itself orbits its sun once every 130 days.
If life does exist there, it exists in a rather darker place than Earth. It only gets about one-third of the energy from its star that the Earth gets, and at high noon it's only about as bright as the Earth is at sunset. Which might pose some interesting questions as to whether plant life could have arisen in the same way as Earth.
"Being in the habitable zone does not mean we know this planet is habitable. The temperature on the planet is strongly dependent on what kind of atmosphere the planet has," said researcher Thomas Barclay in a press release. "Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth."
But just because life doesn't exist on Kepler-186f doesn't mean we should lose hope for finding planets where there is life - the discovery itself shows that Earth-sized planets in a habitable zone aren't unique to our own solar system.
"Finding a habitable zone planet comparable to Earth in size is a major step forward," said lead researcher Elisa Quintana in a statement.
