New planets discovered 2014

For the first time, scientists have discovered an Earth-size alien planet in the habitable zone of its host star, an "Earth cousin" that just might have liquid water and the right conditions for life.

This artist illustration shows what it might be like to stand on the surface of the planet Kepler-186f, the first-ever Earth-size planet to be found in the habitable zone of its star.

The newfound planet, called Kepler-186f, was first spotted by NASA's Kepler space telescope and circles a dim red dwarf star about 490 light-years from Earth. While the host star is dimmer than Earth's sun and the planet is slightly bigger than Earth, the positioning of the alien world coupled with its size suggests that Kepler-186f could have water on its surface, scientists say. You can learn more about the amazing alien planet find in a video produced by Space.com.

"One of the things we've been looking for is maybe an Earth twin, which is an Earth-size planet in the habitable zone of a sunlike star, " Tom Barclay, Kepler scientist and co-author of the new exoplanet research, told Space.com. "This [Kepler-186f] is an Earth-size planet in the habitable zone of a cooler star. So, while it's not an Earth twin, it is perhaps an Earth cousin. It has similar characteristics, but a different parent." [10 Exoplanets That Could Host Alien Life]

This artist illustration shows the planet Kepler-186f, the first Earth-size alien planet discovered in the habitable zone of its star.

Potentially habitable planet

Scientists think that Kepler-186f — the outermost of five planets found to be orbiting the star Kepler-186 — orbits at a distance of 32.5 million miles (52.4 million kilometers), theoretically within the habitable zone for a red dwarf.

Earth orbits the sun from an average distance of about 93 million miles (150 million km), but the sun is larger and brighter than the Kepler-186 star, meaning that the sun's habitable zone begins farther out from the star by comparison to Kepler-186.

"This is the first definitive Earth-sized planet found in the habitable zone around another star, " Elisa Quintana, of the SETI Institute and NASA's Ames Research Center and the lead author of a new study detailing the findings, said in a statement.

Other planets of various sizes have been found in the habitable zones of their stars. However, Kepler-186f is the first alien planet this close to Earth in size found orbiting in that potentially life-supporting area of an extrasolar system, according to exoplanet scientists.

'An historic discovery'

"This is an historic discovery of the first truly Earth-size planet found in the habitable zone around its star, " Geoff Marcy, an astronomer at the University of California, Berkeley, who is unaffiliated with the research, told Space.com via email. "This is the best case for a habitable planet yet found. The results are absolutely rock-solid. The planet itself may not be, but I'd bet my house on it. In any case, it's a gem."

The newly discovered planet measures about 1.1 Earth radii, making it slightly larger than Earth, but researchers still think the alien world may be rocky like Earth. Researchers still aren't sure what Kepler-186f's atmosphere is made of, a key element that could help scientists understand if the planet is hospitable to life. [Kepler-186f: Earth-Size World Could Support Oceans, Maybe Life (Infographic)]

"What we've learned, just over the past few years, is that there is a definite transition which occurs around about 1.5 Earth radii, " Quintana said in a statement. "What happens there is that for radii between 1.5 and 2 Earth radii, the planet becomes massive enough that it starts to accumulate a very thick hydrogen and helium atmosphere, so it starts to resemble the gas giants of our solar system rather than anything else that we see as terrestrial."

This diagram shows the position of Kepler-186f in relation to Earth.