Distant Earth-Sized Planet Has Right Conditions for Water, Perhaps Life

Using the Kepler Space Telescope, astronomers made a landmark discovery: the first Earth-sized planet within the habitable zone of a star, where water could exist in liquid form.

Although vital data such as the planet's mass, whether it has an atmosphere and whether it actually has water are still unclear, astronomers report that the planet - for now named Kepler-186f - is the most Earth-like planet ever found.

The team of astronomers behind the discovery have published their work in the journal Science.

"We know of just one planet where life exists - Earth. When we search for life outside our solar system we focus on finding planets with characteristics that mimic that of Earth," lead study author Elisa Quintana, research scientist at the SETI Institute at NASA's Ames Research Center in Moffett Field, Calif., said in a statement. "Finding a habitable zone planet comparable to Earth in size is a major step forward."

Other Earth-sized planets have been found before, but they have all been either too close or too far away from their stars to make them candidates for supporting life as we know it.

Three years of observational radiation data taken from Kepler-186f suggest that the planet could have an Earth-like atmosphere and perhaps liquid water at its surface.

"The host star, Kepler 186, is an M1-type dwarf star which means it will burn hydrogen forever, so there is ample opportunity to develop life around this particular star and because it has just the right orbital period water may exist in a liquid phase on this planet," Notre Dame astrophysicist  and study co-author Justin R. Crepp said in a statement. 

Geoffrey Marcy, an astronomer at the University of California, Los Angeles, not involved in the study told the LA Times that the discovery was "historic."

"This is the best case for a habitable planet yet found," he said. "The results are absolutely rock solid."

The planet, while it may look like home, is not anywhere near it. Kepler-186f is about 490 light-years away in the constellation Cygnus. Its M-class star is smaller than our Sun, so even though its orbit is closer to the star - it takes just 130 days for the planet to circle it - the star is cool enough that the planet is still in the habitable zone.

Moreover, the planet sits on the outer edge of the star's habitable zone, which will likely protect it from the flares and radiation M-class stars are known to emit. The plant is in a solar system with at least four other companions, all of which are too hot to be in the habitable zone of their star.

However, more data will need to be established before any concrete determination about life on Kepler-186f can be made.

"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 research co-author Thomas Barclay, a research scientist at the Bay Area Environmental Research Institute at Ames. "Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth."

Dimitar Sasselov, a planetary astrophysicist at the Harvard-Smithsonian Center for Astrophysics who was not involved in the paper, told the LA Times he was optimistic about the discovery.

"Whether we are an extremely rare fluke - a phenomenon that only happens once in a universe - or in a galaxy teeming with life is a very basic question not only of science, but of our existence," he said. It's "the first time in human history we have a good shot at answering that question, and that's very exciting."