For the first time, scientists have found an Earth-sized world orbiting in a life-friendly zone which may actually be a true Earth cousin. Unfortunately, this star about which it rotates, known as Kepler-186, is located about 500 light years away in the constellation Cygnus.
"It's like a camp fire. You could get burned or you could be too chilly. This is the optimal distance," Jason Rowe, research scientist with the SETI Institute and member of the Kepler Science Team at NASA, told the Daily News. "If you start finding them around stars that are 50 light years away," Rowe said, "we could check to see if they have an appreciable atmosphere that could be amenable to life."
Kepler-186f, the star’s outermost planet, receives about one-third the radiation from Kepler-185 as Earth gets from the sun, meaning high noon on this newly discovered world would be roughly akin to our world an hour before sunset, according to astronomer Thomas Barclay with NASA’s Ames Research Center in Moffett Field, California. The planet is also the right distance from its host star for water – should any exist – to be liquid on the surface, a condition scientists suspect is necessary for life.
"This planet is an Earth cousin, not an Earth twin," said Barclay, who is among a team of scientists reporting on the discovery in the journal Science this week.
NASA launched its Kepler space telescope in 2009 to search about 150,000 target stars for signs of any planets passing by, or transiting, relative to the telescope's point of view. Kepler was sidelined by a positioning system failure last year. Analysis of archived Kepler data continues, however it is a very time-consuming process.
"It's very challenging to find Earth analogs," Barclay said. "Most candidates don't pan out, but things change as we get more measurements."
Scientists don't know anything about the atmosphere of Kepler-186f, but it will be a target for future telescopes that can scan for telltale chemicals that may be linked to life.
"This planet is in the habitable zone, but that's doesn't mean it is habitable," Barclay said.
Scientists have found nearly 1,800 planets beyond the solar system during this process.
"The past year has seen a lot of progress in the search for Earth-like planets. Kepler-168f is significant because it is the first exoplanet that is the same temperature and is (almost) the same size as Earth," astronomer David Charbonneau, with the Harvard-Smithsonian Center for Astrophysics, wrote in an email. "For me the impact is to prove that yes, such planets really do exist," Charbonneau said. "Now we can point to a star and say, "There lies an Earth-like planet.'"
“This is the best case for a habitable planet yet found. The results are absolutely rock solid,” University of California, Berkeley astronomer Geoff Marcy, who had no role in the discovery, said in an email.