Telescopes on Mauna Kea have confirmed the discovery of Earth’s first twin, a planet about the same size that could harbor water.
The bad news is it’s too far away for humans to ever get to unless someone invents some kind of "Star Trek" warp drive.
The planet is around a star called Kepler-186, about 500 light-years away in the constellation Cygnus the Swan.
The planet, Kepler-186f, lies in the so-called "Goldilocks Zone" — that is, in an orbit that is just the right distance from the star so the planet is neither too hot nor too cold, scientists announced Thursday.
"This is the best case for a habitable planet yet found," said Geoff Marcy, an astronomer at the University of California at Berkeley who was not involved in the research.
"The results are absolutely rock solid," Marcy said by email. "The planet itself may not be, but I’d bet my house on it. In any case, it’s a gem."
Elisa Quintana of the NASA Ames Research Center was the lead author of the study, appearing in the current issue of the journal Science.
"What makes this finding particularly compelling is that this Earth-sized planet — one of five orbiting this star, which is cooler than the sun — resides in a temperate region where water could exist in liquid form," Quintana said in a statement.
The discovery, made initially by NASA’s orbiting Kepler Space Telescope, was confirmed by observations from the Keck Observatory and Gemini Observatory on Mauna Kea.
"The Keck and Gemini data are two key pieces of this puzzle," Quintana said. "Without these complementary observations, we wouldn’t have been able to confirm this Earth-sized planet."
The host star is a red dwarf and very dim.
Five small planets have been found around it, four of which are in very short-period orbits and are very hot. Kepler-186f, however, is Earth-sized and within the star’s habitable zone.
Artist renderings of this world show water and vegetation.
Astronomers generally agree these days that plenty of habitable Earth-sized planets exist around other stars. In fact, 1 in 5 sunlike stars has one, according to a statistical study last fall by the University of Hawaii and UC-Berkeley.
The challenge has been to find them, and Kepler-186f is the first.
The Kepler observatory, launched in March 2009, looks at stars in a small patch of the sky near the constellation Cygnus. It has a photometer that measures the brightness of stars, watching for a telltale, minute dip in brightness when a planet passes in front of it.
In the years since its launch, Kepler has identified more than 2,700 "candidate" planets in that small section of the galaxy.
Then it falls to the sophisticated instruments at Keck Observatory to confirm that the so-called "transit" was caused by a planet.
In the case of Kepler-186f, observations from both Keck and its neighbor, Gemini, were required for the confirmation.
That’s because no telescope is currently able to spot an exoplanet of that size and proximity to its star, said Steve Howell, Kepler’s project scientist and a co-author on the paper.
"However, what we can do is eliminate essentially all other possibilities so that the validity of these planets is really the only viable option," Howell said in a statement.
Thomas Barclay, a Kepler scientist and another co-author on the paper, said the research team is "99.98 percent confident that Kepler-186f is real."
Marcy said the planet’s size is easily measured from Kepler data to be only 11 percent larger than Earth.
Within the margin of error, "it may be the same size as Earth," he said.
He added, "The host star dims every time the planet crosses in front, like clockwork, telling us the time for the planet to complete one orbit. The brilliant conclusion is that the planet is quite likely to be rocky, like Earth, based on other planets in its size range. This planet is modestly illuminated by its host star, a red dwarf. This planet basks in an orange-red glow from that star, much like we enjoy at sunset."
Essential to the discovery was the Keck II’s "adaptive optics," which eliminates much of the distortion caused by the atmosphere. At an elevation of nearly 13,800 feet, Mauna Kea is already above much of the thickest layers of the atmosphere, making it one of the premier astronomical sites in the world.
On Gemini North, the Differential Speckle Survey Instrument took multiple short exposures of the object to remove the effects of atmospheric turbulence, Howell said.
"We can probe down into this star system to a distance of about four times that between the Earth and the sun," he said. "It’s simply remarkable that we can look inside other solar systems."
Last October, astronomers using Kepler and Keck announced the discovery of the first extrasolar planet, or exoplanet, that is the same size as Earth and has a rocky composition like Earth’s. But Kepler-78b is much too hot for life.
Quintana is also with the SETI Institute, a Mountain View, Calif.-based group founded by Carl Sagan, involved in the search for extraterrestrial intelligence.
Of course, there is no evidence at this point that Kepler-186f has life, intelligent or otherwise.
But someday, scientists say, it may be possible to remotely sense so-called "biomarkers" — clues that life exists — around exoplanets, especially if they are close.
"These Earth-sized planets are extremely hard to detect and confirm, and now that we’ve found one, we want to search for more," Quintana said. "Gemini and Keck will no doubt play a large role in these endeavors."
