Two Promising Places to Live, 1,200 Light-Years From Earth

American Association for the Advancement of Science

An artist's impression of a sunrise on Kepler 62f. The two outer planets of the Kepler 62 system may lie in the habitable zone, where liquid water could exist on the surface.

Astronomers said Thursday that they had found the most Earth-like worlds yet known in the outer cosmos, a pair of planets that appear capable of supporting life and that orbit a star 1,200 light-years from here, in the northern constellation Lyra.

They are the two outermost of five worlds circling a yellowish star slightly smaller and dimmer than our Sun, heretofore anonymous and now destined to be known in the cosmic history books as Kepler 62, after NASA’s Kepler spacecraft, which discovered them. These planets are roughly half again as large as Earth and are presumably balls of rock, perhaps covered by oceans with humid, cloudy skies, although that is at best a highly educated guess.

Nobody will probably ever know if anything lives on these planets, and the odds are that humans will travel there only in their faster-than-light dreams, but the news has sent astronomers into heavenly raptures. William Borucki of NASA’s Ames Research Center, head of the Kepler project, described one of the new worlds as the best site for Life Out There yet found in Kepler’s four-years-and-counting search for other Earths. He treated his team to pizza and beer on his own dime to celebrate the find (this being the age of sequestration). “It’s a big deal,” he said.

Looming brightly in each other’s skies, the two planets circle their star at distances of 37 million and 65 million miles, about as far apart as Mercury and Venus in our solar system. Most significantly, their orbits place them both in the “Goldilocks” zone of lukewarm temperatures suitable for liquid water, the crucial ingredient for Life as We Know It.

Goldilocks would be so jealous.

 

Previous claims of Goldilocks planets with “just so” orbits snuggled up to red dwarf stars much dimmer and cooler than the Sun have had uncertainties in the size and mass and even the existence of these worlds, said David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, an exoplanet hunter and member of the Kepler team.

“This is the first planet that ticks both boxes,” Dr. Charbonneau said, speaking of the outermost planet, Kepler 62f. “It’s the right size and the right temperature.” Kepler 62f is 40 percent bigger than Earth and smack in the middle of the habitable zone, with a 267-day year. In an interview, Mr. Borucki called it the best planet Kepler has found.

Its mate, known as Kepler 62e, is slightly larger — 60 percent bigger than Earth — and has a 122-day orbit, placing it on the inner edge of the Goldilocks zone. It is warmer but also probably habitable, astronomers said.

The Kepler 62 system resembles our own solar system, which also has two planets in the habitable zone: Earth — and Mars, which once had water and would still be habitable today if it were more massive and had been able to hang onto its primordial atmosphere.

The Kepler 62 planets continue a string of breakthroughs in the last two decades in which astronomers have gone from detecting the first known planets belonging to other stars, or exoplanets, broiling globs of gas bigger than Jupiter, to being able to discern smaller and smaller more moderate orbs — iceballs like Neptune and, now, bodies only a few times the mass of Earth, known technically as super-Earths. Size matters in planetary affairs because we can’t live under the crushing pressure of gas clouds on a world like Jupiter. Life as We Know It requires solid ground and liquid water — a gentle terrestrial environment, in other words.

Kepler 62’s newfound worlds are not quite small enough to be considered strict replicas of Earth, but the results have strengthened the already strong conviction among astronomers that the galaxy is littered with billions of Earth-size planets, perhaps as many as one per star, and that astronomers will soon find Earth 2.0, as they call it — our lost twin bathing in the rays of an alien sun.

“Kepler and other experiments are finding planets that remind us more and more of home,” said Geoffrey Marcy, a longtime exoplanet hunter at the University of California, Berkeley, and Kepler team member. “It’s an amazing moment in science. We haven’t found Earth 2.0 yet, but we can taste it, smell it, right there on our technological fingertips.”

A team of 60 authors, led by Mr. Borucki, reported the discovery of the Kepler 62 planets on Thursday in an article published online in the journal Science and at a news conference at Ames.

As if that weren’t enough, a group led by Thomas Barclay of Ames and the Bay Area Environmental Research Institute also reported the discovery of a planet 1.7 times as big as Earth hovering on the inner, warmer edge of the Goldilocks zone of Kepler 69, a star almost identical to the Sun, 2,700 light-years distant. At the news conference, Dr. Barclay described the planet as perhaps a “Super-Venus.” The group’s paper was published on Thursday in The Astrophysical Journal.