Two Earth-Sized Planets with Earth-Like Temperatures Discovered by Kepler

BY Jenny Marder  April 18, 2013 at 5:15 PM EDT

The artist’s concept depicts Kepler-62e, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra. Photo by NASA Ames/JPL-Caltech.

Two Earth-sized planets with lukewarm temperatures have been discovered by NASA’s Kepler space telescope. They are 1,200 light years away, orbiting a star in the constellation Lyra, and their distance from their host star means that they exist in the zone that could potentially host life. And their temperatures are not unlike an early Spring day on Earth.

“Aristotle himself asked whether our planet Earth is unique and whether there might be other Earths,” said Geoff Marcy, a professor of astronomy at the University of California at Berkeley. “And scientists and philosophers have been asking for 2,000 years since whether our Earth has a twin.”

“It’s exciting,” he continued, “to see planets emerging from Kepler that do indeed remind us of Earth in size, orbit and temperature.”

What we don’t yet know is if they’re big balls of rock like Earth or central cores of rock surrounded by helium and hydrogen gases and maybe a thick ocean of water, Marcy said. The planets are 40 percent and 60 percent larger than Earth.

If they are gassy planets, like Saturn or Jupiter, there would be no land on which life could emerge and thrive.

“It’s possible that these planets have the right size and temperature but no land on which biology could get a toehold,” Marcy said.

Unknown is the mass, density or composition of the planets. Mass divided by size gives you density. And density would give us powerful clues to whether the planet is made of rock like Earth or of gas, like Jupiter or Saturn.

Earth has a density of 5.5 grams per cubic centimeter. Mars, with its dry desolate surface, inhospitable to life, has a density of 3.9 grams per cubic centimeter. The gassy Jupiter is 1.3 grams per cubic centimeter.

But the really humorous planet, Marcy says, is Saturn, a mere 7/10 of a gram per cubic centimeter.

“At 7/10 of a gram per cubic centimeter, Saturn would float in your bathtub,” Marcy said. “If, that is, you had a really, really, really large bathtub.”

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