Earth Cousin

Maude, I love this stuff:

It is a bit bigger and somewhat colder, but a planet circling a star 500 light-years away is otherwise the closest match of our home world yet discovered, astronomers announced on Thursday.

The planet, known as Kepler 186f, named after NASA's Kepler planet-finding misison, which found it, has a diameter of 8,700 miles, 10 percent wider than Earth, and its orbit lies within the "Goldilocks zone" of its star, Kepler 186 — not too hot, not too cold, where temperatures could allow for liquid water to flow at the surface, making it potentially hospitable for life.

"It's Earth size," said Elisa V. Quintana of the SETI Institute and NASA's Ames Research Center in Mountain View, Calif. "It's in the habitable zone. So we now know these planets do exist."

...With its smaller size, Kepler 186f is more likely to have an Earth-like rocky surface, another step in astronomers' quest for what might be called Earth 2.0.

"It's a progression," said another member of the discovery team, Thomas S. Barclay of the Bay Area Environmental Research Institute. "This is a very, very exciting milestone discovery. It has a much higher probability of being habitable. This planet really reminds us of Earth."

The researchers speculate that it is made of the same stuff as Earth. "It probably has a composition made up of iron and rock and ice and some water, as Earth does," Dr. Barclay said, though he added that "the relative combination of those things could be very different."

The gravity on Kepler 186f, too, would be roughly the same as Earth's. "You could far more easily imagine someone being able to go there and walk around on the surface," said Stephen Kane, an astronomer at San Francisco State and another member of the research team.

Kepler 186f is not a perfect replica, however. It is closer to its star — a dwarf star that is smaller and cooler than the sun — than the Earth is, and its year, the time to complete one orbit, is 130 days, not 365. It is also at the outer edge of the habitable zone, receiving less warmth, so perhaps more of its surface would freeze.

On the other hand, the researchers said that with its greater mass, Kepler 186f could conceivably have a thicker, insulating atmosphere to compensate.

"Perhaps it's more of an Earth cousin than an Earth twin," Dr. Barclay said.

Yay! Now we can totally go there once we've ruined this planet! It turns out the nefarious alien aggressors from the movies who travel the universe invading and exploiting like-planets after destroying their own are us!

Just kidding! We'll definitely destroy Earth before we figure out how to leave it! You're safe, inhabitants of Kepler 186f!

(In all seriousness: Neat!)