Science Scope

Getting closer and closer to finding an Earth-like planet

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This year marked the discoveries of several planets that resemble Earth in various ways, bringing us ever closer to finding a truly Earth-like planet.

If, as they say, the world will end in 2012, it could be just as we are on the verge of finding a planetary twin to Earth.

The year 2011 has been notable for numerous findings of more and more planets with characteristics that make them similar to Earth.

These milestones culminated in the December 20 discovery of two Earth-sized planets orbiting a star.

“The primary goal of the Kepler mission is to find Earth-sized planets in the habitable zone," said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., lead author of a new study published in the journal Nature. "This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them.”

NASA's Kepler mission, a space telescope whose charge is to possible planets, discovered the newfound ones, called Kepler-20e and Kepler-20f. Kepler-20e is slightly smaller than Venus (which itself is slightly smaller than Earth), and Kepler-20f is a bit larger than Earth.

But don't think about moving to either one anytime soon. The Earth-size planet, Kepler-20f is a scorching 800°F (427°C), while the Venus-sized Kepler-20e is a blistering 1,400°F (760°C). And anyway, the planets are 950 light-years away, orbiting the star Kepler-20.

They are also different from Earth in that they are wound tightly around Kepler-20; Kepler-20e orbits around it in 6.1 days, and Kepler-20f in 19.6 days.

As you might guess from their names, they aren't the only planets orbiting their sun. There are Kepler-20 b, c and d (a is reserved for the star itself). The arrangement of the planets is quite different from our solar system, in which the small planets orbit closely to the sun and the big planets are farther away. The Kepler-20 system is not as neatly designed: The closest planet is big, the second is small, the third is big, etc.

The discovery of Keplers-20e and f capped off a year that began with the discovery of the first rocky planet outside of our solar system, Kepler-10b, and continued with the first discovery of the first planet in a "habitable zone" (the region where liquid water could exist on a planet’s surface), Kepler-22b, announced December 5. But Kepler-22b is 2.4 times the size of Earth.

With each new discovery, the Kepler spacecraft gets closer to its goal of finding planets similar to Earth as it scans 150,000 stars to find ones like the sun that have planets of the same size orbiting at about the distance of Earth from our sun.

As David Charbonneau, a Harvard astronomer who was part of the team that discovered Keplers-20e and f, told Time:

Two weeks ago, we announced a planet in its star's habitable zone but which was much bigger than Earth. Today, we're announcing a planet that's the same size as Earth. What we want is the best of both — a true twin of Earth. Hopefully, well find it within the next year.

And hopefully, that will happen before the 2012 apocalypse.

Related on SmartPlanet:

photo: A comparison of Earth and Venus to the first Earth-size planets, Kepler-20e and Kepler-20f, found around a sun-like star. (NASA/Ames/JPL-Caltech)

via: Time, NASA

Laura Shin

Features Editor

Laura Shin has been published in The New York Times, The Wall Street Journal and The Los Angeles Times, and is currently a contributor at Forbes. Previously, she worked at Newsweek, the New York Times, Wall Street Journal and LearnVest. She holds degrees from Stanford University and Columbia University's Graduate School of Journalism. Follow her on Twitter. Disclosure