NASA’s Kepler Spacecraft Discovers 2 Earth-Size Planets

NASA's Kepler mission announces that it's found two planets circling another star, the first ever that are Earth's size or smaller. In this artist's conception, the planet Kepler-20f, which could have an atmosphere of water vapour, is compared to Earth. (Courtesy Tim Pyle via Nature)

In what amounts to a kind of holiday gift to the cosmos, astronomers from NASA’s Kepler spacecraft announced Tuesday that they had discovered a pair of planets the size of Earth orbiting a distant star.

The new planets, one about as big as Earth, the other slightly smaller than Venus, are the smallest planets yet found beyond the solar system. Unfortunately, they are not in the 'Goldilocks' zone.

Astronomers said the discovery showed that Kepler could indeed find planets as small as our own and was an encouraging sign that planet hunters would someday succeed in the goal of finding Earth-like abodes in the heavens.

Since the first Jupiter-size exoplanets, as they are known, were discovered nearly 15 years ago astronomers have been chipping away at the sky, finding smaller and smaller planets.

“We are finally there,” said David Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics, who was a member of the team that made the observations, led by his colleague Francois Fressin.

The team reported its results in an online news conference Tuesday and in a paper being published in the journal Nature.

The announcement doubled the number of known Earth-size planets in the galaxy to four from two — Earth and Venus.

The next major goal in the planetary hunt, astronomers say, is to find an Earth-size planet in the so-called Goldilocks zone of a star, where conditions are temperate for water and thus life.

The two new planets, called Kepler 20e and Kepler 20f, are far outside the Goldilocks zone — so close to the star, termed Kepler 20, that one of them is roasting at up to 1,400 degrees Fahrenheit — and are thus unlivable.

Although the milestone of an Earth-size planet had long been anticipated, astronomers on and off the Kepler team were jubilant.

Geoffrey Marcy of the University of California, Berkeley, another Kepler team member, called the new result “a watershed moment in human history.”

Debra Fischer, a planet hunter from Yale, who was not part of the team, said, “This technological feat is incredibly important because it means that the detection of Earth-sized planets at larger distances is technically possible


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