National Geographic Daily News
An illustration of an exoplanet and its parent star.

An artist's conception of the Kepler-10 star system, which includes two alien planets.

Illustration courtesy T. Pyle, NASA/Caltech

Ker Than

for National Geographic News

Published March 2, 2012

More than a thousand potential new planets have been found outside our solar system—nearly doubling the number of candidates discovered so far by NASA's Kepler space telescope, according to a new study.

The fresh batch of Kepler Objects of Interest, or KOIs, emerged from an analysis of mission data gathered between May 2009 and September 2010.

The data revealed 1,091 possible new planets, bringing the total count to 2,321—up from 1,235 candidates formally announced last February.

(Also see "'Solar Systems' Common Across the Galaxy, NASA Probe Hints.")

What's more, "we have a statistical reason to think at this point that something like 90 percent of them are probably real planets," said study co-author Ronald Gilliland, an astronomer at Pennsylvania State University and a member of the Kepler team.

So far, the Kepler team has confirmed the existence of 61 alien planets, including an Earthlike world that orbits its star at the right distance for life.

Zeroing In on Earth's Twin

Aside from the sheer number of new candidates, astronomers are excited that a substantial fraction of the haul appears to be made up of small, cool worlds that are more similar to Earth than many of the previous finds.

For example, Kepler's latest discoveries include 196 new Earth-size planet candidates, nearly quadrupling the number of similar candidates announced last year.

(Related: "NASA's Kepler Finds Two Earth-Size Planets Around Sunlike Star.")

The number of potential super-Earths—planets that are about two times the mass of Earth—also saw a big jump, with 416 new candidates announced.

The trend toward finding smaller worlds in the Kepler data suggests that the spacecraft, launched in March 2009, may finally be nearing its goal of spotting true Earth analogs capable of supporting liquid water—and perhaps life.

"To be able to detect analogs of Earth, which by definition have a one-year [orbital] period, you have to do observations for a few times during that one-year period," Gilliland explained.

How You Can Help Confirm a New Planet

Before they can be recognized as true planets, though, the new KOIs must go through a rigorous confirmation process that can take from six months to a year.

(Related: "Smallest Exoplanets Found-Each Tinier Than Earth.")

One major concern for astronomers is that what looks like a planet may in fact be a false positive created by eclipsing stars or some other phenomena.

The Kepler team has developed software to rule out these alternative explanations, but members of the public can also help by joining citizen-science projects that sift through Kepler data, such as planethunters.org.

"The team very much appreciates that there's a large enthusiastic community interested in doing this," Gilliland said.

A paper describing the possible new planets was published online this week at arXiv.org and has been submitted for publication in the Astrophysical Journal.

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