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27 Feb 2014
New analysis of data collected by the NASA space observatory verifies hundreds of small-sized planets.
Planet hunters analyzing the first two years of observations captured by NASA’s Kepler space telescope have found more than 700 planets orbiting 305 distant stars.
Using a technique known as “multiplicity” to verify that candidate planets were just that – and not, for example, pairs of stars in binary orbits – the NASA team’s findings increases the total number of known exoplanets to nearly 1700.
The newly-verified worlds include a number of multi-planet systems similar to our own solar system, with the vast majority of planets found to be smaller than Neptune, which is around four times the size of Earth.
The work also means a large increase in the number of exoplanets that are similar in size to Earth, and demonstrates the ongoing usefulness of the Kepler telescope, despite its faulty pointing mechanism.
Multiplicity analysis
Launched in 2009 with what, at the time, was the largest array of CCD sensors ever produced for a space mission, Kepler collected photometric data on nearly 200,000 stars for four years before problems with two reaction wheels reduced its pointing stability.
However, that photometric data is rich with information. A team co-led by Jack Lissauer, a planetary scientist at NASA's Ames Research Center in Moffett Field, California, used it to analyze stars with more than one potential planet, all of which were detected in the first two years of Kepler's observations – between May 2009 and March 2011.
The multiplicity technique relies in part on the logic of probability, says NASA. Of the tens of thousands of stars monitored by Kepler, a few thousand were found to have planet candidates. If the candidates were randomly distributed among those stars, only a handful would have more than one planet candidate. However, Kepler observed hundreds of stars that have multiple planet candidates. Studying this sample has confirmed the 715 “new” exoplanets.
"Four years ago, Kepler began a string of announcements of first hundreds, then thousands, of planet candidates - but they were only candidate worlds," said Lissauer. "We've now developed a process to verify multiple planet candidates in bulk to deliver planets wholesale, and have used it to unveil a veritable bonanza of new worlds."
Habitable zone
Before the latest findings, the vast majority of discovered exoplanets were giant planets on the scale of Jupiter. But the new analysis shows the existence of around 150 exoplanets that are similar in size to Earth – four times more than had been discovered previously.
Four of the newly discovered worlds are in orbits comparable with Earth’s own “habitable zone”, raising the possibility that liquid water and perhaps even life might be present there.
"The Kepler team continues to amaze and excite us with their planet hunting results," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate. "That these new planets and solar systems look somewhat like our own, portends a great future when we have the James Webb Space Telescope in space to characterize the new worlds.”
One of these new habitable-zone planets, known as “Kepler-296f”, orbits a star half the size and 5 percent as bright as our sun. Kepler-296f is twice the size of Earth, but scientists do not know whether the planet is a gaseous world, with a thick hydrogen-helium envelope, or if it is a water world surrounded by a deep ocean.
The latest findings come from the analysis of the first two years’ worth of Kepler data, and the verification of hundreds more exoplanets is expected once the full four-year dataset is interrogated.
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