The galaxy just got more crowded. Astronomers using data from the Kepler space telescope have confirmed the existence of 715 new planets orbiting 305 stars, increasing the total number of known planets to about 1,700. This is the largest number of planet confirmations ever announced at once.
“We’ve struck the mother lode,” said Jack Lissauer, a planetary scientist at NASA’s Ames Research Center in Moffett Field, Calif., during a February 26 press conference. “It’s an exoplanet bonanza.”
The new planets are mostly small — 94 percent are no bigger than Neptune — and circle their stars along with sister planets in compact, circular orbits all in the same plane. The new findings increase the number of confirmed Earth-sized planets by 400 percent.
The planetary arrangements “remind us of home,” said Jason Rowe, an astronomer at the SETI Institute in Mountain View, Calif. “We’re seeing scaled-down versions of our solar system.”
The cache of confirmations more than doubles the number of planets established by the now-crippled Kepler since its 2009 launch (SN: 11/30/13, p.13). Kepler searched for planets by looking for tiny dips in starlight that occur when a planet periodically passes in front of, or transits, its star. However, transiting planets aren’t the only reason stars appear to flicker. Most commonly, the light dips can be caused by a chance alignment with an “eclipsing binary” — a pair of stars that orbit each other and one occasionally blocks the light from the other.
For the new findings, mission scientists argued that several detections around a single star are not likely to be false positives. “It’s very, very exciting to see this result,” says Rory Barnes, an astronomer at the University of Washington in Seattle. The reasoning behind the team’s argument is sound and based on solid mathematics, which they’ve been perfecting for several years, he adds.
The Kepler scientists calculated that eclipsing binaries would be very unlikely to cause multiple dips in a star’s light. While one eclipsing binary getting in the way is possible, two isn’t likely. Three or four is nearly impossible. Because astronomers were seeing many more stars that seemed to have multiple planets than expected from random alignments with binaries, nearly all must be actual solar systems, the researchers reasoned. The scientists describe their confirmation techniques and findings in two papers posted February 26 at arXiv.org.
To confirm previous exoplanet candidates as real, a team needed many months with a ground-based telescope for each. “Do the math,” says Sarah Ballard, an astronomer also at the University of Washington. With the more than 3,600 candidates that Kepler has identified, that’s a staggering amount of work. Now, astronomers can confirm exoplanet systems in bulk. “It’s like the Costco of planet validation,” she adds.
The next step for the Kepler team is to pore over the rest of their data. The 715 new planets emerged from only the first two years of observations. But Kepler kept observing for an additional two years before the second of its four reaction wheels, which are needed to accurately point the telescope, failed in May 2013 (SN: 6/15/13, p. 10). With another two years of data to sift through, mission scientists are confident that this technique will turn up hundreds more exoplanets.
Meanwhile, astronomers now have an additional 300 solar systems to mull over. The compactness of these systems along with the prevalence of small planets is surprising. Theorists will stay busy figuring out why planets stop growing after reaching the size of Earth or Neptune and how all these worlds end up huddling close to their suns. But Kepler is more sensitive to planets with compact orbits, so it’s too early to say whether this type of arrangement is the norm.
Previously discovered exoplanets tended to be larger than the new finds, making clear that the galaxy is littered with an enormous diversity of planetary systems.
Editor’s Note: This story was updated on March 18, 2014, to correct the number of planet candidates Kepler has identified.