Scientists from Princeton University and NASA have confirmed that 1,284 objects observed outside Earth's solar system by NASA's Kepler spacecraft are indeed planets. Reported in The Astrophysical Journal on May 10, it is the largest single announcement of new planets to date and more than doubles the number of confirmed planets discovered by Kepler so far to more than 2,300.
The researchers' discovery hinges on a technique developed at Princeton that allows scientists to efficiently analyze thousands of signals Kepler has identified to determine which are most likely to be caused by planets and which are caused by non-planetary objects such as stars. This automated technique -- implemented in a publicly available custom software package called Vespa -- computes the chances that the signal is in fact caused by a planet.
The researchers used Vespa to compute the reliability values for over 7,000 signals identified in the latest Kepler catalog, and verified the 1,284 planets with 99 percent certainty. They also independently verified more than 700 additional planet signals that had already been confirmed as planets by other methods. In addition, the researchers identified 428 candidates as likely "false positives," or signals generated by something other than a planet.
Timothy Morton, lead author of the study and a Princeton associate research scholar of astrophysical sciences, developed Vespa because the vast amount of data Kepler has gathered since its 2009 launch has made the traditional method of confirming planets by direct ground-based follow-up observation untenable, he said. Follow-up observations of Kepler data had confirmed a little more than a thousand planets prior to the Princeton-NASA announcement.
"Vespa is a culmination of a change in attitude about how we deal with these large-data surveys," Morton said. "This new problem Kepler created is that we now have thousands of new planet candidates. Astronomers knew we couldn't follow up all of these in the traditional way, but there was nothing to replace it. This result now puts a number on exactly how likely it is that each detected object is a planet."
Kepler, which ended data collection for its primary mission in 2013, operated by precisely measuring the brightness of many stars simultaneously. The satellite looked for stars that exhibited subtle and regular dimming, which indicates that an orbiting planet is passing in front of, or transiting, that star.