Scientists say that they’ve now confirmed that 1,284 objects observed outside Earth’s solar system by NASA’s Kepler spacecraft are indeed planets. Announced yesterday (May 10, 2016) in the Astrophysical Journal, it’s 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 2,325.
And it means that – of the nearly 5,000 total exoplanet candidates found to date – more than 3,200 have been verified (2,325 by Kepler, and the rest by other means). Go Kepler!
Ellen Stofan is chief scientist at NASA Headquarters in Washington. She said:
This announcement more than doubles the number of confirmed planets from Kepler. This gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth.
The Kepler mission finds planets by the transit method; that is, it looks for a brief dip in a star’s light as planets previously hidden in their stars’ glare pass in front of the stars (much like the May 9 Mercury transit across the face of our sun). False positives are common. They can result from – for example – smaller, dimmer stars orbiting larger, brighter companion stars.
That’s why validation is needed.
During the May 10 announcement, the scientists explained a new technique developed by Princeton astrophysicist Timothy Morton, who is lead author of the Astrophysical Journal paper. It’s a statistical analysis method that can be applied to many planet candidates simultaneously. Morton’s method essential compares values from previous exoplanet observations to current measurements. Writing in Wired, Nick Stockton explained:
His method uses paired simulations, comparing values from previous exoplanet observations to current measurements. The first compares the flicker in question to other confirmed signatures of both exoplanets and imposters. The second simulation determines whether—given what scientists know about the total distribution of exoplanets in the Milky Way—the flicker in question makes sense as an exoplanet. Combined, the two simulations assign each flicker a statistical probability of being an exoplanet.
Timothy Morton said:
Planet candidates can be thought of like bread crumbs. If you drop a few large crumbs on the floor, you can pick them up one by one. But, if you spill a whole bag of tiny crumbs, you’re going to need a broom. This statistical analysis is our broom.
Scientists from Princeton University and NASA analyzed the Kepler space telescope’s July 2015 planet candidate catalog, which identified 4,302 potential planets. For 1,284 of the candidates, the probability of being a planet is now greater than 99 percent – the minimum required to earn the status of “planet.” An additional 1,327 candidates are more likely than not to be actual planets, but they do not meet the 99 percent threshold and will require additional study. The remaining 707 are more likely to be other astrophysical phenomena. This analysis also validated 984 candidates previously verified by other techniques.
In the newly-validated batch of planets, nearly 550 could be rocky planets like Earth, based on their size. Nine of these orbit in their sun’s habitable zone, which is the distance from a star where orbiting planets can have surface temperatures that allow liquid water to pool. With the addition of these nine, 21 exoplanets now are known to be members of this exclusive group.
Natalie Batalha is co-author of the paper and the Kepler mission scientist at NASA’s Ames Research Center in Moffett Field, California. She said:
They say not to count our chickens before they’re hatched, but that’s exactly what these results allow us to do based on probabilities that each egg (candidate) will hatch into a chick (bona fide planet).
This work will help Kepler reach its full potential by yielding a deeper understanding of the number of stars that harbor potentially habitable, Earth-size planets – a number that’s needed to design future missions to search for habitable environments and living worlds.
Bottom line: 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.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.