The Kepler mission has verified 1,284 new planets – the single largest finding of planets to date – and nearly 550 could be rocky planets like Earth.
“This announcement more than doubles the number of confirmed planets from Kepler,” said Ellen Stofan, chief scientist at NASA Headquarters in Washington.
“This gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth.”
The Kepler space telescope identifies candidates for planet status by capturing the signals of decreases in brightness that occur when planets pass in front of, or transit, their stars.
The researchers analyse the results to verify suspected planets.
Kepler’s July 2015 planet candidate catalogue identified 4,302 potentials, which, when analysed, left 1,284 candidates with the probability of being a planet is greater than 99% – the minimum required to earn classification.
An additional 1,327 candidates have a less than 99% probability but are still more likely than not to be planets.
The remaining 707 are more likely to be some other astrophysical phenomena. This analysis also validated 984 candidates previously verified by other techniques.
In the past scientists have had to study each candidate one by one, but this latest announcement is based on a statistical analysis method that can be applied to many planet candidates simultaneously.
Timothy Morton from Princeton University in New Jersey and lead author of the paper describing the work published in The Astrophysical Journal employed a technique to assign each Kepler candidate a planet-hood probability percentage.
“Planet candidates can be thought of like breadcrumbs,” Morton said.
“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.”
Of the newly identified planets, some 550 could be rocky planets like Earth, based on their size. Nine of them orbit in their sun’s habitable zone, the so-called Goldilocks Zone, not too hot and not too cold, where the surface temperatures allow liquid water to pool.
With the addition of these nine, 21 exoplanets now are known to be members of this exclusive group.
“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,” said Natalie Batalha, co-author of the paper and the Kepler mission scientist at NASA’s Ames Research Centre in Moffett Field, California.
Of the nearly 5,000 total planet candidates found to date, more than 3,200 now have been verified and 2,325 of these were discovered by Kepler.
“Before the Kepler space telescope launched, we did not know whether exoplanets were rare or common in the galaxy. Thanks to Kepler and the research community, we now know there could be more planets than stars,” said Paul Hertz, an astrophysicist at NASA.
“This knowledge informs the future missions that are needed to take us ever-closer to finding out whether we are alone in the Universe.”
Bill Condie is a science journalist based in Adelaide, Australia.
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