The Milky Way galaxy feels a little more crowded.
Sifting through data from NASA’s Kepler space telescope, scientists said Tuesday they’ve confirmed the existence of 1,284 planets orbiting other stars.
The announcement more than doubles the number of validated planets discovered by the planet-hunting spacecraft, bringing the total number to about 2,325.
This bumper crop of new worlds features a host of super-Earths and mini-Neptunes. Perhaps most striking, the new census includes nine worlds that could be rocky and Earth-like and orbit their host stars in the so-called habitable zone, where temperatures would allow water to be stable in liquid form.
“This gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth,” NASA chief scientist Ellen Stofan said in a statement.
The findings, published Tuesday in the Astrophysical Journal, also present a new technique to validate candidate planets that should vastly speed up the verification process.
During Kepler’s primary mission, the spacecraft stared at a single patch of sky containing roughly 150,000 sun-like stars. It looked for the tiny dips in starlight caused by a planet passing in front of it.
From its launch in 2009 to the crippling of its second reaction wheel in 2013, Kepler identified more than 4,500 possible exoplanets of all sizes, from super-Jupiters to Mars-sized worlds.
But many different celestial phenomena can mimic a transiting planet. A brown dwarf or other dim star might pass in front of a larger one. A binary system, in which two stars circle each other, can also fool Kepler’s unblinking eye.
So researchers have had to go to great lengths to confirm each candidate exoplanet on a case-by-case basis, following up with observations from ground telescopes and using techniques that are tailored for each situation.
“One of the biggest challenges for Kepler is that these follow-up observations that have been traditionally used to verify planets are time- and resource-intensive,” said Timothy Morton, an associate research scholar at Princeton University and lead author of the new scientific report.
So Morton devised an algorithm that uses the power of probability to speed up the process. It combines two ideas — how well does the observed signal resemble that of a real planet, and how common are fakes — to conduct a detailed analysis that can confirm planets with a roughly 99 percent reliability.
The scientists also used it to verify 984 exoplanets that had already been confirmed using other techniques.
The batch of newly confirmed worlds includes relatively fewer Jupiter-sized planets, which were plentiful in the early days of the Kepler mission. In part, that’s because their large size caused dramatic dips in starlight that were easier for the telescope to see. Also, they were often found surprisingly close to their stars, which meant they orbited very quickly and provided more transits for scientists to analyze.
Since gathering all this data, the Kepler spacecraft has moved on from its single patch of sky to gazing at other parts of the galaxy. This K2 mission will last for about another year and a half, when the spacecraft is expected to run out of fuel, said mission manager Charlie Sobeck.
But scientists are already looking forward to the Transiting Exoplanet Survey Satellite, or TESS, NASA’s follow-up to Kepler that is set to launch in 2017.