NASA's Kepler space telescope, which has been taking a galactic census, just verified a whopping 1,284 new planets—the most ever announced in one go, scientists said on Tuesday. This planetary bounty more than doubles the number of confirmed planets that Kepler has already found, and some of them are thought to be Earthlike.
When scientists seek out other planets where life could exist, they look for rocky, wet, temperate worlds like our own. Of these new planets, almost 550 are small enough that they could be rocky, not inhospitable gas giants like Jupiter. Nine are orbiting in their sun's habitable zone, and so they might have liquid water at the surface.
Altogether, we now know of 21 exoplanets that are relatively small, rocky, and orbiting in the "Goldilocks" zone around their star. It's imaginable that some could host life.
Scientists analyzed data from Kepler's prime mission, which ran from 2009 to 2013—four years it spent gazing unblinkingly at 150,000 stars, watching for tiny dips in light that could indicate a planet had slipped in front of it.
All these "planet candidates" had to be confirmed as real, actual planets—and not just false positives—which is often done through ground-based observation, including radial velocity. Following up on all these planets is time consuming, explained Tim Morton of Princeton University, lead author of the new study, in The Astrophysical Journal.
"It's taken about 15 years of hard work to confirm 200 planets from the ground," he said.
Morton's new method is a way for researchers analyze thousands of signals at once, through an automated technique that assigns each planet candidate a "planethood probability percentage," and performs an automated computation, the first time an automated process like this has been used on such a large scale, to a reliability greater than 99 per cent.
By now, scientists have found about 5,000 possible exoplanets outside our solar system, and more than 3,200 have been verified, according to NASA. The Kepler mission deserves the lion's share of the credit, because 2,325 of these have been found by Kepler.
Kepler/K2 mission manager Charlie Sobeck, who spoke to media on Tuesday, predicts it could keep running for another two years. The K2 mission, which started after Kepler suffered a glitch and had to change courses in 2013, "is ultimately going to be constrained by fuel," he said, predicting it will run out in the summer of 2018.
Other telescopes are planned, like the Transiting Exoplanet Survey Satellite (or TESS), which launches in 2017, as a sort-of follow-up to Kepler: it will also be looking for planets transiting stars. The James Webb Space Telescope, scheduled to launch in 2018, will be able to study the atmospheres of distant planets, something Kepler can't do, which will give scientists an even better idea of whether life could exist on a distant planet.
Kepler has changed the way we understand the galaxy, and our place in it. As little as two decades ago, we didn't know for sure if there were any planets outside our solar system, and now we know that planets orbit practically every star in the sky.
"You're talking about tens of billions of potentially habitable, Earth-size planets out there in the galaxy," said Kepler mission scientist Natalie Batalha. One day, maybe not too long from now, we'll be able "to look up and point to a point of light and say, That star has a living world orbiting it."