18 Earth-size planets found in our galaxy—all hiding in plain sight

And a hundred more small worlds may be awaiting discovery, astronomers predict, thanks to a new method for combing through NASA data.

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An exoplanet orbits its host star in an illustration. A fresh look at information captured by NASA's planet-hunting Kepler telescope revealed an additional 18 worlds hiding in the data.

Since its launch a decade ago, NASA’s planet-hunting Kepler spacecraft has found thousands of worlds, revealing that across the galaxy, planets are more numerous than stars.

But even though Kepler is done collecting data, scientists are still finding treasures in its vaults, including 18 new, relatively small worlds. Many of these previously overlooked planets are similar to Earth in size, and one of them even lives in an orbit that could be life-friendly.

“I’m excited, but not surprised,” says Caltech’s Jessie Christiansen of the results, reported in two Astronomy and Astrophysics publications. “It was inevitable that improved searches of the data would uncover previously undetected small planets.”

I can show you the worlds

From 2009 to 2013, Kepler stared at a single patch of starry sky, watching for the footprints of planets marching across their stars’ faces. To Kepler, these planetary transits looked like a brief dimming of starlight, and from those blips in brightness, called light curves, scientists can calculate a planet’s size and orbit.

When an on-board malfunction crippled the spacecraft and it could no longer stare at that single patch of sky, Kepler scanned more of the heavens, rebirthed as the K2 mission, until the spacecraft ran out of fuel in late 2018.

At the mission’s conclusion, the Kepler team announced its official haul. For the primary Kepler mission, that was some 2,300 confirmed planets and 2,400 more candidates. The K2 mission added 500 or so planets and candidates.

It’s this second data set that attracted the...

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