NASA’s Kepler spacecraft, which discovered thousands of planets beyond the Solar System, has died at the age of nine.
The agency announced on 30 October that Kepler had run out of fuel and ceased its scientific mission. Before its demise, the telescope had downloaded all the data it had collected to mission control.
“It was the little spacecraft that could,” says Jessie Dotson, Kepler's project scientist at NASA’s Ames Research Center in Moffett Field, California. “It always did everything we asked of it, and more.”
With Kepler, “we have shown there are more planets than stars in this Galaxy”, says William Borucki, a now-retired space scientist who came up with the idea for the spacecraft.
Searching for starlight
The hard-working telescope soared into space aboard a Delta II rocket in March 2009. For four years, Kepler stared at more than 150,000 stars in the constellations Cygnus and Lyra, watching for flickers of starlight. From those tiny fluctuations, Kepler scientists deduced when planets were passing across the face of the stars as seen from Earth, temporarily dimming their light.
Mechanical failures hindered Kepler’s ability to orient itself in space in 2013. So NASA came up with a plan called K2 that directed the probe to look at a narrow slice of the sky aligned with the plane of the Solar System’s planets. The spacecraft’s renewed life enabled researchers to continue discovering planets, as well as to study nearby bright stars.
Between them, the Kepler and K2 missions discovered at least 2,681 confirmed planets. Among those are Kepler-186f, an Earth-sized planet in the habitable zone of its star, and Kepler-22b, one of many that turned out to be between the size of Earth and Neptune. Planets the size of Kepler-22b aren’t found in the Solar System, but they’re common throughout the Milky Way.
Nearly 2,900 further potential planets spotted by Kepler await confirmation.