After nine years in deep space, NASA officially bid farewell to the Kepler telescope. The spacecraft revealed a universe full of planets.

The most prolific planet-hunting machine has run out of fuel. The American space agency has decided to retire the spacecraft within its current, safe orbit, away from Earth.

“Science operations are over,” NASA astrophysics division director Paul Hertz told reporters on a conference call.

Kepler’s catalog of confirmed planets includes over 2,600 worlds and dozens that could potentially support alien life. That’s 70 percent of the 3,800 confirmed alien worlds to date.

However, the announcement wasn’t a surprise. The planet-hunting machine has been running low on fuel for months. Therefore, mission managers had to put the spacecraft to sleep several times recently to extend its operational life as much as possible.

The spacecraft detected planets by looking for their transits. This is when a planet passes between its star and Earth. Thus, causing a small dip in the light of the star.

“It was like trying to detect a flea crawling across a car headlight, when the car was 100 miles away,” William Borucki, retired Kepler principal investigator said in a press conference today.

The most recent analysis of Kepler’s discoveries concludes that 20 to 50 percent of the stars visible in the night sky are likely to have small, possibly rocky, planets similar in size to Earth, and located within the habitable zone of their parent stars.

What’s next?

While the telescope has stopped collecting new data, Hertz says astronomers are still working with what they have collected over the years.

“Kepler data will continue to yield scientific discoveries for years to come.”

One of Kepler’s successors is currently in space and searching for new planets. NASA’s Transiting Exoplanet Survey Satellite has already spotted its first pair of Earth-like planets and will continue to do so.

However, scientists hope that the upcoming James Webb Space Telescope will be able to take a much closer look. Perhaps even look for signs of life on the worlds that TESS and Kepler have pinpointed.

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Thumbnail image: Artist’s concept of NASA’s Kepler space telescope. Credit: NASA