Published: Wed, October 31, 2018
Research | By Raquel Erickson

The Kepler space telescope's end has finally come

The Kepler space telescope's end has finally come

After nine years in deep space collecting data that indicate our sky to be filled with billions of hidden planets, NASA's Kepler space telescope has run out of fuel needed for further science operations.

The end came just a few months shy of the 10th anniversary of Kepler's 2009 launch.

"We have shown that there are more planets than stars in our galaxy", Borucki said. "Some of those, in fact, might be actual water worlds. Imagine what life might be like on such planets". "That was an fantastic diving catch", said Paul Hertz, astrophysics division director at NASA Headquarters.

"Before we launched Kepler, we didn't know if planets were common or rare in our galaxy", he said.

The far more advanced James Webb Space Telescope, scheduled to lift off in 2021, should be able to reveal more about planets' mass, density and the makeup of their atmosphere - all clues to habitability. When scientists factored those finds into statistical formulas that take Kepler's limitations into account, they concluded that 20 to 50 percent of the Milky Way's stars may have rocky planets in habitable zones.

Of that total, the science team picked some 300,000 that were the right age, composition and brightness to host Earth-like planets.

Mission planners reworked Kepler's mode of operation to point at other parts of the sky, expanding its list of targets to 500,000 stars.

The spacecraft's camera was not created to take pictures like other space telescopes.

It used a detection method called transit photometry, which looked for periodic, repetitive dips in the visible light of stars caused by planets passing, or transiting, in front of them.

Bill Borucki, the mission's retired principal investigator, compared the task to "trying to detect a flea crawling across a auto headlight when the vehicle was 100 miles away".

Borucki, who dreamed up the mission decades ago, said one of his favourite discoveries was Kepler 22b, a water planet bigger than Earth but where it is not too warm and not too cold - the type "that could lead to life".


On July 14, 2012, one of the reaction wheels failed, leaving the spacecraft without a backup.

Stylized artwork shows NASA's Kepler space telescope among planetary systems.

But all of that took rocket fuel, and last June, engineers saw a major drop in fuel tank pressure, indicating the spacecraft's tank was almost empty.

Signals that fuel was almost out were seen two weeks ago. The sequence of commands for doing so has been transmitted to the spacecraft, awaiting a final command from the ground to run them.

"In the end, we didn't have a drop of fuel left over for anything else", Charlie Sobeck, project system engineer at NASA's Ames Research Center, said during a teleconference. "While this may be a sad event, we're by no means unhappy with the performance of this marvelous machine".

Kepler's nine-and-a-half-year flight was more than twice as long as originally planned. "It always did everything we asked of it, and sometimes more".

Kepler was succeeded by NASA's Transiting Exoplanet Survey Satellite, or TESS, which was launched in April.

The resurrected mission became known as K2 and yielded 350 confirmed exoplanets, or planets orbiting other stars, on top of what the telescope had already uncovered since its March 7, 2009, launch from Cape Canaveral.

"It has revolutionized our understanding of our place in the cosmos", Hertz said.

"I'm excited about the diverse discoveries that are yet to come from our data and how future missions will build upon Kepler's results".

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