Earlier this month, NASA’s planet-hunting Kepler Space Telescope began to get a little wobbly, a sign that the spacecraft was running out of fuel. Astronomers downloaded the spacecraft’s data and put it into “nap” mode to conserve energy. But the tank eventually ran dry. Now, NASA has announced that Kepler is officially retired and will spend its days distantly trailing Earth as it orbits the sun.
Kepler may be gone, but its legacy will live on in the 2,650 exoplanets the telescope spotted, which account for about 70 percent of all the worlds we know outside of our own solar system.
“As NASA's first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond,” Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate says in the statement. “Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.”
Kepler wasn’t designed to live as long as it did. Launched in 2009, the $600 million craft was originally designed using a 95 megapixel camera that stared at one spot in the constellation Cygnus, eying 150,000 stars for signs that planets circled them. It easily completed that primary mission. After four years in orbit, the craft experienced a malfunction that made it difficult to aim. Researchers took the opportunity to give Kepler a new mission, dubbed K2, in which it slowly rotated and scanned an even larger portion of the sky. In total, the craft examined 500,000 stars for signs of exoplanets.
Daniel Clery at Science reports that so far, Kepler’s data has revealed 2,650 planets, with more than 3,000 possible exoplanets still awaiting confirmation. Kepler has provided so much data on planets and stars that scientists will be poring over it for the next decade.
That will provide many new insights, but Kepler’s discoveries have already rocked the astronomy world. If the areas Kepler has examined are typical for the entire Milky Way, that means galaxy hosts 100 billion planets, an average of one planet for every star.
“Now, because of Kepler, what we think about the universe has changed,” NASA astrophysics division director Paul Hertz tells Mary Beth Griggs at The Verge. “Kepler opened the gate for the exploration of the cosmos.”
Getting to that point, however, was a struggle. Clery reports that the idea for the telescope came from NASA scientist William Borucki, whose proposal for a planet-hunting telescope was rejected four times before Kepler became a reality. Before Kepler, researchers had discovered a handful of giant exoplanets by looking for stars that showed signs that a close gas giant was tugging at them. Borucki wanted to broaden the search for smaller planets by using the transit method. By monitoring a star's brightness, Borucki believed researchers could find signs of planets as they orbited in front of the star, dimming it ever so slightly.The idea worked, but finding the planets meant digging into massive amounts of data.
“It was like trying to detect a flea crawling across a car headlight when the car was 100 miles away,” Borucki explained at a press conference about Kepler’s retirement.
Luckily, as Kepler winks out, its successor is already in orbit. Tom McKay at Gizmodo reports that in April, TESS, the Transiting Exoplanet Survey Satellite, was launched and should begin hunting for more planets soon. TESS is more powerful than Kepler, and it is expected to find over 20,000 new exoplanets. And after that, the long delayed successor to Hubble, the James Webb Space Telescope is expected to go into service in 2021 and will be powerful enough to give us our first actual images of exoplanets.