Kepler, NASA’s venerable planet-hunting telescope, is officially going offline. Permanently.
We knew this day was coming. NASA warned that Kepler’s demise was , citing a shortage of fuel as it neared a decade of service—almost three times its original expected lifespan of 3.5 years—since launching in 2009.
"We found the [fuel] pressure dropped significantly, from 90 psi to 30, and this really marked the rest of the fuel we had," Jeff Coughlin, a SETI Institute scientist who works on the Kepler mission, told Seniorhelpline.
The last of the fuel was used to great effect: It stabilized the craft enough to get its final data downlinked. "We were able to squeeze out every last bit of data and get everything on the ground," Coughlin says. "Now, we’ll turn off the transmitters so we don’t pollute space and see a signal coming from beyond Earth anymore."
That remaining data from Kepler is huge—as is the potential for what it will reveal. The first Kepler mission spent 2009 to 2013 staring at the same patch of sky near the Cygnus constellation, leading to the identification of 2,327 formerly unknown planets beyond our galaxy. More than 2,400 possible planets still await confirmation from that time period.
Kepler finds planets by looking for small dimming events called transits, which happen when a planet passes in front of its star (from Earth's perspective), causing a slight dimming of the planet. "It was like trying to detect a flea crossing a car headlight when the car was 100 miles away," William Borucki, the former principal investigator of Kepler, said in a press conference.
Toward the end of its first mission, two of Kepler's reaction wheels failed and the craft could no longer stabilize its instruments. Keeping those instruments pointed at their targets was essential, so Kepler couldn’t continue on without the wheels, explained Jessie Dodson, Kepler project scientist, in a press conference.
That could have spelled the end of the mission, but the scientists running the telescope used pressure from sunlight and strategically used fuel to regain its balance. They dubbed this new mission K2, which found another 354 planets, with 473 additional candidates awaiting confirmation today. Coughlin says that there are probably 1,000 more candidates to be found in the K2 data.
The biggest takeaway from Kepler was that almost every star seems to have a planet. Of the stars it found, many had multiple planets—which would indicate that planets far outnumber stars. Twenty to 50 percent of the located stars appeared likely to have Earth-like, habitable planets, which is good news if you're hoping to eventually have alien friends.
Still, Kepler served as more than just a planet spotter, Coughlin says. Because Kepler stared at the same patch of sky with specialized instruments that read brightness of celestial objects, it was also able to capture undiscovered asteroids, supernova explosions, and galaxies with variable light output. The supernovae were especially remarkable, as the craft was capable of catching them just as they exploded. Few supernovae have ever been caught at that stage.
Though Kepler may be gone, NASA has another planet-finding mission called Transiting Exoplanet Sky Survey (TESS). Unlike Kepler, TESS will search the entire sky, with a primary focus on planets within 300 light-years from Earth.
Again, good new if you're hoping to eventually befriend a few aliens. "From the SETI side, we’re always trying to figure out how many civilizations exist in the galaxy that we could even talk to," Coughlin says. "Thanks to Kepler, we know they’re common."