Illustration of NASA's Kepler Space Telescope, which has discovered more than 2,650 exoplanets so far. Kepler has little fuel and has returned to sleep mode, mission team members announced on August 24, 201
Credit: W Stenzel / NASA Ames
The Most Successful Planet Hunter Instrument Ever Closed (19659005) NASA's Kepler Space Telescope, which has discovered about 70 percent of all known alien worlds to date, consumes very little fuel. At the beginning of July, Kepler purposely went into a hibernate state to make sure the spacecraft had enough fuel to align himself with the earth and send his latest data home four weeks later.
Such possibilities of data transmission occur in limited windows; Kepler and many other far-flung NASA spacecraft have to take turns using the agency's Deep Space Network, a system of great radio gear around the world. [Gallery: A World of Kepler Planets]
The Kepler data actually landed as planned in early August. But Kepler has fallen asleep again, and the future of the observatory is bleak, mission team members said today (August 24).
"It is unclear how much fuel is left on board, the health of the spaceship and the determination of a whole range of options and next steps," wrote members of the mission team in the update.
The $ 600 million Kepler spacecraft launched in March 2009 to determine how Earth-like planets behave everywhere in the galaxy. The telescope finds extraterrestrial worlds by identifying the tiny differences in brightness that they cause when they cross the faces of their guest stars from Kepler's perspective.
In May 2013, the second of Kepler's four failed the reaction-maintaining reaction wheel and ended the spaceship's primary mission. that included the continuous monitoring of 150,000 stars. (Kepler could no longer be precise enough to take the required measurements.)
But Kepler's teammates soon found a way to stabilize the observatory by sunlight pressure, and the telescope embarked on a new mission called K2. During this mission, Kepler observes various cosmic phenomena and objects, including extraterrestrial planets, during 80-day "campaigns." It has completed 18 such campaigns so far.
Kepler's current confirmed planet count stands at 2,652, with 325 of those discovered during K2. And the telescope has marked several thousand more "candidates"; most of them are likely to be confirmed after further observation or analysis, mission team members said.
Kepler refueling or other maintenance, such as astronaut spacewalks with NASA's Hubble Space Telescope, is not an option. As Hubble circles the earth, Kepler zooms around the sun, millions of miles from his home planet.