Launched in 2009, the Kepler space telescope was a pioneering spacecraft that shattered most scientists' expectations. But more important, Kepler was the first NASA mission to detect Earth-size planets in the habitable zones of other stars.
Kepler's mission was to determine if earth-like planets are common or rare outside our own solar system and was originally meant to only last three-and-a-half years.
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) exoplanets similar in size to Earth.
For years, Kepler stared at a fixed area of the sky bridging the constellations Lyra and Cygnus to monitor about 150,000 stars for signs of planets.
NASA's legendary Kepler space telescope, which is responsible for the discovery of thousands of freakish and intriguing exoplanets, has officially run out of fuel. NASA has made a decision to retire the spacecraft within its current, safe orbit, away from Earth. The distinction helped scientists zero in on potential Earth-like planets and better the odds for finding life. Kepler leaves a legacy of more than 2,600 planet discoveries from outside our solar system, many of which could be promising places for life. It found inferno-like gas giants, rocky planets, planets orbiting binary stars, Earth-size planets, planets in the habitable zone capable of supporting liquid water on the surface, planets twice the size of Earth, the strangely flickering Tabby's Star, new details about the TRAPPIST-1 planets and, in December, an eight-planet system.
"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.
There was a lot of malfunction that happened with steering and dwindling hydrazine fuel levels costing $600 million spacecraft which stayed in action nearly for nine years and with 19 observation campaigns which are longer than its original four-year mission.
NASA's Kepler mission has discovered a world where two suns set over the horizon instead of just one.
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Just like biologists continue to discover new species by examining the samples already found in museum collections, the data already gathered by Kepler could keep astronomers busy for years to come.
K2 lasted as long as the first mission, allowing Kepler to survey more than 500,000 stars total.
Kepler confirmed a trove of 2,681 planets outside our solar system. It's also illuminated the tantalizing mysteries and possibilities among the stars.
"That's the path Kepler has put us on", said Paul Hertz, astrophysics division director at NASA Headquarters in Washington.
Previously, experts from NASA, which spetsializiruyutsya on the possible existence of extraterrestrial civilizations, said that aliens may be very different in appearance from the representations of the person. But the telescope has now run out of the fuel needed for further operations, leading to its retirement.
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".
Planetary exploration is going through a wider-ranging changing of the guard: For example, NASA's Dawn mission to the dwarf planet Ceres is ending, due to the same empty-tank issue that Kepler faced.