"But now we know, because of the Kepler Space Telescope and its science mission, that planets are more common than stars in our galaxy". "Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars", said Zurbuchen.
There two vastly different NASA spacecraft are about to run out of fuel: The Kepler spacecraft, which spent nine years in deep space collecting data that detected thousands of planets orbiting stars outside our solar system; and the Dawn spacecraft, which spent 11 years orbiting and studying the main asteroid belt's two largest objects, Vesta and Ceres.
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.
"Before we launched Kepler, we didn't know if planets were common or rare in our galaxy", he said.
Kepler helped astronomers measure potential planets by glimpsing transits, or moments when planets passed in front of their stars. Kepler also found nature often produces jam-packed planetary systems, in some cases with so many planets orbiting close to their parent stars that our own inner solar system looks sparse by comparison.
"We know the spacecraft's retirement isn't the end of Kepler's discoveries", said Jessie Dotson, Kepler's project scientist at NASA's Ames Research Centre in California's Silicon Valley.
NASA's venerable Kepler space telescope, which discovered almost 2,700 exoplanets in distant star systems, has officially been retired after finally running out of fuel, the space agency wrote in a statement on Tuesday.
Kepler was NASA's first planet-hunting mission, and it opened our eyes to the diversity of planets that exist in our galaxy and elsewhere.
Now orbiting some 156 million kilometres from Earth, the spacecraft will drift further from our planet after its retirement, the USA space agency said.
Kepler also found planets "completely unlike those in our solar system", he told reporters. During its mission, Kepler found 2,681 confirmed planets and another 2,899 candidates, bringing its tally to 5,580.More news: United Nations hails acquittal of Asia Bibi by Pakistan’s Supreme Court
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.
Several of them are rocky and Earth-sized in the so-called Goldilocks or habitable zone of a star - an orbit where temperatures are neither too cold nor too hot, but just right for the existence of water, which is considered a key ingredient for life.
Both missions were extended past their originally anticipated lifetime because of the innovative work of their engineers and scientists.
"He put together a like-minded team of scientists and engineers", Hertz said of Borucki.
Four years into the mission, after the primary mission objectives had been met, mechanical failures temporarily halted observations.
Mr Borucki described his favourite exoplanet, named Kepler 22B, which was first spotted by the telescope in 2009 and is located more than 600 light years from Earth.
Since that time, NASA changed the craft's mission to adjust to the telescope's new normal, calling the updated mission K2.
Kepler hands off the baton to TESS now, NASA said.