"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.
Launched in 2009, the Kepler space telescope was a pioneering spacecraft that shattered most scientists' expectations.
Originally positioned to stare continuously at 150,000 stars in one star-studded patch of the sky in the constellation Cygnus, Kepler took the first survey of planets in our galaxy and became NASA's first mission to detect Earth-size planets in the habitable zones of their stars.
During its mission, Kepler found 2,681 confirmed exoplanets - the term for planets outside our solar system - and another 2,899 candidates, bringing its tally to 5,580. "Before we launched Kepler, we didn't know if planets were common or rare in our galaxy".
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, planets similar in size to Earth, and located within the habitable zone of their parent stars.
He said Kepler showed mankind how many planets might be out there.
The space agency says it has made a decision to retire Kepler while it is located in its present orbit, which it describes as safe and away from Earth.
The final commands have been sent, and the spacecraft will remain a safe distance from Earth to avoid colliding with our planet.
"Because of Kepler, we know that planets are an incredibly diverse set of objects, much more diverse than we observe in our own solar system", Hertz said.
"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 Center in California.
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.
Kepler no longer had the ability to keep itself pointed in one direction after it lost the use of two reaction wheels in 2012 and 2013. "And the Kepler mission has paved the way for future exoplanet-studying missions".
Kepler hands off the baton to TESS now, NASA said.
While Kepler was focusing on looking for planets around sun-like stars, TESS will advance its legacy by looking at smaller stars to find Earth-sized worlds out there in the universe. The probe detected distant worlds by watching for the telltale dimming of starlight as a planet passed over an alien sun's disk.
Kepler's demise was "not unexpected and this marks the end of spacecraft operations", said Paul Hertz, astrophysics division director at NASA, on a conference call with reporters.
"The Kepler spacecraft may now be retired, but the Kepler data will continue to yield scientific discoveries for years to come", Hertz said.
Six months after announcing the spacecraft's fuel stores were beginning to deplete, NASA announced Keplar's day had finally come on Wednesday. Science operations resumed in 2014, kicking off an extended mission known as K2.