NASA announced on Tuesday that the Kepler mission - which has transformed how we understand planets outside of our solar system - is officially over.
After nine years in deep space collecting data that indicate our sky to be filled with billions of hidden planets - more planets even than stars - NASA's Kepler space telescope has run out of fuel needed for further science operations.
The space agency says it has chose to retire Kepler while it is located in its present orbit, which it describes as safe and away from Earth.
Kepler opened our eyes to the variety of worlds beyond our solar system, with its discovery of more than 2,600 planets orbiting other stars. After completing its initial mission, NASA tasked Kepler with its extended K2 mission, which resulted in the spacecraft having surveyed more than half a million stars.
"I've always been interested in astronomy", William Borucki, retired Kepler principal investigator said. When scientists factored those finds into statistical formulas that take Kepler's limitations into account, they concluded that 20 to 50 percent of the Milky Way's stars may have rocky planets in habitable zones.
The most common size of planet Kepler found doesn't exist in our solar system, however.
Nearly lost in 2013 because of equipment failure, Kepler was salvaged by engineers and kept peering into the cosmos, thick with stars and galaxies, ever on the lookout for dips in in the brightness of stars that could indicate an orbiting planet.
Kepler was launched atop its United Launch Alliance Delta II (7925-10L) rocket from Cape Canaveral Air Force Station's Space Launch Complex 17B on March 7, 2009.
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Engineers managed to downlink all the final science data stored aboard the spacecraft before control was lost.
In a briefing with reporters, agency officials said that Kepler ended operations after exhausting the last of its hydrazine fuel used for attitude control.
A replacement: Several exoplanet-hunting missions are in the works, including the James Webb Space Telescope, now due to launch in 2021 after a series of delays.
Kepler was succeeded by NASA's Transiting Exoplanet Survey Satellite, or TESS, which was launched in April. By fixating on a specific area of the sky in the constellation Cygnus, Kepler was able to continuously monitor the varying brightnesses of roughly 150,000 stars. Kepler also found Mother Nature often produces jam-packed planetary systems with an astounding number of planets orbiting close to their parent stars that our own inner Solar System looks sparse by comparison.
The $700 million mission even helped to uncover previous year a solar system with eight planets, just like ours. "Kepler has had a successful nine-and-a-half year mission".
"We saw it drop from 90 psi [pounds per square inch] all the way down to 25 psi" over a few hours, said Charlie Sobeck, project system engineer for Kepler at NASA's Ames Research Center.
"Now, because of Kepler, what we think about the universe has changed", NASA astrophysics division director Paul Hertz told the Verge. Scientists are expected to spend a decade or more in search of new discoveries in the treasure trove of data Kepler provided. "I'm excited about the diverse discoveries that are yet to come".
"Kepler kind of just cracked that out of being the typical expectation", Boyd said during the news conference.