Despite a malfunctioning steering system and dwindling hydrazine fuel levels, the $600 million spacecraft stayed in action for nine years and 19 observation campaigns-far longer than its original four-year mission.
"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. Kepler was created to survey more than 100,000 stars in our galaxy to determine the number of sun-like stars that have Earth-size and larger planets, including those that lie in a star's 'habitable zone, ' a region where liquid water, and perhaps life, could exist.
The next-generation planet hunter space telescope for Nasa, TESS, launched in April and will survey far more cosmic terrain than Kepler. Professor Lewis Dartnell from the University Of Westminster discusses Kepler's legacy. But the innovative spacecraft enjoyed an illustrious career, discovering as many as 2,600 planets and inspiring new fields of research, NASA said.
Mission scientists anxious that the spacecraft may have been irreparably rendered ineffective after the steering malfunction in 2012, though they eventually came up with an ingenious solution in 2013 using pressure generated by the sun's rays to compensate for a failed reaction wheel and aim it at observation targets.
NASA scientists are expected to spend the next decade trawling through data provided by Kepler in search of new discoveries. When it launched in 2009, it was equipped with "the largest digital camera outfitted for outer space observations at that time", NASA wrote, and scientists on Earth had very limited knowledge of planets beyond the reach of the solar system.
The telescope's findings indicate that distant star systems are populated with billions of planets, and it even helped pinpoint the first moon known outside our solar system.
Tess will mainly scout for planets in the Goldilocks zone of a star. The spacecraft had been in what NASA called a "no-fuel-use" safe mode since it was contacted by controllers October 19.
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.
"When we started conceiving this mission 35 years ago, we didn't know of a single planet outside our solar system", said the Kepler mission's founding principal investigator, William Borucki, now retired.
The most common size of planet Kepler found doesn't exist in our solar system - a world between the size of Earth and Neptune - and we have much to learn about these planets.
Now orbiting the sun 94 million miles (156 million km) from Earth, the spacecraft will drift further from our planet when mission engineers turn off its radio transmitters, the U.S. space agency said.
"We know the spacecraft's retirement isn't the end of Kepler's discoveries", according to Jessie Dotson, Kepler's project scientist at the Ames Research Center.
Engineers managed to downlink all the final science data stored aboard the spacecraft before control was lost.
Both use the same system of detecting planetary transits, or shadows cast as they pass in front of their star.
"Because of Kepler, what we think about our place in the universe has changed", Hertz said.
"The Kepler mission has paved the way for future exoplanet studying missions".