NASA’s elite planet-hunting spacecraft has been declared dead, just a few months shy of its 10th anniversary. Officials announced the Kepler Space Telescope’s demise Tuesday.

CAPE CANAVERAL, Fla. — NASA’s elite planet-hunting spacecraft has been declared dead, just a few months shy of its 10th anniversary.

Already well past its expected lifetime, the 9 1/2-year-old Kepler had been running low on fuel for months. Its ability to point at distant stars and identify possible alien worlds worsened dramatically at the beginning of October, but flight controllers still managed to retrieve its latest observations. The telescope has now gone silent, its fuel tank empty.

“Kepler opened the gate for mankind’s exploration of the cosmos,” said retired NASA scientist William Borucki, who led the original Kepler science team.

Kepler discovered 2,681 planets outside our solar system and even more potential candidates. It showed us rocky worlds the size of Earth that, like Earth, might harbor life. It also unveiled incredible super Earths: planets bigger than Earth but smaller than Neptune.

NASA’s astrophysics director Paul Hertz estimated that anywhere from two to a dozen of the planets discovered by Kepler are rocky and Earth-sized in the so-called Goldilocks zone. But Kepler’s overall planet census showed that 20 to 50 percent of the stars visible in the night sky could have planets like ours in the habitable zone for life, he said.

The $700 million mission even helped to uncover last year a solar system with eight planets, just like ours.

“It has revolutionized our understanding of our place in the cosmos,” Hertz said. “Now we know because of the Kepler Space Telescope and its science mission that planets are more common than stars in our galaxy.”

Almost 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.

“It was like trying to detect a flea crawling across a car headlight when the car was 100 miles away,” said Borucki said.

The resurrected mission became known as K2 and yielded 350 confirmed exoplanets, or planets orbiting other stars, on top of what the telescope had already uncovered since its March 7, 2009, launch from Cape Canaveral.

In all, close to 4,000 exoplanets have been confirmed over the past two decades, two-thirds of them thanks to Kepler.

Kepler focused on stars thousands of light-years away and, according to NASA, showed that statistically there’s at least one planet around every star in our Milky Way Galaxy.

Borucki, who dreamed up the mission decades ago, said one of his favorite 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.”

A successor to Kepler launched in April, NASA’s Tess spacecraft, has its sights on stars closer to home. It’s already identified some possible planets.

Kepler showed us that “we live in a galaxy that’s teeming with planets, and we’re ready to take the next step to explore those planets,” she said.

Another longtime spacecraft chasing strange worlds in our own solar system, meanwhile, is also close to death.

NASA’s 11-year-old Dawn spacecraft is pretty much out of fuel after orbiting the asteroid Vesta as well as the dwarf planet Ceres. It remains in orbit around Ceres, which, like Vesta, is in the asteroid belt between Mars and Jupiter.

Two of NASA’s older telescopes have been hit with equipment trouble recently, but have recovered. The 28-year-old Hubble Space Telescope resumed science observations last weekend, following a three-week shutdown. The 19-year-old Chandra X-ray Telescope’s pointing system also ran into trouble briefly in October. Both cases involved critical gyroscopes, needed to point the telescopes.

Hertz said all the spacecraft problems were “completely independent” and coincidental in timing.

Now 94 million miles from Earth, Kepler should remain in a safe, stable orbit around the sun. Flight controllers will disable the spacecraft’s transmitters, before bidding a final “good night.”</s>The US space agency's Kepler space telescope has run out of fuel and is being retired after nine and a half years, having helped discover more than 2,600 planets, some of which may hold life, officials said Tuesday.

The unmanned space telescope, which launched in 2009, revealed that billions of hidden planets are in space and revolutionized humanity's understanding of the universe, experts said.

Kepler helped astronomers measure potential planets by glimpsing transits, or moments when planets passed in front of their stars.

Kepler showed 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," NASA said in a statement.

"That means they're located at distances from their parent stars where liquid water -- a vital ingredient to life as we know it -- might pool on the planet surface."

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.

Signals that fuel was nearly out were seen two weeks ago.

Scientists were able to get all the data from Kepler down to Earth before it completely ran dry.

NASA said it has decided to retire the spacecraft "within its current, safe orbit, away from Earth."

NASA's retired principal investigator for the Kepler mission, Bill Borucki, described it as an "enormous success."

"We have shown that there are more planets than stars in our galaxy," Borucki said.

NASA has experienced a series of spacecraft problems lately.

NASA's Opportunity rover is stalled on the surface of Mars following a major dust storm that struck in late May and June.

The asteroid-hopping Dawn mission ran out of fuel last month.

The Hubble Space Telescope and Chandra X-Ray Observatory experienced technical problems earlier this month that have since been fully repaired.

NASA says Kepler's mission may be over but its discoveries will be studied for years to come.

The next-generation planet hunter space telescope for NASA, TESS, launched in April and will survey far more cosmic terrain than Kepler.

Both use the same system of detecting planetary transits, or shadows cast as they pass in front of their star.

The new spacecraft will focus on nearby exoplanets, those in the range of 30 to 300 light-years away.

Kepler confirmed a trove of 2,681 planets outside our solar system. However most of these exoplanets were too distant and dim to be examined further.

The far more advanced James Webb Space Telescope, scheduled to lift off in 2021, should be able to reveal more about planets' mass, density and the makeup of their atmosphere -- all clues to habitability.

"Because of Kepler, what we think about our place in the universe has changed," said Hertz.

"The Kepler mission has paved the way for future exoplanet studying missions."</s>The time has come to say good night to NASA’s revolutionary Kepler space telescope.

For nearly a decade, the intrepid planet-hunter has peered deep into the sky to reveal a universe teeming with previously unknown worlds around distant stars.

By discovering more than 2,600 confirmed planets, Kepler launched a new era of exploration and redefined humanity’s place in the cosmos, said Paul Hertz, director of NASA’s astrophysics division in Washington, D.C.

But now the spacecraft is out of fuel.

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NASA officials will send the final commands to turn off its transmitter and disable its default protections within the next week, they announced Tuesday.

Then Kepler will drift into an eternal sleep in a safe orbit around the sun, trailing the Earth at a distance of 94 million miles.

“We collected every last bit of science data, and in the end, we didn’t have a drop of fuel left over for anything else,” said Charlie Sobeck, the Kepler mission’s former project manager and chief engineer at NASA’s Ames Research Center in Mountain View, Calif.

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Before Kepler launched in 2009, nobody knew whether planets like the ones in our solar system were common or rare in the cosmos.

The telescope’s steady, persistent gaze revealed that there are more planets than stars in our galaxy.

In addition, data collected by Kepler suggest that 20% to 50% of those stars should have at least one Earth-sized planet at the right distance from its star to allow water to pool on its surface. Scientists believe this is a prerequisite for life as we know it.

Kepler also showed astronomers that the universe is made up of a great diversity of planets, including many that have no counterpart in our solar system, said Jessie Dotson, the Kepler project scientist at Ames Research Center.

Among the menagerie, Kepler found small planets orbiting their stars so quickly that rocks would melt, and gas giants so much bigger than Jupiter that they would rival small stars.

The telescope also discovered a new class of previously unknown planets: super-Earths, which are bigger than our planet but smaller than Neptune.

Among some of its more unusual finds was Kepler-16b, which orbits a binary star system. If you were to stand on the surface of this planet, you would see two suns in the sky.

Kepler-22b is a world blanketed by a liquid ocean. Kepler-444 is an ancient solar system that hosts five rocky planets formed 2 billion years before our own.

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“It’s almost like imagination is not the limit at all,” Dotson said.

(NASA)

Scientists and engineers consider the mission a huge success, but it was not without its share of obstacles.

The telescope launched on March 6, 2009, with an initial mission that was scheduled to last 3½ years. Its first assignment was to focus on about 150,000 stars clustered in the constellation Cygnus.

Kepler detected potential planets by watching for minuscule dips in starlight that result when a planet passes in front of its parent star.

“It’s like trying to detect a flea crawling in front of a car headlight, when the car is 100 miles away,” said William Borucki, the architect of the Kepler mission who retired three years ago.

To achieve this level of precise observation, the telescope had to remain extremely still, which it did with the help of four reaction wheels.

One of those wheels failed in 2012, but the remaining three were enough to prevent Kepler from wobbling. Then a second wheel failed in 2013, threatening to bring the mission to an end.

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That prospect brought some scientists to tears.

Then engineers came up with a clever fix, using pressure from tiny particles of sunlight to help hold the spacecraft in place. With this virtual third wheel, Kepler was back in business for a new mission, dubbed K2.

In a nine-day engineering test to see whether the new positioning method would work, the telescope spotted a super-Earth that was 2½ times wider than Earth with about 12 times as much mass.

“I thought of it as the little spacecraft that could,” Dotson said. “It always did everything we asked of it, and sometimes more.”

In its second life, Kepler shifted its position every few months. It examined a variety of targets that included proto-stars, galaxy clusters and supernovae.

By the time the K2 mission ended, Kepler had surveyed more than half a million stars, NASA said.

Mission engineers knew that Kepler wouldn’t function forever. The space telescope relies on fuel-powered thrusters to turn it toward Earth to downlink data, and that fuel would one day run out.

Sobeck said his team started watching the fuel carefully over the summer when they got the first indications that it might be running low.

By mid-September they realized the spacecraft could no longer point with its customary precision.

By mid-October, it was running on fumes.

But even as the Kepler mission comes to a close, NASA’s next planet-hunting space telescope is already scouring the skies for planets around 200,000 nearby stars.

The Transiting Exoplanet Survey Satellite, or TESS, launched in April and is focused on finding stars just 300 light-years away, or about 10 times closer than most of the stars surveyed by Kepler.

Scientists have started analyzing the first sets of data that TESS has sent down and are already finding promising planet candidates, said Padi Boyd, a TESS project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

Future missions, including the James Webb Space Telescope, will further investigate these planets to see whether there are any indications of life.

But Kepler will always have the distinction of being the first space telescope to prove that planets are abundant in the universe.

Sobeck said that as a kid watching “Star Trek,” he had no problem believing that there were planets of all kinds in the cosmos. Even so, Kepler’s evidence that they exist hit him like a sledgehammer to the chest.

“There is a big difference between believing a thing and knowing it,” he said.

deborah.netburn@latimes.com

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UPDATES:

7:32 p.m.: This article has been updated with additional information throughout.

2:10 p.m. This article has been updated with additional comments from scientists and information about the K2 mission.

1:20 p.m. This article has been updated with comments from scientists and additional information about the Kepler mission.

This article was originally published at 12:25 p.m.</s>The American space agency announced on Tuesday the machine has run out of fuel and will be unable to perform further missions. As a result, the agency will be abandoning the spacecraft where it lies, in a heliocentric orbit.But what does that mean for the telescope? Will it come crashing down on Earth? Will it aim for the Sun? Or will it spin forever into oblivion?NASA’s Ames Research Center punched in the numbers to see what would happen to the telescope in the foreseeable future. Because, after all, there are only so many human-made objects in heliocentric orbit.First off, it’s important to know that Kepler does not spin in orbit close to Earth, but rather at 94 million miles away. It also doesn’t spin around Earth, but around the Sun, just like all other planets do.This pretty much means it’s impossible for the telescope to come crashing down to Earth, or into the Sun, for that matter. Instead, it will spin in a pattern that will bring it inside and outside of Earth’s orbit possibly forever.NASA calculates that Kepler, because it travels on a larger, thus slower orbit than Earth, will almost be caught by by the blue planet sometimes around the year 2060. Such a huge rock coming near the telescope will change its orbit to one closer to the Sun, thus faster.This means Kepler will move faster than the Earth, but only until for a century or so, as when it approaches Earth once more, the planet will kick it back to the previous, slower orbit.And this dance could go on forever, as seen in the video attached below.As it dances its sinusoidal dance with Earth, Kepler leaves behind a wealth of knowledge: over 2,600 planets discovered during its nine-year mission, “many of which could be promising places for life.”</s>NASA is saying “goodnight” to its pioneering Kepler telescope, which a few months shy of its 10th birthday but years past its expected lifespan, has finally run out of fuel.

The planet-hunting spacecraft, credited with discovering thousands of exoplanets, or planets beyond our solar system, will be retired and left in its current orbit, a safe distance from Earth, NASA announced Tuesday. Kepler’s transmitter and other instruments will be shut down in the coming days.

Kepler was launched in March 2009 with enough fuel to keep it going for at least six years, according to The Verge. It far surpassed expectations, however, collecting data in deep space for more than nine years. In all, the telescope made more than 2,600 exoplanet discoveries, NASA said.

“As NASA’s first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond,” Thomas Zurbuchen, associate administrator of NASA’s science mission directorate, said in a statement. “Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.”

Kepler searched for alien worlds by looking out for their transits, which are dips in the brightness of stars that could indicate orbiting planets.

“It was like trying to detect a flea crawling across a car headlight when the car was 100 miles away,” William Borucki, who led the original Kepler science team, told AP of the telescope’s technology,

When Kepler’s stabilizing equipment began malfunctioning in 2013, NASA feared it was doomed. But the mission team managed to salvage the telescope after figuring out how to use the pressure of sunlight to balance the spacecraft. Once the fix was made, NASA approved a new mission for the spacecraft, dubbed K2.

Kepler continued to hunt for planets during its K2 phase. As Space.com notes, the spacecraft also studied “a variety of cosmic objects and phenomena, from comets and asteroids in our own solar system to faraway supernova explosions.”

“TESS builds on Kepler’s foundation with fresh batches of data in its search of planets orbiting some 200,000 of the brightest and nearest stars to the Earth, worlds that can later be explored for signs of life,” NASA said.</s>NASA is saying "goodnight" to its pioneering Kepler telescope, which a few

NASA is saying “goodnight” to its pioneering Kepler telescope, which a few months shy of its 10th birthday but years past its expected lifespan, has finally run out of fuel.

The planet-hunting spacecraft, credited with discovering thousands of exoplanets, or planets beyond our solar system, will be retired and left in its current orbit, a safe distance from Earth, NASA announced Tuesday. Kepler’s transmitter and other instruments will be shut down in the coming days.

Kepler was launched in March 2009 with enough fuel to keep it going for at least six years, according to The Verge. It far surpassed expectations, however, collecting data in deep space for more than nine years. In all, the telescope made more than 2,600 exoplanet discoveries, NASA said.

“As NASA’s first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond,” Thomas Zurbuchen, associate administrator of NASA’s science mission directorate, said in a statement. “Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.”

Kepler searched for alien worlds by looking out for their transits, which are dips in the brightness of stars that could indicate orbiting planets.

“It was like trying to detect a flea crawling across a car headlight when the car was 100 miles away,” William Borucki, who led the original Kepler science team, told AP of the telescope’s technology,

When Kepler’s stabilizing equipment began malfunctioning in 2013, NASA feared it was doomed. But the mission team managed to salvage the telescope after figuring out how to use the pressure of sunlight to balance the spacecraft. Once the fix was made, NASA approved a new mission for the spacecraft, dubbed K2.

Kepler continued to hunt for planets during its K2 phase. As Space.com notes, the spacecraft also studied “a variety of cosmic objects and phenomena, from comets and asteroids in our own solar system to faraway supernova explosions.”

In April, a spacecraft successor to Kepler ― NASA’s Transiting Exoplanet Survey Satellite, or TESS ― was launched.

“TESS builds on Kepler’s foundation with fresh batches of data in its search of planets orbiting some 200,000 of the brightest and nearest stars to the Earth, worlds that can later be explored for signs of life,” NASA said.

Calling Kepler’s mission “stunningly successful,” TESS project scientist Padi Boyd told AP that the retired telescope has shown us that “we live in a galaxy that’s teeming with planets.”

Boyd also noted that our exploration of the cosmos has only just begun.

“We’re ready to take the next step to explore those planets,” Boyd said.</s>NASA’s planet-hunting Kepler spacecraft has died in orbit after a historic nine-year mission that first opened our eyes to the existence of planets beyond our solar system.

The space agency revealed the grim news in a teleconference this afternoon after the veteran craft put itself into ‘sleep mode’ earlier this month.

The aging telescope was expected to run out of fuel sometime in the near future – but, exactly when this would happen was unclear.

Now, after weeks of uncertainty, NASA confirmed Kepler has officially run out of the fuel it would need to continue science operations.

According to NASA, the now-retired spacecraft is in a 'safe orbit, away from Earth.'

Kepler, which launched back in 2009, came to be known by its team as 'the little spacecraft that could,' going above and beyond the expectations NASA had for it.

It was the first spacecraft to survey the planets in our own galaxy, and over the years its observations confirmed the existence of more than 2,600 exoplanets - many of which could be key targets in the search for alien life.

Before Kepler, we'd never found any planets outside of our solar system.

'As NASA's first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond,' said Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate in Washington.

'Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm,' Zurbuchen said.

'Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.'

The Kepler data indicated that there were far more planets in the sky than we'd ever imagined. According to NASA, we now know there are more planets than stars.

Kepler successfully transmitted data from its final observation campaign back to Earth at the beginning of October. All of this is now in the archive and publicly available, the Kepler team says.

During this so-called Deep Space Network time, however, when Kepler was pointed toward Earth to beam its data home, the team learned that the spacecraft had transitioned to its no-fuel-use sleep mode.

At the time, the team said it is assessing the cause and 'evaluating possible next steps.'

But following their investigation, the team concluded it was time to officially retire the craft.

During its long-running mission, however, the team says Kepler was 'stunningly successful.

Kepler showed us that 'we live in a galaxy that's teeming with planets, and we're ready to take the next step to explore those planets,' said Padi Boyd, a scientist with the upcoming TESS mission, which will serve as Kepler's successor.

'It has revolutionized our understanding of our place in the cosmos,' NASA's astrophysics director Paul Hertz said.

'Now we know because of the Kepler Space Telescope and its science mission that planets are more common than stars in our galaxy.'

The Kepler mission ran into complications four years after it launched, when mechanical failures temporarily halted its work.

At the time, the spacecraft had already completed its primary mission objectives.

The team ultimately managed to salvage Kepler by switching its field of view roughly every three months, allowing it to move on to an extended mission dubbed K2.

The spacecraft continued to search for possible orbiting planets, looking for dips in brightness as a planet transits its star.

'It was like trying to detect a flea crawling across a car headlight when the car was 100 miles away,' said retired NASA scientist William Boruki, who led the original Kepler science team.

Kepler completed 18 missions after embarking on its K2 phase.

NASA says it ‘pushed Kepler to its full potential’ before its demise, with multiple observation campaigns and thousands of planet discoveries.

The space agency will use the data from Campaign 19 – Kepler’s final observations – to complement that collected by its Transiting Exoplanet Survey Satellite (TESS) mission, which launched this past April.

And, given the bountiful data Kepler has collected over the years, the team says there’s still much more to learn in the spacecraft’s legacy.

'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’s Silicon Valley.

'I'm excited about the diverse discoveries that are yet to come from our data and how future missions will build upon Kepler's results.'</s>“NASA’s Kepler space telescope has run out of fuel needed for further science operations,” the agency said in a press release. “NASA has decided to retire the spacecraft within its current safe orbit away from Earth.”

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, NASA said. Kepler surveyed more than half a million stars during its active operations, the agency added.

“Now that we know planets are everywhere, Kepler has set us on a new course that is full of promise for future generations to explore our galaxy,” Kepler mission founding principal investigator William Borucki said in the release.

READ MORE: NASA's Parker Solar Probe Breaks Record for Closest and Fastest Approach to Sun

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, NASA said in the release.

Kepler is being retired into a safe orbit 94 million miles away from the Earth, after being the agency's first mission to successfully find Earth-size planets orbiting within the habitable zones of their stars NASA said.</s>The tally of potentially habitable alien planets may have to be revised downward a bit.

To date, NASA's prolific Kepler space telescope has discovered about 30 roughly Earth-size exoplanets in their host stars' "habitable zone" — the range of orbital distances at which liquid water can likely exist on a world's surface.

Or so researchers had thought. New observations by the European Space Agency's (ESA) Gaia spacecraft suggest that the actual number is probably significantly smaller — perhaps between two and 12, NASA officials said Oct. 26. [ Photos: Gaia Spacecraft to Map Milky Way Galaxy ]

Gaia launched in December of 2013 to create an ultraprecise 3D map of the Milky Way. So far, this map includes position information for about 1.7 billion stars and distance data for about 1.3 billion stars, according to NASA officials.

Gaia's observations suggest that some of the Kepler host stars are brighter and bigger than previously believed, the officials added. Planets orbiting such stars are therefore likely larger and hotter than previously thought.

The "hotter" issue is straightforward: A larger, brighter star pumps out more heat. The "larger" correlation stems from Kepler's planet-hunting strategy, which is called the "transit method."

Kepler notices the tiny brightness dips caused when a planet crosses its parent star's face from the telescope's perspective. Estimates of such planets' sizes are derived from the percentage of the stellar disk they block during these "transits." So, if the stars' diameter is revised upward, so is that of the planet.

"The whole issue has always been, how well do we understand the star?" Eric Mamajek, deputy program chief scientist for NASA's Exoplanet Exploration Program, said in a statement. "This is just another chapter of that ongoing story."

The new results shouldn't discourage folks hoping that Earth life isn't alone in the galaxy; there's still a lot of potentially habitable real estate in the Milky Way, NASA officials stressed. But the Gaia data reinforce that astronomers, astrobiologists and planetary scientists still have a lot to learn about exoplanet habitability.

"We're still trying to figure out how big a planet can be and still be rocky," Jessie Dotson, an astrophysicist at NASA's Ames Research Center in Silicon Valley, said in the same statement. Dotson is the project scientist for Kepler's current, extended mission, which is known as K2.

And then there's the concept of the habitable zone. Basing habitability solely on orbital distance ignores important planetary characteristics, such as mass, which influences a world's ability to hold onto an atmosphere. Then, there's atmospheric composition, which greatly affects a planet's temperature.

Also, who's to say that life requires liquid water on the surface? A number of frozen-over moons outside our own solar system's habitable zone, such as Jupiter's Europa and Saturn's Enceladus, have buried oceans that may be capable of supporting life as we know it. (And we haven't even gotten into the possibility of life as we don't know it, which may depend on something other than water as a solvent.)

The $600 million Kepler mission launched in March 2009. During Kepler's four-year primary mission, the telescope stared at about 150,000 stars simultaneously, watching for planetary transits. This work ended in May 2013, when the second of Kepler's four orientation-maintaining reaction wheels failed.

In 2014, Kepler began K2, during which the craft observes a variety of cosmic objects and phenomena over shifting 80-day "campaigns." Some of these campaigns involve planet hunting; indeed, 354 of the spacecraft's 2,681 confirmed alien-world discoveries to date have come during K2.

Kepler's total tally represents about 70 percent of the roughly 3,800 known exoplanets. And the Kepler count will continue to grow; nearly 3,000 planet "candidates" await confirmation by follow-up analysis or observation, and history suggests that most of these will end up being the real deal.

But Kepler's observing days are drawing to a close. The spacecraft is extremely low on fuel and recently went into a "no fuel-use" sleep mode.

Mike Wall's book about the search for alien life, " Out There ," will be published on Nov. 13 by Grand Central Publishing. Follow him on Twitter @michaeldwall . Follow us @Spacedotcom or Facebook . Originally published on Space.com .</s>NASA's Kepler Space Telescope, which launched in 2009 and revolutionized our vision of the galaxy and the universe over the past decade, is now permanently retired and out of service.

The space agency first saw signs Kepler was running out of gas earlier this year and last week the telescope went into a low-fuel sleep mode. NASA said Tuesday that the spacecraft won't be waking up.

"Science operations are over," NASA astrophysics division director Paul Hertz told reporters on a conference call.

He noted that Kepler was able to confirm scientists' suspicions that space is filled with planets similar to Earth. Kepler's catalog of confirmed planets beyond our solar system includes over 2,600 worlds and dozens that could potentially support alien life. While the telescope is done collecting new data, Hertz says astronomers are still working with what's been collected over the years.

"Kepler data will continue to yield scientific discoveries for years to come."

When the spacecraft's "low fuel light" came on earlier this year, the Kepler team began to take measures to ensure that all remaining data could be recovered and downloaded before it went dark for good.

"In the end we didn't have a drop of fuel leftover for anything else," said Kepler project system engineer Charlie Sobeck.

Kepler had already been operating on borrowed time for years after one of the craft's reaction wheels, which help it point at its target stars, began to fail in 2012. Engineers came up with a way to use pressure from sunlight itself to stabilize and point Kepler, and the new adapted mission, dubbed K2, went on to discover more planets for another half decade.

"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, in a news release. "Now that we know planets are everywhere, Kepler has set us on a new course that's full of promise for future generations to explore our galaxy."

One of Kepler's successors is currently in space and searching for new planets. NASA's Transiting Exoplanet Survey Satellite has already spotted its first pair of Earth-like planets and will continue to catalog dozens more. The hope is that the upcoming James Webb Space Telescope (a supersize, 21st century follow-up to Hubble) will be able to take a much closer look and perhaps even look for signs of life on the worlds that TESS and Kepler have pointed us toward.

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NASA announces that the Kepler spacecraft has expended all its fuel and will be retired after nearly 10 years of service, having found more than 2,600 exoplanets.