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.
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.
Tess project scientist Padi Boyd called Kepler's mission "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," 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."
NASA Retires Kepler Space Telescope, Passes Planet-Hunting Torch
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. 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.
"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. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.”
Kepler has opened our eyes to the diversity of planets that exist 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. 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.
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. 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.
"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 from NASA’s Ames Research Center in California’s Silicon Valley. "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."
Launched on March 6, 2009, the Kepler space telescope combined cutting-edge techniques in measuring stellar brightness with the largest digital camera outfitted for outer space observations at that time. 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 the agency's first mission to detect Earth-size planets in the habitable zones of their stars.
"The Kepler mission was based on a very innovative design. It was an extremely clever approach to doing this kind of science," said Leslie Livesay, director for astronomy and physics at NASA’s Jet Propulsion Laboratory, who served as Kepler project manager during mission development. "There were definitely challenges, but Kepler had an extremely talented team of scientists and engineers who overcame them.”
Four years into the mission, after the primary mission objectives had been met, mechanical failures temporarily halted observations. The mission team was able to devise a fix, switching the spacecraft’s field of view roughly every three months. This enabled an extended mission for the spacecraft, dubbed K2, which lasted as long as the first mission and bumped Kepler's count of surveyed stars up to more than 500,000.
The observation of so many stars has allowed scientists to better understand stellar behaviors and properties, which is critical information in studying the planets that orbit them. New research into stars with Kepler data also is furthering other areas of astronomy, such as the history of our Milky Way galaxy and the beginning stages of exploding stars called supernovae that are used to study how fast the universe is expanding. The data from the extended mission were also made available to the public and science community immediately, allowing discoveries to be made at an incredible pace and setting a high bar for other missions. Scientists are expected to spend a decade or more in search of new discoveries in the treasure trove of data Kepler provided.
"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."
Before retiring the spacecraft, scientists pushed Kepler to its full potential, successfully completing multiple observation campaigns and downloading valuable science data even after initial warnings of low fuel. The latest data, from Campaign 19, will complement the data from NASA’s newest planet hunter, the Transiting Exoplanet Survey Satellite, launched in April. 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 by missions, such as NASA’s James Webb Space Telescope.
NASA's Ames Research Center in California's Silicon Valley manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation in Boulder, Colorado, operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.