Kepler Mission Ends after Paradigm Changing Discovery of Thousands of Planets

This illustration depicts NASA's exoplanet hunter, the Kepler space telescope. The agency announced on Oct. 30, 2018, that Kepler has run out of fuel and is being retired within its current and safe orbit, away from Earth. Kepler leaves a legacy of more than 2,600 exoplanet discoveries.  Credits: NASA/Wendy Stenzel

Ken Kremer  --   SpaceUpClose.com  --   31 October 2018

CAPE CANAVERAL, FL –  NASA’s paradigm changing Kepler exoplanet hunting mission has come to an illustrious end after discovering thousands of new planets beyond our  solar system – a finding that completely changed our concept on our place in the Universe and that continued until completely exhausting all of its fuel reserves just days ago.

Kepler has been retired by NASA and the planet hunting touch has been passed to recently launched TESS. 

Before the mission began in 2009 we did not know the frequency of planets in our Galaxy compared to stars – or whether they were common or extraordinary.

NASA announced the retirement of Kepler at a media briefing Tuesday, October 30, saying that not a drop of fuel was left to point the spacecraft and send any more science data. 

The revolutionary $692 million Kepler mission lasted more than twice as long as originally planned since it was launched in 2009. 

"Kepler revolutionized our understanding of our place in the cosmos," said Paul Hertz, director of astrophysics at NASA Headquarters at the Oct. 30 media briefing.

"Before we launched Kepler, we didn't know if planets were common or rare in our galaxy," he said. "We didn’t know much about planets. But now we know there are more planets than stars in our galaxy. Planets are more common than stars. 

“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. And because of Kepler, we know that solar systems come in a variety of configurations unlike our own. Solar systems with Jupiters orbiting their stars in only a few days, solar systems with small, rocky planets packed inside the orbit of Mercury, so close that the planets are in resonance with each other."

And it discovered a new class of planets unknown in our solar system that vary in size between Earth and Neptune – and that they are actually among the most common type of planet. 

"One of the common kinds of planets that Kepler detected are planets that are larger than Earth and smaller than Neptune, a type of planet that doesn't exist in our own solar system.”

“But Kepler’s mission is now ended and we are handing off the hunt for Exoplanets to NASA’s recently launched TESS.” 

Artist's conception of NASA’s Kepler Space Telescope.  Credits: NASA

"The Kepler mission has been an enormous success," said the Kepler mission's founding principal investigator, William Borucki, at the briefing, and now retired from NASA’s Ames Research Center in California’s Silicon Valley. He conceived the mission 35 years ago and finally won approval from NASA in 2001 on his 5^th try!

"We have shown there are more planets than stars in our galaxy, that many of these planets are roughly the size of the Earth and some, like the Earth, are at the right distance from their star that there could be liquid water on the surface, a situation conducive to the existence of life."

But Kepler started running low on fuel in June. So the team knew the end was near and quickly downloaded all the science data so that nothing would be left behind on the spacecraft and lost to humanity.

“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 announced.

“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.”

Kepler By The Numbers - Mission Statistics. NASA’s Kepler space telescope is done with its work collecting astounding science data showing there are more planets than stars in our galaxy. Here’s a round-up of what Kepler has achieved.  Credit: NASA/Ames/Wendy Stenzel

To date Kepler’s observations have confirmed the existence of 2,681 new planets orbiting other stars. There are another 2,899 planet candidates awaiting confirmation pending observations from ground and space-based telescopes.

"When we started conceiving this mission 35 years ago we didn't know of a single planet outside our solar system," said Borucki.

"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."

"Now we know there are billions of planets that are rocky like the Earth and are orbiting their stars in the habitable zone, or the Goldilocks zone, where their temperatures might be conducive to water on the surface."

How many of those Kepler planets are Earth-like and Earth-sized? - I asked at the briefing. What have the ground-based and space-based telescope told us about those planets?

Hertz replied that “that was a great question ! Because there is no consensus yet.”

“Until recently we thought between about a dozen and 30.” 

“But new data from the GAIA probe has forced us to rethink the distance of these planets to the host stars. It seems now these stars may be brighter, hence the planets are bigger," Hertz told me..

“Therefore now we think now there are between 2 and 12 Earth like worlds that could potentially support life.”

“But there is no definitive list.”

Kepler uses the transit method of discovering planets – looking for a very slight dimming of 1/10,000 of a star’s brightness as a planet moved in front from a distance of 100 miles.

“Kepler using the transit method “is like trying to detect a fly crawling across a car headlight when the car was 100 miles away. And the instrument must do it for 150,000 stars simultaneously,” Borucki explained.

Launched on a United Launch Alliance Delta II rocket 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.”

Before retiring the spacecraft, scientists pushed Kepler to its full potential, said NASA

“Kepler successfully completed 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.”

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

"Because of fuel exhaustion, the Kepler spacecraft has reached the end of its service life," he explained

"While this may be a sad event, we're by no means unhappy with the performance of this marvelous machine. Kepler's nine-and-a-half-year flight was more than twice the original target."

Watch for Ken’s continuing onsite coverage of NASA, SpaceX, ULA, Boeing, Lockheed Martin, Northrop Grumman and more space and mission reports direct from the Kennedy Space Center, Cape Canaveral Air Force Station, Florida and Wallops Flight Facility, Virginia.

Stay tuned here for Ken's continuing Earth and Planetary science and human spaceflight news: www.kenkremer.com –www.spaceupclose.com – twitter @ken_kremer – email: ken at kenkremer.com

Dr. Kremer is a research scientist and journalist based in the KSC area.

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