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Artist's concept of NASA's 1st space-based exoplanet hunter, the Kepler space telescope. Image via NASA / Wendy Stenzel / Daniel Rutter.
Astronomers only began discovering exoplanets – planets orbiting stars in other solar systems – in the 1990s, after a decades-long search. In this century, NASA's Kepler space telescope, which was specifically designed as a planet-hunter. Kepler launched into an Earth-trailing heliocentric (sun-centered) orbit in 2009. – Kepler has gone out of fuel for further science operations. NASA said this week (October 30, 2018), it has been decided to remove the spacecraft from its current, safe orbit, away from Earth.
Kepler leaves a legacy of more than 2,600 planet discoveries outside our solar system. Transiting Exoplanet Satellite Survey (TESS), launched last 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 Earth, NASA's James Webb Space Telescope.
A statement from NASA said:
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 are likely to have small, possibly rocky, planets similar in size to Earth, and located within the living area of their parent stars. That means they're located at distances from their parent stars where liquid water – a vital ingredient to life.
The most common size of planet Earth and Neptune – a world between the size of Earth and Neptune – and we have more to learn about these planets. Kepler also found nature often produces jam-packed planetary systems, in some cases with so many planets orbiting their own inner world.
Kepler's mission lasted twice as long as planned. Fuel exhaustion was seen in late June. Two weeks ago, the fuel pressure dropped to zero (the last drop).
– Chris B – NSF (@NASASpaceflight) October 30, 2018
The Kepler mission's founding principal investigator, William Borucki, now retired from NASA's Ames Research Center in California's Silicon Valley, said:
When we started designing this mission 35 years ago, we did not know a single planet outside our solar system. 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.
The Kepler space telescope launched from Earth on March 6, 2009. It was designed for an Earth-trailing heliocentric orbit, which gives the spacecraft a thermally stable environment and let it remain on a single pointing for all of the premium Kepler mission. In other words, during its prime mission, Kepler stared at a single patch of sky – with a field of view of 116 square degrees, containing approximately 150,000 stars – measuring star brightnesses within that field, and looking for minute dips in starlight that would planets in orbit around their stars.
Does the fact that Kepler found 2,600 planets around those 150,000 stars mean that we can expect only a small fraction of stars to have planets? No, and in fact the opposite is true.
In order to detect planets, Kepler had to see a remote solar system edge-on, so that the planets were passing in front of their stars from Kepler's point of view. Kepler's original 150,000 stars – which has more than 100 billion stars – is likely to have hundreds of billions of planets.
What has the @NASAKepler space telescope achieved during its time in space? Take a look at the numbers: https://t.co/Ei3m5dSdvh pic.twitter.com/zIgJw0gRSX
– NASA Kepler and K2 (@NASAKepler) October 30, 2018
Leslie Livesay, director for astronomy and physics at NASA's Jet Propulsion Laboratory, who served as Kepler project manager during mission development, said:
The Kepler mission was based on a very innovative design. It was an extremely clever approach to doing this kind of science. There were definitely challenges, but Kepler had an extremely talented team of scientists and engineers who overcame them.
Four years into the Kepler mission, after the primary mission had been met, mechanical failures only halted observations. The mission team was able to motto a fix, switching the spacecraft's field of view roughly every three months. This is an extended mission for the spacecraft, dubbed K2, which has lasted as long as the first mission and bumped Kepler's count of surveyed stars up to more than 500,000. The NASA statement said:
The observation of so many stars has allowed scientists to understand the stellar behaviors and properties, which is critical to the planets that orbit them. New research is in progress with the adventures of astronomical science, and the emergence of new technologies is expanding. The data from the extended mission were also made available to the public and the community immediately, allowing discovery 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 of data Kepler provided.
Jessie Dotson, Kepler's project scientist at NASA's Ames Research Center in California's Silicon Valley, pointed out that discoveries from Kepler are still to come:
We know the spacecraft's retirement is not the end of Kepler's discoveries. I'm excited about the various discoveries that are still coming from our data and future missions will build upon Kepler's results.
This gif shows @NASAKepler'S very final images. The end of K2 Campaign 19.
Earth-sized planets were common. It ran out of fuel while observing a nearby star known to host seven. #ThanksKepler pic.twitter.com/HMfMyv1yog – Geert Barentsen (@GeertHub) October 30, 2018
Bottom line: NASA has won the Kepler planet-hunter, after nine years in space. Much of what we know about exoplanets today comes from the Kepler mission.
Read more: Characteristics of the Kepler space telescope
Visit NASA's exoplanet archive
The 2019 lunar calendars are here! Order yours before they're gone. Makes a great gift.
Via NASA
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