20Dec2014

‘Reborn’ Kepler Spacecraft Discovers New Exoplanet

kepler-k2-exoplanet

This artist’s concept shows the first planet discovered by NASA’s Kepler spacecraft during its K2 mission, a “super Earth” called HIP 116454b. The planet has a diameter of 20,000 miles, weighs 12 times as much as Earth and orbits its star once every 9.1 days. Credit: David A. Aguilar (CfA)

Despite a malfunction that ended its primary mission in May 2013, NASA’s Kepler spacecraft has discovered a new super-Earth using data collected during its “second life,” known as the K2 mission.

University of Hawaii astronomer Christoph Baranec supplied confirming data with his Robo-AO instrument mounted on the Palomar 1.5-meter telescope, and former UH graduate student Brendan Bowler, now a Joint Center for Planetary Astronomy postdoctoral fellow at Caltech, provided additional confirming observations using the Keck II adaptive optics system on Mauna Kea.

The Kepler spacecraft detects planets by looking for planets that transit, or cross in front of, their star as seen from the vantage of Earth. During the transit, the star’s light dims slightly. The smaller the planet, the weaker the dimming, so brightness measurements must be exquisitely precise. To enable that precision, the spacecraft must maintain a steady pointing.

Kepler’s primary mission came to an end when the second of four reaction wheels used to stabilize the spacecraft failed. Without at least three functioning reaction wheels, Kepler couldn’t be pointed accurately.

Rather than giving up on the plucky spacecraft, a team of scientists and engineers developed an ingenious strategy to use pressure from sunlight as a virtual reaction wheel to help control the spacecraft. The resulting second mission promises to not only continue Kepler’s search for other worlds, but also introduce new opportunities to observe star clusters, active galaxies, and supernovae.

Artistic rendering of Kepler probe, which is now back in action discovering new exoplanets. Photo by JPL/NASA

“Like a phoenix rising from the ashes, Kepler has been reborn and is continuing to make discoveries. Even better, the planet it found is ripe for follow-up studies,” says lead author Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics (CfA).

Due to Kepler’s reduced pointing capabilities, extracting useful data requires sophisticated computer analysis. Vanderburg and his colleagues developed specialized software to correct for spacecraft movements, achieving about half the photometric precision of the original Kepler mission.

Kepler’s new life began with a nine-day test in February 2014. When Vanderburg and his colleagues analyzed that data, they found that Kepler had detected a single planetary transit.

The newfound planet, HIP 116454b, has a diameter of 20,000 miles, two and a half times the size of Earth, and weighs almost 12 times as much as Earth. This makes HIP 116454b a super-Earth, a class of planets that doesn’t exist in our solar system. The average density suggests that this planet is either a water world (composed of about three-fourths water and one-fourth rock) or a mini-Neptune with an extended, gaseous atmosphere.

NASA’s Kepler Spacecraft Baked and Ready for launch

This close-in planet circles its star once every 9.1 days at a distance of 8.4 million miles. Its host star is a type K orange dwarf slightly smaller and cooler than our Sun. The system is 180 light-years from Earth in the constellation Pisces.

During the process of verifying the discovery, Harvard astronomer and co-author John Johnson, a former postdoctoral fellow at the UH Institute for Astronomy, contacted Baranec and the Robo-AO team to obtain high-resolution imaging of HIP 116454 to determine whether it has very nearby stellar companions that could be contaminating the Kepler data, causing a misestimation of the planet’s size and other characteristics.

“Because of the flexible nature of the Robo-AO system, it was possible to add the target to the Robo-AO intelligent queue, and several observations were carried out within days of the request,” says Baranec.

While Robo-AO didn’t find any stellar companions, some additional follow-up measurements hinted that there might be a companion that is too close for Robo-AO to see. To be absolutely sure there were no contaminating companions, Bowler was asked to observe HIP 116454 with the Keck II adaptive optics system. He confirmed that HIP 116454 has no close-in stellar companions.

Since the host star is relatively bright and nearby, follow-up studies will be easier to conduct than for many Kepler planets orbiting fainter, more distant stars. “HIP 116454b will be a top target for telescopes on the ground and in space,” says Johnson.

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