Kepler proves it can still find planets

This artist's conception portrays the first planet discovered by the Kepler spacecraft during its K2 mission. A transit of the planet was teased out of K2's noisier data using ingenious computer algorithms developed by a CfA researcher. The newfound planet, HIP 116454b, has a diameter of 20,000 miles (two and a half times the size of Earth) and weighs 12 times as much. It orbits its star once every 9.1 days.

To paraphrase Mark Twain, the report of the Kepler spacecraft's death was greatly exaggerated. Despite a malfunction that ended its primary mission in May 2013, Kepler is still alive and working. The evidence comes from the discovery of a new super-Earth using data collected during Kepler's "second life."

"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).

NASA's Kepler spacecraft detects planets by looking for transits, when a star dims slightly as a planet crosses in front of it. 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, K2, promises to not only continue Kepler's search for other worlds, but also introduce new opportunities to observe star clusters, active galaxies, and supernovae.

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 9-day test in February 2014. When Vanderburg and his colleagues analyzed that data, they found that Kepler had detected a single planetary transit.

They confirmed the discovery with radial velocity measurements from the HARPS-North spectrograph on the Telescopio Nazionale Galileo in the Canary Islands. Additional transits were weakly detected by the Microvariability and Oscillations of STars (MOST) satellite.

The newfound planet, HIP 116454b, has a diameter of 20,000 miles, two and a half times the size of Earth. HARPS-N showed that it 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.

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.

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 Harvard astronomer and co-author John Johnson of the CfA.

The research paper reporting this discovery has been accepted for publication in The Astrophysical Journal.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

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Is an understanding of dark matter around the corner? Experimentalists unsure

Scientists have long known that dark matter is out there, silently orchestrating the universe's movement and structure. But what exactly is dark matter made of? And what does a dark matter particle look like? That remains a mystery, with experiment after experiment coming up empty handed in the quest to detect these elusive particles.

With some luck, that may be about to change. With ten times the sensitivity of previous detectors, three recently funded dark matter experiments have scientists crossing their fingers that they may finally glimpse these long-sought particles. In recent conversations with The Kavli Foundation, scientists working on these new experiments expressed hope that they would catch dark matter, but also agreed that, in the end, their success or failure is up to nature to decide.

"Nature is being coy," said Enectali Figueroa-Feliciano, an associate professor of physics at the MIT Kavli Institute for Astrophysics and Space Research who works on one of the three new experiments. "There's something we just don't understand about the internal structure of how the universe works. When theorists write down all the ways dark matter might interact with our particles, they find, for the simplest models, that we should have seen it already. So even though we haven't found it yet, there's a message there, one that we're trying to decode now."

The first of the new experiments, called the Axion Dark Matter eXperiment, searches for a theoretical type of dark matter particle called the axion. ADMX seeks evidence of this extremely lightweight particle converting into a photon in the experiment's high magnetic field. By slowly varying the magnetic field, the detector hunts for one axion mass at a time.

"We've demonstrated that we have the tools necessary to see axions," said Gray Rybka, research assistant professor of physics at the University of Washington who co-leads the ADMX Gen 2 experiment. "With Gen2, we're buying a very, very powerful refrigerator that will arrive very shortly. Once it arrives, we'll be able to scan very, very quickly and we feel we'll have a much better chance of finding axions -- if they're out there."

The two other new experiments look for a different type of theoretical dark matter called the WIMP. Short for Weakly Interacting Massive Particle, the WIMP interacts with our world very weakly and very rarely. The Large Underground Xenon, or LUX, experiment, which began in 2009, is now getting an upgrade to increase its sensitivity to heavier WIMPs. Meanwhile, the Super Cryogenic Dark Matter Search collaboration, which has looked for the signal of a lightweight WIMP barreling through its detector since 2013, is in the process of finalizing the design for a new experiment to be located in Canada.

"In a way it's like looking for gold," said Figueroa-Feliciano, a member of the SuperCDMS experiment. "Harry has his pan and he's looking for gold in a deep pond, and we're looking in a slightly shallower pond, and Gray's a little upstream, looking in his own spot. We don't know who's going to find gold because we don't know where it is."

Rybka agreed, but added the more optimistic perspective that it's also possible that all three experiments will find dark matter. "There's nothing that would require dark matter to be made of just one type of particle except us hoping that it's that simple," he said. "Dark matter could be one-third axions, one-third heavy WIMPs and one-third light WIMPs. That would be perfectly allowable from everything we've seen."

Yet the nugget of gold for which all three experiments search is a very valuable one. And even though the search is difficult, all three scientists agreed that it's worthwhile because glimpsing dark matter would reveal insight into a large portion of the universe.

"We're all looking and somewhere, maybe even now, there's a little bit of data that will cause someone to have an 'Ah ha!' moment," said Harry Nelson, professor of physics at the University of California, Santa Barbara and science lead for the LUX upgrade, called LUX-ZEPLIN. "This idea that there's something out there that we can't sense yet is one of those things that sends chills down my spine."

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