Free Astronomy Magazine July-August 2015

SPACE CHRONICLES much more quickly because APF is a dedicated facility that robotical- ly searches for planets every clear night. Training computers to run the observatory all night, without hu- man oversight, took years of effort by the University of California Ob- servatories staff and graduate stu- dents on the discovery team. “We initially used APF like a regular telescope, staying up all night search- ing star to star. But the idea of lett- ing a computer take the graveyard shift was more appealing after months of little sleep. So we wrote software to replace ourselves with a robot,” said University of Hawaii graduate student BJ Fulton. The Kepler Space Telescope has dis- covered thousands of extrasolar planets and demonstrated that they are common in our Milky Way galaxy. However, nearly all of these planets are far from our solar sys- tem. Most nearby stars have not been thoroughly searched for the small “super-Earth” planets (larger than Earth but smaller than Nep- tune) that Kepler found in great abundance. This discovery shows the type of planetary system that astronomers expect to find around many nearby stars in the com- ing years. “The three planets are unlike anything in our solar sys- tem, with masses 7-8 times the mass of Earth and orbits that take them very close to their host star,” explains UC Berke- ley graduate stu- dent LaurenWeiss. “This level of au- tomation is a game-changer in astronomy,” How- ard said. “It’s a bit like owning a driverless car that goes planet shop- ping.” Observations by APF, APT, and Keck Observatory helped verify the plan- ets and rule out other explanations. “Starspots, like sunspots on the sun, can momentarily mimic the signa- tures of small planets. Repeated ob- servations over many years allowed us to separate the starspot signals from the signatures of these new planets,” said Evan Sinukoff, a UH graduate student who contributed to the discovery. The robotic observations of HD 7924 are the start of a systematic survey for super-Earth planets orbiting nearby stars. Fulton will lead this two- year search with the APF as part of his research for his doctoral disserta- tion. “When the survey is complete we will have a census of small planets orbiting sun-like stars within approximately 100 light-years of Earth,” Fulton said. Telescope automation is relatively new to astron- omy, and UH astronomers are build- ing two forefront facilities. Christoph Baranec built the Robo- AO observatory to takes high-reso- lution images using a laser to re- move the blur of Earth’s atmo- sphere, and John Tonry is develop- ing ATLAS, a robotic observatory that will hunt for killer asteroids. In honor of the donations of Gloria and Ken Levy that helped facilitate the construction of the Levy spec- trograph on APF and supported Lauren Weiss, the team has infor- mally named the HD 7924 system the “Levy Planetary System.” The team also acknowledges the support of NASA, the U.S. Naval Observatory, and the University of California for its support of Lick Ob- servatory. A rtist’s impression of a view from the HD 7924 planetary system looking back toward our sun, which would be easily visible to the naked eye. Since HD 7924 is in our northern sky, an observer looking back at the sun would see ob- jects like the Southern Cross and the Magellanic Clouds close to our sun in their sky. [Art by Karen Te- ramura & BJ Fulton, UH IfA] n