Free Astronomy Magazine March-April 2015

SPACE CHRONICLES outermost planet orbits on the edge of the so-called “habitable zone,” where the temperature may be just right for liquid water, be- lieved necessary to support life, on the planet’s surface. “The compositions of these new- found planets are unknown, but, there is a very real possibility the outer planet is rocky like Earth,” said Erik Petigura, a University of California, Berkeley graduate stu- dent who spent a year visiting the UH Institute for Astronomy. “If so, this planet could have the right temperature to support liquid wa- ter oceans.” The planets were con- firmed by the NASA Infrared Tele- scope Facility (IRTF) and the W. M. Keck Observatory in Hawaii as well as telescopes in California and Chile. “Keck's contribution to this discov- ery was vital,” said Andrew How- ard, a University of Hawaii astron- omer on the team. “The adaptive optics image from NIRC2 showed the star hosting these three planets is a single star, not a binary. It show- ed that the planets are real and not an artifact of some masquerading multi-star system.” Due to the competitive state of plan- et finding, and the fact that time on the twin Keck telescopes are scheduled months in advance, the team asked UC Berkeley Astrono- mer, Imke de Pater to gather some data during her scheduled run. “The collegiality of the Keck Obser- vatory community is just wonder- ful,” Howard said. “Imke took time away from her own science obser- vations to get us images of this sys- tem, all on a couple hours’ notice.” The new discovery paves the way for studies of the atmosphere of a warm planet nearly the size of Earth. “We’ve learned in the past year that planets the size and tempera- ture of Earth are common in our Milky Way galaxy,” Howard said. “We also discovered some Earth- size planets that appear to be made of the same materials as our Earth, mostly rock and iron.” The astronomers next hope to de- termine what elements are in the planets’ atmospheres. If these warm, nearly Earth-size planets have thick, hydrogen-rich atmospheres, there is not much chance for life. “A thin atmosphere made of nitro- gen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many extrasolar planets discovered by the Kepler Mission are enveloped by thick, hydrogen- rich atmospheres that are probably incompatible with life as we know it,” said Ian Crossfield, the Univer- sity of Arizona astronomer who led the study. The discovery is all the more remarkable because Kepler is now hobbled by the loss of two re- action wheels that kept it pointing at a fixed spot in space. Kepler, launched in 2009, was re- born in 2014 as “K2” with a clever strategy of pointing the telescope in the plane of the Earth’s orbit to stabilize the spacecraft. Kepler is back to mining the cosmos for plan- ets by searching for eclipses, or transits, as planets orbit in front of their host stars and periodically block some of the starlight. “I was devastated when Kepler was crip- pled by a hardware failure,” Peti- gura added. “It’s a testament to the ingenuity of NASA engineers and scientists that Kepler can still do great science.” Kepler sees only a small fraction of the planetary systems in its gaze, those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are simply missed by Kepler. “It’s re- markable that the Kepler telescope is now pointed in the ecliptic, the plane that Earth sweeps out as it orbits the Sun,” UH graduate stu- dent Benjamin Fulton explains. “This means that some of the planets discovered by K2 will have orbits lined up with Earth’s, a celes- tial coincidence that allows Kepler to see the alien planets, and Kep- ler-like telescopes in those very planetary systems (if there are any) to discover Earth.” “Here’s looking at you, looking at me,” said Howard. In addition to Howard, Petigura, and Fulton, UH graduate student Kimberly Aller, and UH astronomer Michael Liu were among the two dozen scientists who contributed to the study. T his whimsical car- toon shows the three newly discov- ered extrasolar plan- ets (right) casting shadows on their host star that can been seen as eclipses, or transits, at Earth (left). Earth can be detected by the same effect, but only in the plane of Earth's orbit (the ecliptic). During the K2 mis- sion, many of the ex- trasolar planets dis- covered by the Kep- ler telescope will have this lucky dou- ble cosmic alignment that would allow for mutual discovery—if there is anyone on those planets to dis- cover Earth. The three new planets or- biting EPIC 201367065 are just out of align- ment; while they are visible from Earth, our solar system is tilted just out of their view. [W. M. Keck Observatory] n