Newly discovered three-planet system holds clues to atmospheres of earth-size worlds

January 16, 2015  |   |  Comments
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This whimsical cartoon shows the three newly discovered extrasolar planets (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 mission, many of the extrasolar planets discovered by the Kepler telescope will have this lucky double cosmic alignment that would allow for mutual discovery—if there is anyone on those planets to discover Earth. The three new planets orbiting EPIC 201367065 are just out of alignment; while they are visible from Earth, our solar system is tilted just out of their view (Image credit: K. Teramura, UH Institute for Astronomy)


Extrasolar planets are being discovered by the hundreds, but are any of these newfound worlds really like Earth? A planetary system recently discovered by the Kepler spacecraft will help resolve this question.

The system of three planets, each just larger than Earth, orbits a nearby star called EPIC 201367065. The three planets are 1.5–2 times the size of Earth, and the outermost planet orbits on the edge of the so-called “habitable zone,” where the temperature may be just right for liquid water, believed necessary to support life, on the planet’s surface.

“We’ve learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy,” explains University of Hawaiʻi at Mānoa astronomer Andrew Howard. “We also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron.”

The compositions of these newfound planets are unknown. “There is a very real possibility that the outer planet is rocky like Earth,” noted Erik Petigura, a University of California, Berkeley graduate student who spent a year visiting the UH Institute for Astronomy. “If so, this planet could have the right temperature to support liquid water oceans.”

In addition to Howard and Petigura, UH Mānoa graduate students Benjamin Fulton and Kimberly Aller, and UH Mānoa astronomer Michael Liu are among the two dozen scientists who contributed to the study. The confirmed planets were by the NASA Infrared Telescope Facility and Keck Observatory in Hawaiʻi as well as telescopes in California and Chile.

The new discovery paves the way for studies of the atmosphere of a warm planet nearly the size of Earth. The three new planets are particularly favorable for atmospheric studies because they orbit a nearby, bright star. Next, the team of astronomers that made the discovery hopes to observe the planets with the Hubble Space Telescope and other observatories to determine what elements are in the planets’ atmospheres. If Hubble finds that these warm, nearly Earth-size planets have thick, hydrogen-rich atmospheres, they will learn that there is not much chance for life.

“A thin atmosphere made of nitrogen 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,” says Ian Crossfield, the University of Arizona astronomer who led this study.

The paper presenting this work, “A Nearby M Star with Three Transiting Super-Earths Discovered by K2,” has been submitted to The Astrophysical Journal and is available for free here.

For the full story, read the Institute for Astronomy news release.

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Category: Research


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