WASHINGTON: Newly discovered three-planet system holds clues to atmospheres of Earth-size worlds. 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 Hawaii 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.”
“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 graduate students Benjamin Fulton and Kimberly Aller, and UH astronomer Michael Liu are among the two dozen scientists who contributed to the study. The planets were confirmed by the NASA Infrared Telescope Facility (IRTF) and Keck Observatory in Hawaii 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 discovery is all the more remarkable because Kepler is now hobbled by the loss of two reaction wheels that kept it pointing at a fixed spot in space. Kepler, launched in 2009, was reborn in 2014 as
