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Exoplanet atmosphere offers clues about far-off planet's formation

March 14, 2013|By Eryn Brown
  • An artist's depiction of the planetary system of the star HR 8799. Researchers reported details about planetary atmospheres in the system this week.
An artist's depiction of the planetary system of the star HR 8799.… (Dunlap Institute for Astronomy…)

Astronomers have had great success using tools like NASA’s Kepler space telescope to peer into the heavens and find planets outside our solar system, but they haven’t yet been able to describe those worlds in great depth. In large part, that is because they usually detect so-called exoplanets through indirect means — by observing how they obscure a tiny bit of light as they pass between their star and our vantage point, or how their gravity makes their host star wobble. 

Scientists can surmise a planet’s distance from its star and some details about its size and mass, but it’s difficult for them, for instance, to characterize the components in an exoplanet atmosphere — the kind of detail that might help researchers assess, someday, whether life could thrive on a planet or not. 

But on Thursday, a team of Canadian and American scientists reported new observations that provide unprecedented detail about a large, gaseous planet orbiting a young, bright star called HR 8799, about 130 light years away from our sun. The observations, made using at the Keck Observatory in Hawaii, were published online in the journal Science.

Pointing the telescope toward the far-off planetary system and analyzing infrared signals, the team could see “chemical fingerprints” of the atmosphere of the giant planet HR 8799c that potentially explain how it formed, the study’s coauthors said Wednesday during a phone call with reporters.

Because the planet’s atmosphere has a higher amount of carbon relative to oxygen than its host star does, the scientists believe that water vapor coalesced to form its core, attracting gas to make an atmosphere, said study first author Quinn Konopacky, who investigates star and planet formation at the University of Toronto.

She said that the observations could help planetary scientists understand the origins of the familiar planets in Earth’s nearby neighborhood. 

“This is like a scaled-up version of our solar system. There are four gas giants, something like an asteroid belt and something like an Oort cloud. Maybe there could be planets more like the Earth interior to the planets we see now,” she said, adding that it was “interesting to speculate.”

Separately, another team of researchers announced a different set of observations of the 8799 planetary system, made using a new technique to analyze images from Caltech’s Palomar Observatory. That team, led by American Museum of Natural History astronomer Ben R. Oppenheimer and including researchers from Caltech, analyzed the atmospheres of all four of the gas giants orbiting HR 8799 simultaneously, a first for any planetary system, according to a Caltech statement. 

During the press call, Science study co-author Bruce Macintosh, of the Lawrence Livermore National Laboratory in California, said that the Palomar results complemented his team’s findings, which were more narrowly focused but provided a more detailed view of HR 8799c’s chemical makeup.

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