Canadian astronomers detect water in exoplanet’s atmosphere

This artist's impression shows three of HR 8799 four planets. (Image credit: Gemini Observatory)A group of Canadian and American astronomers studying a nearby star system have found both water vapour and carbon monoxide in the atmosphere of one of the planets there.

HR 8799 is a young, bright star about 129 light years away from us, in the constellation Pegasus, and so far, astronomers have discovered four Jupiter-sized planets orbiting around it. Unlike planets found around many other stars, where astronomers only know they're there due to indirect evidence (measuring transits or detecting a wobble in the star), HR 8799 is close enough to us, and the planets are big enough and orbit far enough away from their star, that astronomers are able to see them in pictures taken of the star system.

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Since they can see the planets so clearly, they can separate out the light that each planet emits (large planets like Saturn and Jupiter not only reflect light from their star, but also emit their own light from processes inside the planet). Taking a high-resolution spectrum of one of these planets — HR 8799 c, a gas giant planet roughly 7 times more massive than Jupiter, that orbits its star at roughly the same distance that Pluto orbits our Sun — the researchers found evidence for water vapour and carbon monoxide in the planet's atmosphere.

Astronomers have discovered water in the atmosphere of a massive exoplanet 129 light years …"We have been able to observe this planet in unprecedented detail because of Keck Observatory's advanced instrumentation, our ground-breaking observing and data processing techniques, and because of the nature of the planetary system," said Quinn Konopacky, according to Space Daily. Konopacky is an astronomer with the Dunlap Institute for Astronomy and Astrophysics, University of Toronto and lead author of the study.

Astronomers have discovered water in the atmosphere of a massive exoplanet 129 light years away. (Image credit: …"This is the sharpest spectrum ever obtained of an extrasolar planet," said co-author Bruce Macintosh, an astronomer at the Lawrence Livermore National Laboratory, in California, according to Space Daily. "This shows the power of directly imaging a planetary system-the exquisite resolution afforded by these new observations has allowed us to really begin to probe planet formation."

"With this level of detail," says Travis Barman, another co-author who is an astronomer at the Lowell Observatory in Flagstaff, AZ, according to Space Daily, "we can compare the amount of carbon to the amount of oxygen present in the atmosphere, and this chemical mix provides clues as to how the planetary system formed."

There are two prevailing models on how gas giant planets form. In the first, called 'core accretion', the planets slowly form in their star's disk of debris, building up a solid core that gradually accumulates gases from the disk over time. The second, called 'gravitational instability', involves planets forming nearly instantly due to parts of the disk collapsing in on themselves. The model of 'core accretion' is the more widely accepted version, but examining the atmospheres of the planets offers a way to test the two models.

If the planets formed by the 'gravitational instability' model, they would expect them to show similar compositions to their star. However, according to the researchers' findings, the amount of oxygen (in the water) and carbon (in the carbon monoxide) detected in HR 8799 c shows a different ratio than what the planet's star has. This showed that the planet formed via the 'core accretion' model.

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"Once the solid cores grew large enough, their gravity quickly attracted surrounding gas to become the massive planets we see today," said Konopacky, according to Space Daily. "Since that gas had lost some of its oxygen, the planet ends up with less oxygen and less water than if it had formed through a gravitational instability."

"We can directly image the planets around HR 8799 because they are all large, young, and very far from their parent star. This makes the system an excellent laboratory for studying exoplanet atmospheres," said co-author Christian Marois, an astronomer with the National Research Council of Canada, who works at Dominion Astrophysical Observatory, in Victoria, BC, according to Space Daily.

"Since its discovery, this system just keeps on surprising us."

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