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Scientists Peer Into a Brown Dwarf, Find Stormy Atmosphere

Scientists Peer Into a Brown Dwarf, Find Stormy Atmosphere

By Daniel Stolte/UANews and Whitney Clavin/JPL - January 8, 2013

A University of Arizona-led team of astronomers for the first time has used NASA's Spitzer and Hubble space telescopes simultaneously to peer into the stormy atmosphere of a brown dwarf, creating the most detailed "weather map" yet for this class of strange, not-quite-star-and-not-quite-planet objects. The forecast shows wind-driven, planet-sized clouds enshrouding these strange worlds.

Brown dwarfs form out of condensing gas like stars but fail to accrue enough mass to ignite the nuclear fusion process necessary to turn them into a star. Instead, they pass their lives as dimly glowing, constantly cooling gas balls similar to gas planets with their complex, varied atmospheres. The new research is a stepping stone toward better understanding not only brown dwarfs but also the atmospheres of planets beyond our solar system.

"With Hubble and Spitzer, we were able to look at the layers of a brown dwarf, similar to the way doctors use medical imaging techniques to study the different tissues in your body, said Daniel Apai, the principal investigator of the research from the UA, who presented the results at the American Astronomical Society meeting in Long Beach, Calif. Apai is an assistant professor with joint appointments in the UA's departments of astronomy and planetary sciences.

A study describing the results, led by Esther Buenzli, a postdoctoral researcher in the UA's department of astronomy, is published in the Astrophysical Journal Letters.

The researchers turned Hubble and Spitzer simultaneously toward a brown dwarf called 2MASSJ22282889-431026. They found that its light varied in time, brightening and dimming as the body rotated around every 1.4 hours. But more surprising, the team also found that the timing of this brightening changed depending on whether they looked at it with Spitzer or Hubble using different wavelengths of infrared light (Hubble sees shorter-wavelength infrared light than Spitzer).

These variations are the result of different layers, or patches, of material swirling around the brown dwarf in windy storms as large as Earth itself. Spitzer and Hubble see different atmosphere layers because certain infrared wavelengths are blocked by vapors of water and methane high up, while other infrared wavelengths emerge from much deeper.

"What we see here is evidence for massive, organized cloud systems, perhaps akin to giant versions of the Great Red Spot on Jupiter or large-scale storm systems on Earth," said Adam Showman, a theorist with the UA's Lunar and Planetary Laboratory who was involved in the research.

"We were expecting the phases of the light variations to be in sync between the two telescopes, so we were really surprised that they were offset," said Buenzli. "This is the first time that we can probe variability at several different altitudes at the same time in the atmosphere of a brown dwarf."

"The deeper layers appear to lag behind the higher layers," Apai explained. "This tells us that the same or similar cloud distribution is present in the different layers, but the deeper you look, the later you will see the same clouds turning into view."

"We were very surprised to see such a big lag. Our best guess is this has to do with the brown dwarf's atmospheric circulation. The bigger picture here is that we see a very large-scale atmospheric structure in this brown dwarf."

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