Image: This graph shows the brightness variations of the brown dwarf named 2MASSJ22282889-431026 measured simultaneously by both NASA’s Hubble and Spitzer space telescopes. As the object rotates every 1.4 hours, its emitted light periodically brightens and dims. Surprisingly, the timing, or phase, of the variations in brightness changes when measured at different wavelengths of infrared light. Spitzer and Hubble’s wavelengths probe different layers in the atmosphere of the brown dwarf. The phase shifts indicate complex clouds or weather patterns that change with altitude. Credit: NASA/JPL-Caltech.

Probing a Brown Dwarf’s Atmosphere

by PAUL GILSTER on JANUARY 9, 2013

The American Astronomical Society’s meeting in Long Beach is going to occupy us for several days, and not always with exoplanet news. Brown dwarfs, those other recent entrants into the gallery of research targets, continue to make waves as we learn more about their nature and distribution. The hope of finding a brown dwarf closer than Alpha Centauri has faded and recent work has emphasized that there may be fewer of these objects than thought — WISE data point to one brown dwarf for every six stars. But habitable planets around brown dwarfs are not inconceivable, and in any case we are continuing to build the census of nearby objects.

The latest from AAS offers up what could be considered a probe of brown dwarf ‘weather.’ If the idea of weather on a star seems odd, consider that the cooler brown dwarfs are far closer to gas giants than stars, unable to trigger hydrogen fusion and gradually cooling as they age. That means cloud patterns form and huge storms plow through the various atmospheric layers. At AAS, Daniel Apai (University of Arizona) presented the results of work on the brown dwarf 2MASSJ22282889-431026, which he conducted with a team led by the university’s Esther Buenzli. The results are useful not just for brown dwarf study but planetary atmospheres as well.

Using the Hubble and Spitzer space telescopes simultaneously, the researchers found that every ninety minutes the light from the star varied as it rotated. Because they were looking at the object at different wavelengths, they were able to see that the timing of the brightness change depended on wavelength. Some infrared wavelengths emerge from deep within the star, while others are blocked by water vapor and methane at higher altitudes. What we’re getting, in other words, is a look at layers of material being carried around the brown dwarf in likely storms.

But these aren’t your usual clouds, according to Mark Marley (NASA Ames), a co-author on the paper:

“Unlike the water clouds of Earth or the ammonia clouds of Jupiter, clouds on brown dwarfs are composed of hot grains of sand, liquid drops of iron, and other exotic compounds. So this large atmospheric disturbance found by Spitzer and Hubble gives a new meaning to the concept of extreme weather.”

Read more: Probing a Brown Dwarf’s Atmosphere — Centauri Dreams.

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