NASA TELESCOPES SEE WEATHER PATTERNS IN BROWN DWARF
WASHINGTON -- Astronomers using NASA's Spitzer and Hubble space
telescopes have probed the stormy atmosphere of a brown dwarf,
creating the most detailed "weather map" yet for this class of cool,
star-like orbs. The forecast shows wind-driven, planet-sized clouds
enshrouding these strange worlds.
Brown dwarfs form out of condensing gas, as stars do, but lack the
mass to fuse hydrogen atoms and produce energy. Instead, these
objects, which some call failed stars, are more similar to gas
planets with their complex, varied atmospheres. The new research is a
stepping stone toward a better understanding not only of brown
dwarfs, but also of the atmospheres of planets beyond our solar
system.
"With Hubble and Spitzer, we were able to look at different
atmospheric 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
at the University of Arizona in Tucson, who presented the results at
the American Astronomical Society meeting Tuesday in Long Beach,
Calif.
A study describing the results, led by Esther Buenzli, also of the
University of Arizona, is published in the Astrophysical Journal
Letters.
The researchers turned Hubble and Spitzer simultaneously toward a
brown dwarf with the long name of 2MASSJ22282889-431026. They found
that its light varied in time, brightening and dimming about every 90
minutes as the body rotated. But more surprising, the team also found
the timing of this change in brightness depended on whether they
looked using different wavelengths of infrared light.
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 atmospheric layers
because certain infrared wavelengths are blocked by vapors of water
and methane high up, while other infrared wavelengths emerge from
much deeper layers.
"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," said Mark Marley,
research scientist at NASA's Ames Research Center in Moffett Field,
Calif., and co-author of the paper. "So this large atmospheric
disturbance found by Spitzer and Hubble gives a new meaning to the
concept of extreme weather."
According to Buenzli, this is the first time researchers can probe
variability at several different altitudes at the same time in the
atmosphere of a brown dwarf. "Although brown dwarfs are cool relative
to other stars, they are actually hot by earthly standards. This
particular object is about 1,100 to 1,300 degrees Fahrenheit (600 to
700 degrees Celsius)," Buenzli said.
"What we see here is evidence for massive, organized cloud systems,
perhaps akin to giant versions of the Great Red Spot on Jupiter,"
said Adam Showman, a theorist at the University of Arizona involved
in the research. "These out-of-sync light variations provide a
fingerprint of how the brown dwarf's weather systems stack up
vertically. The data suggest regions on the brown dwarf where the
weather is cloudy and rich in silicate vapor deep in the atmosphere
coincide with balmier, drier conditions at higher altitudes -- and
vice versa."
Researchers plan to look at the atmospheres of dozens of additional
nearby brown dwarfs using both Spitzer and Hubble.
"From studies such as this we will learn much about this important
class of objects, whose mass falls between that of stars and
Jupiter-sized planets." said Glenn Wahlgren, Spitzer Program
scientist at NASA Headquarters in Washington. "This technique will
see extensive use when we are able to image individual exoplanets."
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