Credit: NASA/JPL-Caltech/T.Pyle (IPAC)
Swirling, stormy clouds may be ever-present on cool celestial orbs
called brown dwarfs. New observations from NASA's Spitzer Space
Telescope suggest that most brown dwarfs are roiling with one or more
planet-size storms akin to Jupiter's "Great Red Spot."
"As the
brown dwarfs spin on their axis, the alternation of what we think are
cloud-free and cloudy regions produces a periodic brightness variation
that we can observe," said Stanimir Metchev of the University of Western
Ontario, Canada. "These are signs of patchiness in the cloud cover."
Metchev
is principal investigator of the brown dwarf research. The results were
presented at a news conference today at the 223rd annual meeting of the
American Astronomical Society in Washington by Metchev's colleague,
Aren Heinze, of Stony Brook University, New York.
Brown dwarfs
form as stars do, but lack the mass to fuse atoms continually and
blossom into full-fledged stars. They are, in some ways, the massive kin
to Jupiter.
Scientists think that the cloudy regions on brown
dwarfs take the form of torrential storms, accompanied by winds and,
possibly, lightning more violent than that at Jupiter or any other
planet in our solar system. However, the brown dwarfs studied so far are
too hot for water rain; instead, astronomers believe the rain in these
storms, like the clouds themselves, is made of hot sand, molten iron or
salts.
In a Spitzer program named "Weather on Other Worlds,"
astronomers used the infrared space telescope to watch 44 brown dwarfs
as they rotated on their axis for up to 20 hours. Previous results had
suggested that some brown dwarfs have turbulent weather, so the
scientists had expected to see a small fraction vary in brightness over
time. However, to their surprise, half of the brown dwarfs showed the
variations. When you take into account that half of the objects would be
oriented in such a way that their storms would be either hidden or
always in view and unchanging, the results indicate that most, if not
all, brown dwarfs are racked by storms.
"We needed Spitzer to do
this," said Metchev. "Spitzer is in space, above the thermal glow of the
Earth's atmosphere, and it has the sensitivity required to see
variations in the brown dwarfs' brightness."
The results led to
another surprise as well. Some of the brown dwarfs rotated much more
slowly than any previously measured, a finding that could not have been
possible without Spitzer's long, uninterrupted observations from space.
Astronomers had thought that brown dwarfs sped up to very fast rotations
when they formed and contracted, and that this rotation didn't wind
down with age.
"We don't yet know why these particular brown
dwarfs spin so slowly, but several interesting possibilities exist,"
said Heinze. "A brown dwarf that rotates slowly may have formed in an
unusual way -- or it may even have been slowed down by the gravity of a
yet-undiscovered planet in a close orbit around it."
The work may
lead to a better understanding of not just brown dwarfs but their
"little brothers": the gas-giant planets. Researchers say that studying
the weather on brown dwarfs will open new windows onto weather on
planets outside our solar system, which are harder to study under the
glare of their stars. Brown dwarfs are weather laboratories for planets,
and, according to the new results, those laboratories are everywhere.
Other
researchers on the team include: Daniel Apai and Davin Flateau of the
University of Arizona, Tucson; Mark Marley of NASA Ames Research Center,
Moffett Field; Jacqueline Radigan of the Space Telescope Science
Institute, Baltimore, Md.; Etienne Artigau of Universite de Montreal,
Canada; Adam Burgasser of University of California San Diego; Peter
Plavchan of NASA's Exoplanet Science Institute at the California
Institute of Technology, Pasadena; and Bertrand Goldman of Max-Planck
Institute for Astronomy, Germany.
NASA's Jet Propulsion
Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science
operations are conducted at the Spitzer Science Center at the California
Institute of Technology in Pasadena. Spacecraft operations are based at
Lockheed Martin Space Systems Company, Littleton, Colorado. Data are
archived at the Infrared Science Archive housed at the Infrared
Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.
Source: Spitzer Space Telescope
