NASA's Spitzer Telescope Sees Signs of Alien Asteroid Belt
NASA's Spitzer Space Telescope has spotted what may be the dusty
spray of asteroids banging together in a belt that orbits a star
like our Sun.
NASA's Spitzer Space Telescope has spotted what may be the dusty
spray of asteroids banging together in a belt that orbits a star
like our Sun. The discovery offers astronomers a rare glimpse at
a distant star system that resembles our home, and may represent
a significant step toward learning if and where other Earths
form."Asteroids are the leftover building blocks of rocky planets like
Earth," said Dr. Charles Beichman of the California Institute of
Technology, Pasadena, Calif. Beichman is lead author of a paper
that will appear in the Astrophysical Journal. "We can't directly
see other terrestrial planets, but now we can study their dusty
fossils."Asteroid belts are the junkyards of planetary systems. They are
littered with the rocky scraps of failed planets, which
occasionally crash into each other, kicking up plumes of dust. In
our own solar system, asteroids have collided with Earth, the
moon and other planets.If confirmed, the new asteroid belt would be the first detected
around a star about the same age and size as our Sun. The star,
called HD69830, is located 41 light-years away from Earth. There
are two other known distant asteroid belts, but they circle
younger, more massive stars.While this new belt is the closest known match to our own, it is
not a perfect twin. It is thicker than our asteroid belt, with 25
times as much material. If our solar system had a belt this
dense, its dust would light up the night skies as a brilliant
band.The alien belt is also much closer to its star. Our asteroid belt
lies between the orbits of Mars and Jupiter, whereas this one is
located inside an orbit equivalent to that of Venus.Yet, the two belts may have one important trait in common. In our
solar system, Jupiter acts as an outer wall to the asteroid belt,
shepherding its debris into a series of bands. Similarly, an
unseen planet the size of Saturn or smaller may be marshalling
this star's rubble.One of NASA's future planet-hunting missions, SIM PlanetQuest,
may ultimately identify such a planet orbiting HD 69830.  The
mission, which will detect planets as small as a few Earth
masses, is scheduled to launch in 2011.Beichman and colleagues used Spitzer's infrared spectrograph to
observe 85 Sun-like stars. Only HD 69830 was found to possibly
host an asteroid belt. They did not see the asteroids themselves,
but detected a thick disk of warm dust confined to the inner
portion of the star system. The dust most likely came from an
asteroid belt in which dusty smash-ups occur relatively
frequently, about every 1,000 years."Because this belt has more asteroids than ours, collisions are
larger and more frequent, which is why Spitzer could detect the
belt," said Dr. George Rieke, University of Arizona, Tucson, co-
author of the paper. "Our present-day solar system is a quieter
place, with impacts of the scale that killed the dinosaurs
occurring only every 100 million years or so."To confirm that the dust detected by Spitzer is indeed ground-up
asteroids, a second less-likely theory will have to be ruled out.
According to the astronomers, it is possible a giant comet,
almost as big as Pluto, got knocked into the inner solar system
and is slowly boiling away, leaving a trail of dust. This
hypothesis came about when the astronomers discovered the dust
around the star consists of small silicate crystals like those
found in comet Hale-Bopp. One of these crystals is the bright
green-colored gem called forsterite."The 'super comet' theory is more of a long shot," Beichman said,
"but we'll know soon enough." Future observations of the star
using Spitzer and ground-based telescopes are expected to
conclude whether asteroids or comets are the source of the dust.Other authors of this study include G. Bryden, T. Gautier, K.
Stapelfeldt and M. Werner of NASA's Jet Propulsion Laboratory,
Pasadena, Calif.; and K. Misselt, J. Stansberry and D. Trilling
of the University of Arizona.The Jet Propulsion Laboratory 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. Caltech
manages JPL for NASA. Spitzer's infrared spectrograph was built
by Cornell University, Ithaca, N.Y. Its development was led by
Dr. Jim Houck of Cornell.For artist's concepts and more information, visit:www.spitzer.caltech.edu/spitzer.