Planetesimal belts are discovered around beta Pictoris (Forwarded)

Institute of Space and Astronautical Science
Japan Aerospace Exploration Agency
Sagamihara City, Japan

2004/10/21

Planetesimal belts are discovered around beta Pictoris -- revealing an early
extrasolar planetary system

Beta Pic is a young main-sequence star with an edge-on circumstellar disk
supposed to embody an aspect of the early solar system. Its dust is considered
not to be remains from the protoplanetary disk but must be replenished by
planetesimal collisions and/or evaporation from comets, though the detailed
mechanism is still controversial. A team of astronomers from Ibaraki University,
the Japan Aerospace Exploration Agency, the University of Tokyo, and the
National Astronomical Observatory of Japan has observed the dust disk of beta
Pictoris using the Subaru telescope and an instrument called the Cooled
Mid-Infrared Camera and Spectrometer (COMICS). By analyzing the infrared dust
band emission, the team discovered that small amorphous silicate grains have
their distribution peaks around 6, 16, and 30AU (1AU=1.5x108km=the distance
between the earth and the sun). Since the small grains are blown-out very
quickly from the system due to the stellar radiation pressure on the dust, the
team concluded that the grains are replenished at ring-like locations around 6,
16, and 30AU, which are conceivable as ring-like distributions of planetesimals,
or 'planetesimal belts', like the asteroid belt in our Solar system. The
beautiful illustration shows an imaginary picture of the planetesimal belts and
the aspect that the grains are replenished by collisions between the planetesimals.

Current results have revealed inner structure of a forming planetary system by
probing the locations of grain replenishment. In particular the regions probed
by the team here correspond to the radius where planets exist in our Solar
system. Detailed structure of such inner region has been revealed for the first
time thanks to the mid-infrared high-resolution observations. The results here
have a large impact on the study of planetary system formation. Perhaps, our
Solar system has shown a similar aspect and frequent collisions of planetesimals
have occurred at its young age, too. The results here have been published as a
paper in Nature in October 2004.

Reference:
Okamoto, Y. K. et al. Nature, Vol. 431, pp.660-663 (2004)

IMAGE:
[http://www.isas.jaxa.jp/e/snews/2004/image/press_q.jpg (18KB)]
Illustration: Kouji KANBA