"EXPLORING THE ASTEROID BELT"
Between Mars and Jupiter, hundreds of thousands of asteroids,
kilometers and
larger, form a ring around the Sun. Collisions among
asteroids and their
debris are a principal source of the interplanetary dust
cloud that gives rise
to the zodiacal light. Near-Earth asteroids originate
from the belt and offer
Earth either a threat or future resource - or both. Pieces
of them fall to
the Earth as meteorites. Asteroids are characterized
more by their diversity
than anything else. They range in composition from nickel/iron
and rock to
carbonaceous and clays. Some have been melted, some have
experienced little
thermal processing over the age of the solar system.
What are they and why
are they so different?
Asteroids are the remains of planets whose formation was
interrupted in an
embryonic stage, then shattered, mixed, and scattered.
Putting these pieces back
together is a challenge, but the promise is a picture
of conditions of the early
solar system and the processes that gave rise to Earth,
Mars, and other
terrestrial planets. Only a tiny fraction of asteroids
have been studied.
Reconstruction of these protoplanetary bodies - to the
extent possible - will
require groundbased observations of tens of thousands
of additional objects.
Fortunately, many of these are accessible to modest aperture
telescopes. A few
planetary embryos have survived unshattered - Ceres,
Vesta, and Pallas,
offering insights into early planetary formation and
evolution under different
conditions. A new Discovery mission, Dawn, will be sent
to the main asteroid
belt to rendezvous with Vesta, then Ceres, while conducting
close up studies
of many other asteroids during flybys.