The Asteroid Belt is the region of interplanetary space
between Mars and Jupiter where most asteroids are found. It contains irregularly
shaped chunks of debris called asteroids.
The Space Asteroids are made of rock and metal, mostly nickel and iron. Contrary
to popular imagery, the asteroid belt is mostly empty.
Facts about the Asteroid Belt
The main asteroid belt extends from 255 to 600 million km (2.15 to 3.3
astronomical units) from the Sun and may contain over a million objects bigger
than 1 km across.
* Diameter: The largest objects are Ceres (1,003 km), Pallas (608 km) and
Vesta (538 km).
* Total Mass: The total mass
of all the asteroids is less than that of the Moon. There are 26 known asteroids
larger than 200 km across.
* Location: The Asteroid Belt is a region between the inner planets and outer planets where
thousands of asteroids are found orbiting around the Sun.
How big are the
asteroids? Ceres is the largest asteroid in the asteroid belt and
is the only dwarf planet in the belt. Pallas is second largest and
the second asteroid to have been discovered. More than half the
mass of the main belt is contained in the four largest objects:
Ceres, Vesta, Pallas and Hygiea.
The current main belt
consists primarily of three categories of asteroids: C-type
(carbonaceous asteroids), S-type (silicate asteroids) and M-type
detected water-ice and carbon-based organic compounds on the
surface of asteroid Themis. The discovery of water ice on 24
Themis was announced in April 2010. Two teams of researchers
independently verified that the asteroid 24 Themis is coated in a
layer of frost. This discovery has changed scientists perspectives
The discovery may also
be a boon to NASA's new space exploration program which is aiming
to send astronauts to visit a near-Earth asteroid in the future.
Scientists believe the
asteroids are the pieces of a planet that never formed. One
possible theory is the ongoing gravitational tug-of-war between
Jupiter and Mars has prevented the pieces from bonding together,
hence, this planet was never created.
The first flybys of asteroids were performed in 1991 and
1993 by NASA's Galileo spacecraft and in 1996 by the Near Earth Asteroid
Rendezvous (NEAR) spacecraft.
In the 1980's, the Soviet Union was planning to send a
probe to Vesta. No information available on its status.
is on a 3-billion-km (1.7-billion-mile) journey to the asteroid belt to orbit
asteroid Vesta and dwarf planet Ceres. Scientists hope to study the conditions
of the solar system's earliest days.
More Facts on the Asteroid Belt
- Did you know?
Other regions of small solar system bodies include the
Centaurs, the Kuiper belt and scattered disk and the Oort cloud.
Beyond the orbit of Neptune lies an even large and more populous region of minor
bodies known as the Kuiper belt.
When was the Asteroid Belt Discovered?
The process of discovering the asteroid belt began in the
late 1700s. The first asteroid was discovered in 1801 by Italian astronomer
Giuseppe Piazzi named Ceres. Ceres is now regarded as a dwarf planet. Ceres was
given dwarf planet status in 2006, along with Pluto, Eris, Makemake and Haumea.
Asteroids and Dwarf Planets and How to Observe Them (Astronomers' Observing
Guides) by Roger Dymock
Guide to the Universe: Asteroids, Comets, and Dwarf Planets (Greenwood Guides
to the Universe) by Andrew S. Rivkin