Asteroids
Asteroids -1
(ceres)
(Vesta)
(ceres)
Most asteroids lie in a vast ring between the orbits of Mars and Jupiter. This main belt holds more than 200 asteroids larger than 60 miles (100 kilometers) in diameter. Scientists estimate the asteroid belt also contains more than 750,000 asteroids larger than three-fifths of a mile (1 kilometer) in diameter and millions of smaller ones. Not everything in the main belt is an asteroid — for instance, comets have recently been discovered there, and Ceres, once thought of only as an asteroid, is now also considered a dwarf planet. Many asteroids lie outside the main belt. For instance, a number of asteroids called Trojans lie along Jupiter's orbital path. Three groups — Atens, Amors, and Apollos — known as near-Earth asteroids orbit in the inner solar system and sometimes cross the path of Mars and Earth.
(Near Earth Objects)
Physical Characteristics :
Asteroids can reach as large as Ceres, which is 940 kilometers (about 583 miles) across and is also considered a dwarf planet. On the other hand, one of the smallest, discovered in 1991 and named 1991 BA, is only about 20 feet (6 meters) across.
Nearly all asteroids are irregularly shaped, although a few are nearly spherical, such as Ceres. They are often pitted or cratered — for instance, Vesta has a giant crater some 285 miles (460 km) in diameter.
As asteroids revolve around the Sun in elliptical orbits, they rotate, sometimes tumbling quite erratically. More than 150 asteroids are also known to have a small companion moon, with some having two moons. Binary or double asteroids also exist, in which two asteroids of roughly equal size orbit each other, and triple asteroid systems are known as well. Many asteroids seemingly have been captured by a planet's gravity and become moons — likely candidates include among Mars' moons Phobos and Deimos and most of the distant outer moons of Jupiter, Saturn, Uranus and Neptune.
The average temperature of the surface of a typical asteroid is minus 100 degrees F (minus 73 degrees C). Asteroids have stayed mostly unchanged for billions of years — as such, research into them could reveal a great deal about the early solar system.
Classification :
In addition to classifications of asteroids based on their orbits, most asteroids fall into three classes based on composition. The C-type or carbonaceous are greyish in color and are the most common, including more than 75 percent of known asteroids. They probably consist of clay and stony silicate rocks, and inhabit the main belt's outer regions. The S-type or silicaceous asteroids are greenish to reddish in color, account for about 17 percent of known asteroids, and dominate the inner asteroid belt. They appear to be made of silicate materials and nickel-iron. The M-type or metallic asteroids are reddish in color, make up most of the rest of the asteroids, and dwell in the middle region of the main belt. They seem to be made up of nickle-iron. There are many other rare types based on composition as well — for instance, V-type asteroids typified by Vesta have a basaltic, volcanic crust
( C-type asteroid)
( Asteroid 433 Eros , S-type)
( V-type)
Interesting Facts About Asteroids
Most asteroids are
covered in dust.
This dust is called regolith. It is
a rocky rubble more that dust and is the result of constant collisions in
space. These collision are between asteroids and any other body that crosses
their path. The larger object wins and ends up covered in the rubble from the
losing object. Sometimes space weathering has shown that some asteroids are OC
meteorites that are covered in regolith
Planets are not the only
ones with moons.
The spacecraft
Galileo proved that point in 1993 when it did a flyby of the asteroid 243 Ida
and discovered its moon dactyl. That was the first object to be found to have a
moon of its own that was not a planet. Several others have been discovered
since, but the first was the most exciting for astronomy.
Asteroids and planets share
a common birth.
The process
that helped form the planets is called accretion. During the beginning of the
universe when two bodies would collide they would stick together forming a
larger body. The planets and asteroids were formed in this manner. Obviously
the planets accrued more mass than most of the asteroids. But, as seen by the
asteroid Ceres being a dwarf planet, some asteroids came very close to
garnering enough mass and generate gravity just enough to possible become
planets in their own right.
