Perez
Perez
Perez
Nathaniel Perez
Date:08/21/18
Per: 6
1 Asteroid is a rocky or metallic object smaller than a planet that orbits a star.
Astronomers have discovered asteroid belts around other stars. This article,
however, will discuss asteroids in our own solar system. Most asteroids orbit the
sun between the orbits of Mars and Jupiter. This region is known as the Main Belt.
Millions of asteroids may exist. Astronomers think that most of them measure less
than 6 miles (10 kilometers) in diameter. The majority of asteroids have a rocky
composition. Some consist of metal or a mixture of metal and rock. People
sometimes call the asteroids minor planets. That term has no formal definition in
astronomy, however. The International Astronomical Union (IAU) is a widely
recognized authority in naming heavenly bodies. According to the IAU, no
asteroid is large enough to be considered a planeet. The IAU classifies Ceres, the
largest asteroid, as a dwarf planet.
Scientists think that asteroids consist of material left over from the formation of
the solar system. Such processes as erosion and volcanic activity have altered the
planets and moons. But much of the material in asteroids is almost unchanged.
Much of our knowledge of asteroids comes from studying meteorites, pieces of
matter that have fallen to Earth from asteroids.
2 Sizes and shapes. Ceres’s longest diameter measures 605 miles (975
kilometers). Ceres makes up more than one-fourth of the total mass (amount of
matter) of the Main Belt asteroids. The next largest asteroids are Pallas and Vesta.
Each stretches slightly over 300 miles (500 kilometers) in diameter. The tiniest
asteroids may be pebble-sized. They would be too small to be seen by Earth-based
telescopes.
Occasionally, a large asteroid will break apart into many smaller ones, usually as
the result of a collision. For this reason, smaller asteroids are far more common
6 M-type asteroids. Most of the remaining asteroids belong to the third major
group, the M-type asteroids. These bright objects consist of nearly pure nickel-
iron. They may be fragments of the metallic core of a larger body that broke apart.
Other asteroid types are relatively rare. One such group, the D-type asteroids,
occurs more frequently in the outer solar system. They appear more unchanged
than asteroids of the inner solar system. The sun's heat has modified the
compositions of the asteroids in the inner solar system.