KATHMANDU: Asteroids, the minor planets can neither be classified either as a planet or as a comet.

These are in the direct orbit around the Sun — also known as the inner solar system. And, the larger forms of asteroids are called planetoids.

Asteroids are small, rocky objects that go around the Sun like planets. However, they are much smaller than planets.

On average, an asteroid the size of Apophis (370 meters) can be expected to impact Earth once in about 80,000 years.

Asteroids are made mostly of rock—with some composed of clay and silicate—and different metals — mostly nickel and iron.

However, some other materials are also found in asteroids.

The C-type (chondrite) asteroids are the most common. They consist of clay and silicate rocks. These asteroids are dark in appearance.

Likewise, the S-types (stony) asteroids  are made up of silicate materials and nickel-iron.

Similarly, the M-types are metallic (nickel-iron).

Some of these asteroids are large, and can even cause enormous destruction if they were to strike the Earth.

However, the estimated population in the Solar System is small and more than 90% of these are thought to have been discovered.

None of these asteroids pose any risk of impact.

Asteroids are, in fact, the left over from the formation of the solar system, which began about 4.6 billion years ago.

(With inputs from Agencies)