What are Asteroids Made Of?

Asteroids are considered to be remnants of an early broken planet of the solar system. Asteroids have no fixed shape and are too small to be spherical in shape. They are ellipsoids (two dimensional figure), dumbbell or irregularly shaped.

As they have different shapes, they also vary in their size. The first asteroid Ceres, discovered in January 1801 by Italian astronomer Giuseppe Piazzi, is the largest known asteroid and is 940 km in diameter. Some of the smallest asteroids are just 6 meters in diameter. The mass of all the asteroids added together, is believed to lesser than than the mass of the Moon. Only 200,000 asteroids have been discovered so far, but billion more undiscovered asteroids still exit in our solar system.

Asteroid Belt

Most asteroids lie in the asteroid belt between Mars and Jupiter, however there are more belts in the solar system, namely the ones beyond Neptune's orbit. The belt itself has interesting origination theories. Most astronomers believe that the belt is a broken planet, while some say that the belt is primordial material that never coalesced into a planet because of Jupiter's gravitational pull. The asteroid belt lies between the orbits of Mars and Jupiter and contains more than 200 asteroids larger than 100 km in diameter, and more than 750,000 asteroids with diameters larger than 1 km. Most asteroids are found in this belt because of the gravitational interaction between the solar system and the celestial bodies in it.

As opposed to the fiction made popular by various depictions of the asteroid belt, it is not at all dense. The region is so vast that asteroids are hundreds of thousands of kilometers away from their closest neighbor. The asteroids are so small and far away from each other that they appear as faint stars, and except for Ceres, are not bright enough to be seen without some telescopic aid. Only the asteroid Vesta, on rare occasions of an extremely clear dark sky can become visible to the naked eye.

What are Asteroids Made Of?

Asteroids are made of different minerals and substances. This depends on the planet they broke away from in a collision, as well as the chemical reactions they might have experienced while orbiting in the solar system. The asteroids closest to the Sun are mostly carbonaceous and the ones further away are composed of silicate rock. The metallic asteroids are made of 70-80% iron and the remaining is nickel with many other metals such as iridium mixed in. Some are also made of half silicate and half metallic.

The asteroid Ceres is composed of a rocky core covered by an icy mantle, whereas Vesta has a nickel-iron core, basaltic crust and a covering of magnesium iron silicate (olivine mantle).

Asteroids composition has been classified as the following:

C class asteroids: They are found in the Earth's outer belt and are darker and more carbonaceous than the ones found in the S class.

D class asteroids: They are also known as Trojan asteroids of Jupiter and are dark and carbonaceous in composition.

S class asteroids: They are found in the Earth's inner belt, closer to Mars and are composed of mostly stone and iron.

V class asteroids: They are a far-out group of asteroids that follow a path between the orbits of Jupiter and Uranus, and are made of igneous, eruptive materials.

A near-Earth asteroid collided with the Earth about 65 million years ago, which triggered environmental changes, leading to the extinction of the dinosaurs. This asteroid created a huge circular depression called the Chicxulub Basin and is centered in Mexico's Yucatan Peninsula, a major tourist attraction. Though the chances of asteroid collision with the Earth is very rare, they do come very close to our planet due to collisions and gravitational tugs on the highly elliptical Sun's orbit. Most asteroids burn up in the atmosphere and never reach the Earth.

NASA projects, such as the Lincoln Near-Earth Asteroid Research (LINEAR) and the Near Earth Asteroid Tracking (NEAT) main objectives are to detect and intercept asteroids or other celestial bodies coming close to the Earth before they cause untold damage to our planet.