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The Surprising Elements That Asteroids are Made Up Of

What are Asteroids Made Of?
Asteroids, also known as minor planets or planetoids, are small rocky and metallic celestial bodies that orbit the Sun. Read this UniverSavvy post to gain more information about these bodies, especially regarding their composition.
Loveleena Rajeev
Last Updated: Jun 7, 2017
Fast Fact
The first asteroid called Ceres, discovered in January 1801 by Italian astronomer Giuseppe Piazzi, is also the largest known example of such celestial bodies, and measures about 940 km in diameter.
Asteroids are considered to be remnants of an early broken planet of the solar system. They have no fixed shape, and are too small to attain a spherical appearance. They are generally characterized as ellipsoidal, dumbbell, or irregularly shaped. These celestial bodies also vary in their size. Some of the smallest ones are just 6 meters in diameter. The mass of all the asteroids added together is believed to be lesser than that of the Moon. Only about 200,000 of these celestial bodies have been discovered so far, but billions of undiscovered ones still exist in our solar system. Ceres, Pallas, and Vesta are some of the largest asteroids, and were also among the first ones to be discovered. Preliminary research is now going on whether some of these asteroids can be mined for their rich mineral content.
Asteroid Belt
Asteroid belt between Mars and Jupiter
Asteroid belt between Mars and Jupiter
Numerous asteroids lie in the belt between Mars and Jupiter. However, there are more belts in the solar system, namely the ones beyond Neptune's orbit.
Many astronomers believe that the belt between Mars and Jupiter is the result of a broken planet, while some say that it is a type of primordial material that never coalesced into a planet, because of Jupiter's gravitational pull. Most asteroids are found in this region of space as a result 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. They are so small and distantly placed 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 Vesta can be visible on rare occasions of extremely clear and dark skies.
Composition of Asteroids
Asteroids are made up of different minerals and components. 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.
Sun attacked by asteroids
The ones closest to the Sun are mostly carbonaceous, and the ones further away are mostly composed of silicate rocks.

The metallic asteroids are made of 70-80% iron, and the remaining percentage consists of a mixture of nickel with other metals like iridium. Few examples are also made up of silicate and metallic components in equal proportions.
Some asteroids are characterized by the presence of dust layers called regolith. These layers are mainly formed because asteroids frequently collide with each other. This results in the separation of loose fragments of rocks and associated dust called regolith.
According to several studies, asteroids also show traces of organic compounds along with amino acids in their rocky layers. This probably indicates that as amino acids are very important for the existence of life, organisms first appeared on the Earth mostly due to asteroid collisions.
Asteroid Ceres
Asteroid Ceres
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).
Methods used: Several techniques have been used to study the composition of asteroids, the most important methods being telescopic spectroscopy, asteroid spectrophotometry, reflection spectroscopy, etc. These techniques use the principle that different minerals and components show variation in absorption of light rays, depending on their wavelength and frequency.
Through spectral analysis of the light rays reflected from the surface of asteroids, it has been interpreted that on a microscopic scale, these celestial bodies are composed of minerals like pyroxenes (both ortho and clino), plagioclase feldspar, olivine, iron and magnesium silicates, etc. This is hypothesized on the basis of variations in graphs that are an outcome of such techniques.
Classification of Asteroids According to their Composition
C class asteroids
They are found in the exterior regions of the main asteroid belt, and are darker and more carbonaceous than the ones found in the S class. They represent the most common type of these celestial bodies, i.e., over 75% of asteroids belong to this class. They have a similar composition as that of the Sun, and are characterized by a bluish-colored spectrograph.
D class asteroids
These dark-colored celestial objects are mostly made up of carbonaceous content, and are also known as the Trojan asteroids of Jupiter. Several studies indicate the presence of carbon monoxide in a frozen form, and the presence of water beneath their surface mainly in the form of ice.
S class asteroids
These celestial bodies are present closer to Mars, and are composed of mostly iron in the form of silicates. Magnesium silicate is also found in equivalent proportions. About 17% of all the asteroids belong to this category, and are majorly present in the inner asteroid belt. These types are characterized by a red-colored surface.
V class asteroids
They are a distant group of celestial bodies that follow a path between the orbits of Jupiter and Uranus, and consist of igneous materials, i.e., are magmatic in composition. The surfaces are mainly composed of basaltic and rhyolitic minerals, and are characterized by dominance of pyroxenes (a mineral group found in igneous rocks).
M class asteroids
They are a rare type of asteroids, and made up of iron and nickel, i.e., they are metallic in nature. In the past, they were mainly situated closer to the Sun, and hence, due to initial melting, the subsequent differentiation led to the formation of metallic iron core surrounded by nickel.
Chicxulub Basin: An Asteroid Impact
Near-Earth asteroid
A near-Earth asteroid collided with the Earth about 65 million years ago, which triggered several environmental changes, leading to the extinction of dinosaurs. This asteroid created a huge circular depression called the Chicxulub Basin, which is centered in Mexico's Yucatan Peninsula, and is 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 within themselves and gravitational tugs on the highly elliptical Sun's orbit. Most asteroids burn up in the atmosphere and never reach our planet.
The objectives of NASA projects, such as the Lincoln Near-Earth Asteroid Research (LINEAR) and the Near Earth Asteroid Tracking (NEAT) are to detect and intercept asteroids or other celestial bodies coming close to the Earth, before they cause extreme damage to our planet.