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Last updated date: 23rd May 2024
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What is an Asteroid?

The small bodies orbiting around the sun with a diameter less than 1000km or 600 miles are known as Asteroids. The asteroids are also known as minor planets or planetoids. Most of the asteroids are orbiting around the sun between Mars and Jupiter and form a flat ring surface called the asteroid belt. Many asteroids in the universe look similar to the planets but they are in relatively large groups and smaller in size. So, scientists kept them as individual objects and kept them under the terms of minor plants based on their physical properties. The major differences between asteroids and meteoroids are their size. The asteroid size is larger than he size of meteoroids. 

This article describes the origin, classifications of asteroids, major milestones in asteroid research with size and facts of asteroids are explained in detail. 

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Origin of Asteroids

According to the dynamical model, the asteroids in the universe are formed during the first million years after the formation of the solar system with the gravitational interaction among the giant planets, especially between Jupiter, Saturn, Uranus, and Neptune. The asteroids in the universe initially started moving towards the sun and then moved outwards away from the sun. Meanwhile, the asteroid belts evolved because of the collision among asteroids. The evidence for a collision of asteroids is found in the dynamical asteroid families. Due to the collision of asteroids, the asteroids became smaller than 40 km and sometimes, they get diverted from their orbits due to solar radiation. 

Major Milestones in Asteroid Research and Asteroids Facts

On 1st January 1804, the astronomer Giuseppe Piazzi at Palermo from Italy was the first person to discover the asteroids. Initially, Piazzi discovered a comet and later he studied the object in the orbital elements. According to him, asteroids are found between the orbits of Mars and Jupiter. These planets-like objects are moving in the orbit between Mars and Jupiter. But he could not continue his research on asteroids after the 11th of February 1804. He also attracted the observation of a few astronomers, by publishing their reports in the press. But some astronomers did not believe his research.

In 1801, the German mathematician Carl Friedrich Gauss made a few observations on the methods for computing the orbit of minor planets. Later, German Hungarian astronomer, Franz von Zach kept Gauss’s predictions and rediscovered the objective of Piazzi in late 1801’s. They named the object Ceres, which is the name of the ancient Roman grain goddess and patron goddess of Sicily.

In the next six years, astronomers found three more faint objects that are similar to early asteroids namely Pallas, Juno and Vesta and found that the asteroids are the broken pieces of the exploded planets. In 1845, Karl L. Hencke renewed the research of flurry and discovered a fifth asteroid also named Astraea.

As of 1866, Astronomers found 88 asteroids. An American astronomer, Daniel Kirkwood researched the distribution of asteroids and their distance separation from the sun. In 1891, astronomers introduced photography for making research on new asteroids and identified about 322 asteroids. At the end of the 19th century, they found about 464 asteroids and it reached up to 108,066 at the end of the 20th century.  During the 21st century, it reached above 1,000,000. In the research, they found that more than 90 percent of the asteroids were less than one kilometre. These orbits can also cross the orbit of earth and also have the potential to collide with the planets. As of 2020, astronomers have found about 990,933 asteroids; in that, about 55 percent were named.

Geography of the Asteroid Belt

The geography of the asteroid belts is mainly described in their features. Asteroids are mainly coordinated with the latitude, longitude, and altitude for finding their exact location in the universe. Similarly, any objects in the solar system can be identified with the three parameters namely, heliocentric ecliptic longitude, heliocentric ecliptic latitude, and heliocentric distance. But the positions found through this method will be valid for certain periods of time because all the objects in the universe are moving continuously. The path of the object in the solar system is called orbit, with which the object will revolve around the sun. 

All the asteroids in the universe move around the sun in elliptical orbits as in the direction of the major planets. Some elliptical orbits look like circles or eccentric. It is possible to predict the past and future location of the asteroids by finding their orbit. The orbits are mainly used to describe the geographic location of the asteroid belt. 

Classification of Asteroids 

Based on the composition, the asteroids are mainly classified into three types. They are listed below. 

  • The most common type of asteroid is C-type (chondrite) asteroids. The main composition of C-type asteroids is clay and silicate rocks.  These are the most ancient objects in the solar system and look dark in colour. 

  • The stony asteroids or S-type asteroids are made up of silicate materials and nickel-iron. 

  • The metallic or M-type asteroids are mainly made of nickel-iron. They are located far away from the sun and some of these asteroids may experience high temperatures even after partial melting. These asteroids have iron sinking to the centre and forcing basaltic (volcanic) lava to the surface.

Asteroids are also classified into three types based on their geographical location. They are listed below. 

Main Asteroid Belt 

Most of the asteroids are orbiting around the sun between Mars and Jupiter within the asteroid belt. This main asteroid belt contains about 1.1 to 1.9 million asteroids, whose asteroid size is more than 1-kilometre diameter. The asteroid belt also contains millions of smaller asteroids. The asteroids in the main asteroid belt do not have very elongated orbits. During the origin of the solar system, these asteroids formed a new gravitational field between Jupiter and created the planetary bodies in this region. Also, the small bodies collide with one another and are fragmented to form asteroids. 


The asteroids which share their orbits with larger planets but do not collide with planets are known as Trojan asteroids. Because the asteroids and planets are placed in different places in orbit. This is called the L4 and L5 Lagrangian points. Here, the gravitational force among the planets in the orbit and the sun balances the trojans. Or else, the trojans may fly out of orbits. The population of Trojan asteroids is more in Jupiter. The Trojan asteroids are found between the orbits of Mars, Neptune. In 2011, astronomers from NASA discovered the Earth trojan. 

Near-Earth Asteroids

The asteroids, whose orbits are closely passed through the orbit of the earth are known as Near earth asteroids. The asteroids, which actually cross the earth’s orbital, are known as Earth-crossers.

This article described the origin of asteroids, the classification of asteroids, the size and facts of asteroids with the geography of the asteroid belts. 

FAQs on Asteroids

Q1. What is an asteroid made of?

Asteroids may be made of clay and silicate rocks. That may appear dark in colour. Asteroids are ancient objects in the solar system. Here, the asteroids are made of silicate materials and nickel-iron are called S-type (stony) asteroids. The asteroids made of metallic components are called M-types asteroids.  

Q2. What exactly is an asteroid?

A small, rocky object that revolves around the sun as planets are called an asteroid. The size of asteroids is much smaller than the planets. The solar system has many asteroids and most of the asteroids are located in the asteroid belts between Mars and Jupiter.

Q3. Why do asteroids fall?

Usually, asteroids will revolve around the sun in a particular direction and they are enough for the orbits not to degrade. But sometimes, asteroids slow down and fall towards the sun, or towards Jupiter or towards Mars. 

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