Asteroid Belt: All What You Need To Know About Asteroid Belt

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Located at around 2.5 AU away from the Sun, or 2.5 times the distance between the Earth and the Sun, lies the famous asteroid belt. It is a region of space filled with bits and pieces of rock left over from the early stages of the solar system[1].

Many of these objects are also called planetoids, and they orbit between Mars and Jupiter in a pack known as the Main Asteroid Belt. These celestial objects are usually small, from the size of a boulder, but others are significantly larger.

Today we will answer some questions regarding the asteroid belt such as:

  • What is the origin of the asteroid belt?
  • What is the composition of the asteroid belt?
  • Are there different types of asteroids in the asteroid belt?
  • When was the asteroid belt discovered?
  • Which is the most significant object in the asteroid belt?
  • What will happen to the asteroid belt in the future?
Asteroid Belt
Credit: NASA

What is the origin of the asteroid belt?

In the early stages of the solar system, when dust and rock were pulled by gravity in the process of the formation of the very first planets, some debris was left alone to float around the sun.

The region between Mars and Jupiter later became what we today know as the asteroid belt. Many believe that these asteroids are remnants of a planet that was destroyed [2].

However, by calculating the entire mass of these celestial objects, numbers don’t add up. The combined mass is less than that of our Moon. Thus, it is too little actually to belong to a former planet. 

These objects were kept in place, stopped from blending with other planets due to gravitational interactions with the planet Jupiter. Throughout the universe, many other stellar systems contain such belts of debris, and it appears that it is actually common.

Studies regarding white-dwarf stars, which are stars nearing the end of their life, usually display signatures of rocky material, perhaps suggesting that such belts are conventional around dying systems as well.

What is the composition of the asteroid belt?

The majority of the asteroids located in this belt are made out of rock and stone. There are, however exceptions, some of them contain iron and nickel metals while others are a mix of these materials, along with carbon-rich materials. Asteroids that are farther away have even ice or water.

Asteroid Belt
Credit: NASA

Apart from different compositions, asteroids come in different sizes. Some are large, solid, with around 16 detected having a diameter greater than 150 mi / 240 km.

Some of the largest asteroids are:

  • Vesta
  • Pallas
  • Hygiea
  • Ceres

 The first three have diameters higher than 250 mi / 400 km. Ceres, on the other hand, has a diameter of around 590 mi / 950 km. It is the most prominent asteroid currently known, and it is also considered a dwarf planet.

Some asteroids are merely piles of rubble held together by gravity. Because most of them aren’t massive enough, their shape is irregular, sometimes resembling that of a potato.

Are there different types of asteroids in the asteroid belt?

There are many different types of asteroids in the asteroid belt. They are classified based on their chemical composition and their reflectivity or albedo. Here are some examples:

• C-type asteroids

C-type asteroids make up around 75% of the asteroid belt. The initial C stands for carbon. These asteroids have very dark surfaces, almost coal-black in appearance. Some meteorites discovered on Earth, such as the Carbonaceous chondrite meteorites, have a similar composition to these asteroids.

They are believed to be smashed up pieces from larger asteroids.  These asteroids dominate the belt and makeup around 40% of the closest asteroids to the sun. There are also subgroups such as B-type, F-type, and G-type.

C-Type Asteroids
Credit: NASA

• S-type asteroids

S-type asteroids make up around 17% of the belt. They are the second most common type of asteroids present there. They mostly dominate the inner asteroid belt, and their numbers dwindle farther out. They are bright and are composed of metallic nickel-iron mixed with magnesium-silicates. The initial S stands for siliceous.

• M-type asteroids

M-type asteroids are the last significant type with the initial M standing for metallic. They are relatively bright with most of them being composed out of pure nickel-iron. They usually reside in the middle of the belt.

The rarest types of asteroids are the A-type, D-type, E-type, P-type, Q-type, and R-type asteroids.

When was the asteroid belt discovered?

In the 18th century, a German astronomer by the name of Johann Titius noted a mathematical pattern in the layout of the planets and used it actually to predict the existence of one between Mars and Jupiter [3].

Many astronomers followed and searched the heavens for this missing body. In 1800, a group of astronomers known as the Celestial Police searched for the elusive planet. 

The first body discovered in this region was made by a nonmember, an Italian astronomer named Giuseppe Piazzi. He found and named Ceres. The second body found was Pallas, almost a year later [4].

These objects were considered planets for a time. However, as more objects were revealed in this region, observers noted that they were too small and too frequent to actually be planets, and started to refer to them as asteroids.

Which is the most significant object in the asteroid belt?

Probably the most significant object in the asteroid belt is Ceres, also holding the title of a dwarf planet. Though most asteroids are made out of rocky objects, Ceres is an icy body. It is the first asteroid to be discovered.

Ceres asteroid
Ceres asteroid, Credit: NASA

Modern observations conducted by the Dawn space probe strongly suggests the presence of organic material on Ceres. This led to the speculation that Ceres may have formed farther out in the solar system and later landed in the asteroid belt.

Ceres is vital for it may host water and thus life habitability. Some consider that life may have formed on Earth due to Ceres through the process of panspermia [5].

What will happen to the asteroid belt in the future?

The asteroid belt will continue to exist for millions of years. However, this might change when our Sun will near the end of its life. When this happens, in around 5 to 6 billion years, the sun’s light will probably shatter the asteroid belt.

The powerful radiation from this last light will warm up and destroy the asteroids [6].

Did you know?

– The term “asteroid” means starlike. This is because when they were discovered, astronomers thought that they looked like stars.

– There are millions of asteroids more than half a mile across in the asteroid belt.  There are even smaller asteroids than this, and they dominate when it comes to numbers.

– The average distance between asteroids in the belt is at around 600.000 mi / 1 million km. Thus a spacecraft can safely travel there and explore.

– If you were to stand on an asteroid, you wouldn’t be able to see the other ones due to the vast distance and their small size.

– The thickness of the asteroid belt has been estimated to be at around  1 AU.

– Many smaller groups of asteroids have been given names to distinguish them from the central belt. Some examples are the Lagrangians and Centaurs.

– There are different groups of asteroids that have different estimated ages. The Karin family is believed to have formed around 5.7 million years ago from a single object. The Veritas family formed at around 8.3 million years ago, while the Datura family dates at just 53,000 years ago.

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