Asteroid Belt


The asteroid belt is in the far region of the solar system between Mars and Jupiter. This is where a majority of the asteroids in our solar system are found.

While they form in the asteroid belt, there are other asteroids that orbit in space as close as near-Earth.

The asteroid belt contains asteroids of all different sizes, but there are four that are the largest: Ceres, Vesta, Pallas, and Hygiea. These four asteroids contain half of the mass that is in the entire asteroid belt.

Asteroid Belt

Scientists believe that if you combined all of the asteroids in the belt that it would make up a fifth rocky planet smaller than the Earth’s moon.

Asteroid Belt Statistics:

  • Location: 2.2 and 3.2 astronomical units (AU) from the sun.
  • Average Distance between objects: 600,000 mi/965606.4 km

History of the Name:

In the 18th century scientists used mathematics to try to predict the layout of the planets and to find a potential planet between Mars and Jupiter.

The 18th century German astronomer, Johann Titius played an important role noting the mathematical pattern. In 1800, the Celestial Police was formed to search the heavens for the so-called “missing planet.”

The group consisted of 25 astronomers, each one searching 15 degrees of the Zodiac. However, it was a nonmember that discovered the first body, and Italian astronomer Giuseppe Piazzi named it Ceres.

Solar System

The second body was found a bit over a year later and it was named Pallas. For quite a long time, scientists assumed that these were both planets, but by the 19th century more than 100 celestial bodies in this area had been found.

These were too small to be considered as planets and so they called them asteroids, or “star-like.” Piazzi is given credit for the discovery of the asteroid belt.


When our solar system was in its early life, rock and dust circled the sun and were drawn together by gravity that eventually formed our planets and moons.

However, not all of the debris that was used to make these new worlds and the leftovers ended up in an area between Jupiter and Mars. Some scientists once thought that the asteroid belt could have been the remains of a destroyed planet but this was debunked when NASA configured the total mass of everything in the belt to be less than our moon.

This means this there is not enough debris to create a planet. The leftovers are held in place by the gravitational pull of Jupiter and since the pieces are so far apart they never got close enough to each other to try to become another planet or moon.

asteroid belt Formation

Scientists have observed the asteroid belt as part of their attempt to understand the solar system. They developed a theory called the “Grand Tack” that helps to explain the origins of the asteroid belt.

The theory indicates that in the first 5 million years of the solar system development, Saturn and Jupiter were thought to be close to the sun and then changed direction to head out to the outer solar system.

As they moved outward they scattered the original asteroid belt and then sent objects back in to fill it up again. The theory may hold weight as since that time astronomers have seen other star systems that also have their own asteroid belt, so this may be common in the formation of some solar systems.

Additional studies have shown signs of asteroid belts around dying solar systems.

The Main Belt of the asteroid belt is between Jupiter and Mars and is around 2-4 times the Sun-Earth distance.

It spans about 140 million miles across. Objects that exist within the belt are divided into 8 subgroups, with each one named after the main asteroids within the group:
Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas.

Structure and Surface:

Almost all of the asteroids in the Main Belt are made up of stone and rock, however, a small percentage of them contain nickel and iron metals. The rest of the asteroids are made up of a complete mixture of all of these as well as some materials that are carbon-rich.

Those asteroids that are the most distant have a tendency to contain higher percentages of ices. While none are large enough to maintain an atmosphere, there is evidence that water is on some asteroids.

Some of the asteroids are little more than a pile of rubble held together by gravity. If you looked at them they would look like rocks or stones that are glued together. Planets and moons are spherical and the shape is due to stronger gravitational forces.

Asteroids in the belt don’t have a strong enough gravity so their shape and structures are irregular. Many have an appearance of a lumpy potato. The 216 Kleopatra asteroid looks almost like a dog bone.

Asteroids in general are classified into several types; each one is based on their reflectivity or “albedo” and composition.

  • C-type asteroids: Almost 75% of the known asteroids fall into this classification. They are called “C” because they are made up of mostly carbon. The surfaces are dark grey to coal-black. On Earth we have similar composition in the carbonaceous chondrite meteorites that are believed to be chucks or pieces of the larger asteroids that were broken off and fell to the surface. The ESA (European Space Agency) has indicated that the C-type asteroids dominate the belt region, they are only around 40% of the total asteroids that exist near the sun. These are further dividied into the subgroups of B-type, F-type, and G-type.
  • S-type asteroids: These make up around 17% of the known asteroids and are the second most common type. The “S” represents the word “silicaceous.” Most of them are in the inner asteroid belt, but you find fewer as you expand out. The composition of metallic nickel-iron that’s mixed with iron and magnesium silicates also gives them the property of being brighter.
  • M-type asteroids: This is the last of the major groups, with the “M” representing the word “metallic.” They are also rather bright due to the content of pure nickel-iron. These asteroids are most common in the asteroid belt’s center region.
  • There are some additional asteroid types including: A-type, D-type, E-type, P-type, Q-type, and R-type.

Atmosphere. Magnetosphere, and Moon Status:

Asteroids don’t have any atmosphere and a majority have only a slight gravity. For those asteroids that are made up of multiple “rocks” the gravity is just barely strong enough to hold them together.

Asteroids don’t have any rings, however, scientists are finding that some rare asteroids that are the size of small planets, do have small moons.

Could Life Exist?

Asteroids don’t have any sort of stability in orbit and are not conducive to being able to maintain life as we know it. While some asteroids have been shown to have ice-water, they don’t have any atmosphere.

Interesting Information:

You might think of the asteroid belt as an area packed with asteroids just waiting to hit each other. In reality, there is an incredible amount of distance between the asteroids that are in the belt. If you had the ability to stand on one, the next one would be so far away that you couldn’t really see it.

When an asteroid or even part of an asteroid hits the earth it is called a meteorite.

There are a number of different types of meteorites, each made of a different composition:

Iron meteorites

  • Iron: 91 percent
  • Nickel: 8.5 percent
  • Cobalt: 0.6 percent
  • Stony meteorites
  • Oxygen: 6 percent
  • Iron: 26 percent
  • Silicon: 18 percent
  • Magnesium: 14 percent
  • Aluminum: 1.5 percent
  • Nickel: 1.4 percent
  • Calcium: 1.3 percent

The collision on Earth of asteroids from the asteroid belt and comets may have contained enough water-ice as well as other carbon-based molecules to jump-start the planet to life.

During the early years of Earth’s development some asteroids kept life from surviving, but once things calmed down a bit the collisions delivered the water and elements that encouraged life.

Companies in countries around the world having been taking note of the idea of asteroid mining. We know that it will only be a matter of time before we use up many of the Earth’s important elements.

Scientist have estimated that if we continue to use the resources of the Earth at the current rate, we could run out of many of the key elements within 50-60 years.

Asteroids can be a good source for silver, phosphorous, tin, gold, lead, indium, and copper. Space missions designed to mine asteroids will be expensive and require sophisticated processes.

Mining the raw materials that may be abundant on asteroids can be a tricky business, but there are a number of corporations that are looking into this as a good alternative.

Space Visits:

  • New Horizon: launched 2006: New Horizon traveled through the asteroid belt on its way to visit and study the dwarf-planet Pluto and its moons.
  • Dawn: launched in 2007: the mission was to journey 4.3 billion mi/6.9 km to arrive at the asteroid belt and orbit and observe the dwarf planets Vesta and Ceres. The discoveries of Dawn included reinforcing the theory that dwarf planets could have had oceans throughout their history and possibly still do. The information sent back from Dawn also showed that the two planet-like worlds had completely different evolutions.

Facts about Asteroid Belt for Kids:

  • Every year, a meteoroid the size of a car hits the atmosphere of the Earth and is viewed as a fireball as it burns up in the atmosphere.
  • It’s believed that asteroids may have delivered much of the water to Earth as it was developing.
  • About once every 2,000 years the Earth has an impact of an asteroid that is near the size of a football field.
  • Most of the asteroids are in the main asteroid belt area between Jupiter and Mars, however, there are other known “belts” in the solar system area including the Lagrangians and the Centaurs. To avoid confusion, the name “main belt” was given for standard asteroids.
  • Some of the asteroids that exist are actually comets that have been blown out after the ice is gone.
  • Some asteroids also fall into the classification of planetoids or minor planets.
  • Scientists believe that during the asteroid belt formation, a lot of the objects that were floating around began to crash into each other and fuse together, forming protoplanets; however it was Jupiter’s intense gravitation that may have pulled them apart.
  • It’s thought that there are around 0.7-1.7 million asteroids that have a diameter of 1 km or bigger and nearing 200 asteroids with a size that’s larger than 100 km.

Escape from the Asteroid Belt:

Scientists believe that it is thanks to the intense gravity of Jupiter that asteroids don’t escape that often from the asteroid belt. However, occasionally, asteroids do slam into each other with such great power that it jettisons them outside of Jupiter’s hold.

The evidence of this can be seen on our moon and other planets that don’t have active weather to cover up the evidence of their impact.

Many asteroids have struck the earth since it was formed 4.5 billion years ago. Thanks to improved technology, scientists are able to examine areas of the Earth that had impacts and are now completely covered due to weather and erosion.

The most devastating impact is believed to have been the one to hit the Yucatan Peninsula, causing the death of the dinosaurs. An asteroid that would be considered to be capable of a global disaster for Earth would need to be over ¼ mile wide.

If an asteroid of that size hit Earth it would cause enough dust to rise into our atmosphere that the Earth could have a “nuclear winter.” NASA officials indicate that an asteroid of any great size strikes the Earth only around one time every 1,000 centuries.

Smaller asteroids do escape the asteroid belt due to impacting each other and hit the Earth every 1,000-10,000 years. The word “small” should be understood that these are large enough to destroy cities and create huge tsunamis.

NASA has indicated that space rocks that are smaller than 82 feet/25 m are mostly likely to be burned up in the atmosphere of Earth before they hit the surface.