Asteroid Belt Facts
Asteroid Gaspra
Close up image of the asteroid 951 Gaspra which is 10 miles (17 km) in length
  • There are 200 objects in the asteroid belt larger than 60 miles (100 km) in diameter and almost 1 million objects over 1 km in diameter.
  • The average surface temperature of an asteroid is -73C (-100F).
  • The largest asteroid Ceres was the first to be discovered in 1801, it has recently been re-classified as a dwarf planet.
  • Asteroids are rich in minerals, the estimated wealth of the asteroid belt is 100 billion dollars for every person on Earth today.
  • The study of asteroids can give us a valuable insight into how the planets formed.
  • A meteorite is any fragment from a body, such as an asteroid, which manages to pass through our atmosphere and land on Earth.
  • Some asteroids orbit in the inner solar system and indeed some even cross the orbit of Earth, these are known as Near Earth Objects (NEO).
  • It is believed an asteroid impact in the Gulf of Mexico was responsible for the extinction of the dinosaurs 65 million years ago.

The Asteroid Belt

asteroid with its own moon
An asteroid with its own tiny moon
The asteroid belt is situated between the orbits of Mars and Jupiter around 280 million miles (450 million km) from the sun. There are millions of asteroids residing in this area ranging from 600 miles (950 km) in diameter, all the way down to particles of dust. It is believed asteroids are the remnants from the formation of the planets.
Although there are millions of objects in the asteroid belt it is not densely populated, they are scattered over a vast area, several spacecraft have passed through the belt on their way to the outer planets without encountering any issues. The main danger we face on Earth from the asteroid belt is that objects escape from the region and collide with the planets and moons in our solar system. Near Earth asteroids are tracked by NASA and other organizations.

Asteroids - The Threat to Earth

Arizona impact crater
The 1 kilometer wide Barringer Crater in the Arizona desert caused by an asteroid strike.
The threat to life on Earth from a large asteroid impact is very real and has happened before in the planet’s history. Sixty five million years ago an asteroid 10 kilometers in diameter struck the Yucatan Peninsula in the Gulf of Mexico. The explosion created was enormous, immediately destroying everything within a radius of 500 kilometers, the shock wave from the impact travelled hundreds of miles causing large scale fires, triggered huge tsunamis and a chain reaction of volcanic activity and earthquakes. Trillions of tons of dust were thrown into the atmosphere and carried around the globe by high winds shrouding the planet in darkness for many months to come, causing temperatures to plunge. This event led to the extinction of more than half of all the species on Earth including the dinosaurs.

An impact as large as the one that caused the extinction of the dinosaurs may be extremely rare but smaller asteroids which are also capable of mass destruction strike the Earth much more frequently. Asteroids with a diameter of between 1 to 2 kilometers impact the Earth every 100,000 years or so and are also capable of causing damage on a global scale and could even threaten our existence. Maybe the most worrying threat comes from smaller objects of around 50 meters in diameter as they hit the Earth around every 1,000 years, these smaller objects are capable of destroying a large city. In 1908 an asteroid 50 meters in diameter entered Earth’s atmosphere and exploded over a remote area of Russia. The explosion created was the largest ever in modern human history, 1000 times greater then the atomic bomb which landed in Hiroshima, laying waste to an area of over 2,000 square kilometers.

As well as their destructive qualities asteroids have also had a huge influence in the evolution of life on Earth, an influence that has been extremely beneficial for us. Up until the Yucatan Peninsula impact the dinosaurs were the dominant species and had been for millions of years, small rodent like creatures called mammals also existed at the time but in sparse numbers and mainly restricted themselves to living underground. The extinction of the dinosaurs changed all that and the mammals began to flourish, evolving into more complex and intelligent life forms, eventually leading to the evolution of mankind. It could be argued that destructive events on a global scale such as this are an integral part of evolution, without them human beings would not exist.

Missions to the Asteroid Belt

ion engine Launch: September 2007
Arrival: Vesta - July 2011 / Ceres - March 2015
Agency: NASA
Summary: Dawn is the first spacecraft to orbit one object then after a period of time leave and continue to another body, this is thanks to its ion propulsion engine (pictured left). Although less powerful than a conventional chemical rocket, ion engines are a lot more fuel efficient, allowing them to run for longer.

Dawn has studied two objects in the asteroid belt, the large asteroid Vesta and the dwarf planet Ceres. In the first part of its mission the craft successfully entered into orbit around Vesta in July 2011, taking high resolution images and studying the asteroid over a period of 15 months. In March of 2015 Dawn successfully entered into orbit around the dwarf planet Ceres and began studying its surface in late April.

The goal of the mission is to characterize the conditions of the early solar system and the role of water and size in determining the evolution of the planets.