In the late 1700’s, scientists saw that there was a big gap in between Mars and Jupiter.  They started to look for a missing planet. Instead of one large planet, they found many small planets or “asteroids” orbiting the Sun in a belt--the asteroid belt.

Asteroid means “star-like”. Asteroids are also called "minor planets" or "planetoids".  Scientists have identified more than 5,000 asteroids in our galaxy. Most are in the asteroid belt between Mars and Jupiter. There may be hundreds of thousands more.

The asteroids in the belt travel counterclockwise in a circular orbit. They orbit the Sun every 3.3 to 6 years. Some asteroids are the size of pebbles and others are as big as a city. If all the asteroids were lumped together, their mass would be smaller than the mass of the Moon. The largest asteroid is named Ceres. It is 634 miles (1020 km) across. Asteroids are irregularly shaped. They don’t have an atmosphere so they don’t have life. They have many craters.  Sometimes they crash into each other and shatter. Scientists think that the asteroids in the Asteroid Belt are left-over planet “ingredients”. Jupiter's gravitational pull kept the pieces from combining into a planet.

Some asteroids are a very dark color and may contain a lot of carbon. Others are a lighter color. Asteroids are made of stone or nickel and iron. Some asteroids are shiny like metal. Some day we may be able to mine the asteroids.

The asteroid belt is a fascinating part of our solar system.

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