What Are Asteroids

Asteroids are rocky and metallic objects that orbit the Sun. These space objects never grew large enough to become planets. Scientists explain that asteroids are leftovers from the early solar system that formed over 4.6 billion years ago. When our solar system was young, dust and rock particles collided and stuck together. Most of these particles joined to form planets. However, some pieces never coalesced into larger bodies. These remaining fragments became the asteroids we observe today.

Most asteroids are small and have irregular shapes. Evidence shows that asteroids range in size from tiny pebbles to objects hundreds of kilometers wide. Unlike planets, which are large enough for gravity to pull them into spherical shapes, asteroids remain jagged and lumpy. Their composition varies, but many contain rock, metal, or a mixture of both materials. Scientists observe that some asteroids are made mostly of iron and nickel. Others consist primarily of rocky minerals similar to those found on Earth.

The asteroid belt is a region between Mars and Jupiter where most asteroids are located. This belt contains millions of asteroids orbiting the Sun. Scientists study asteroids because they provide clues about the early solar system. In 2001, NASA's NEAR Shoemaker spacecraft landed on asteroid Eros. This mission revealed detailed information about asteroid surface features and composition. Data from this mission helped scientists understand how planetesimals, or small planetary building blocks, behaved billions of years ago.

Understanding asteroids matters because they represent the original building blocks of planets. By studying these ancient objects, scientists can learn how Earth and other planets formed. Asteroids also help us understand the processes that shaped our solar system. Some asteroids may contain water and organic materials that could have contributed to life on Earth. Research on asteroids connects us to the earliest history of our planetary neighborhood.

Interesting Fact: The total mass of all asteroids in the asteroid belt is less than the mass of Earth's Moon. If all asteroids were combined into one object, it would be smaller than our Moon.