ASTEROIDS

What is an asteroid?

An asteroid is a relatively small, rocky or metallic body that orbits the Sun. I say relatively because these objects vary wildly in size, with many being smaller than a car and some being larger than entire U.S. states! We typically start calling an object an asteroid when it exceeds one meter in diameter and stop calling them asteroids when their mass becomes sufficient to gravitationally crush themselves into a spherical shape (like planets). Most asteroids are remnants left over from the formation of the solar system about 4.56 billion years ago. When the young protostar was surrounded by a rotating disk of gas and dust called the protoplanetary disk, tiny solid particles collided and stuck together, gradually building into larger objects:

dust particles > pebbles > rocks > asteroids > planetesimals > protoplanets > planets

Asteroids are largely the material that never made it into a planet.

We know of over one million asteroids floating around in our solar system but there are likely far more we haven’t discovered yet because they are too small, dark or distant.