Asteroids: The Rocky Leftovers

Asteroids are chunks of rock and metal that never became planets. Early in the Solar System’s history, lots of material was orbiting the Sun. In the region between Mars and Jupiter, Jupiter’s gravity kept stirring things up, preventing those rocks from forming a full planet.

The asteroid belt is not a dense “minefield” like movies show—objects are usually very far apart. But it is still a huge reservoir of ancient material that tells us what the early Solar System was made of.

Some asteroids have orbits that bring them near Earth. Space agencies track many of them, not because panic is needed, but because early warning is the whole game.