The Asteroid Belt was once a planet named "Maldek" out past Mars between Mars and Jupiter

 begin quote from:

Main Asteroid Belt: The majority of known asteroids orbit within the asteroid belt between Mars and Jupiter, generally with not very elongated orbits. The belt is estimated to contain between 1.1 and 1.9 million asteroids larger than 1 kilometer (0.6 miles) in diameter, and millions of smaller ones.

Asteroids: Facts - NASA Science

NASA Science (.gov)

https://science.nasa.gov › solar-system › asteroids › facts