planetesimals

Planetesimals are small celestial bodies, typically a few kilometers to hundreds of kilometers across, that formed in the early solar system from dust, ice, and gas. They are the building blocks of planets, created through a process called accretion, where particles stick together due to gravity and electromagnetic forces. Over time, these planetesimals collided and merged, growing larger and eventually forming protoplanets and planets. Think of them as the primordial "seeds" out of which entire planetary systems developed billions of years ago.