Skip to content


Planetesimals are solid, relatively small celestial bodies that form in protoplanetary disks and serve as the fundamental building blocks for planetary formation. Through the process of accretion, these objects gradually accumulate material, eventually contributing to the creation of larger planetary bodies.

Planetesimals are fundamental objects in the early stages of planetary formation, representing the building blocks from which planets eventually coalesce. They are solid, relatively small celestial bodies that range in size from a few kilometers to hundreds of kilometers in diameter. Planetesimals form as a result of the gravitational instability within the protoplanetary disk—a rotating disk of gas and dust that surrounds a young star.

Initially, within this disk, microscopic dust grains collide and stick together due to weak forces like van der Waals interactions and electrostatic forces. As these aggregates grow in size, they become planetesimals through a process known as accretion. Accretion involves the gradual accumulation of material as smaller particles collide and adhere, forming larger and more massive bodies. Planetesimals play a pivotal role in the formation of planets. Their collisions and mergers lead to the formation of larger bodies, known as protoplanets. These protoplanets can further grow through continued accretion until they become full-fledged planets. The study of planetesimals provides valuable insights into the conditions and processes that governed the early solar system’s dynamics and the origin of various planetary bodies.