How did planetesimals form?

The process is still not fully understood.

Planetesimals formed from dust and gas in the "protoplanetary disk".

Electrical attraction seems to be important in the early stages then gravity

brings things together.

The electrical forces are van der Waals forces.

Condensation, the process of forming solid particles from the solar nebula, is an early process in the formation of a planetesimal, an early solar system body of small to medium size that combines with otherplanetesimals to form protoplanets