👉 In astronomy, a planetesimal is a small irregular object that is composed of tiny grains or fragments of rock and metal. These objects are typically found in the outer planets' rings and orbiting the Sun. Planetesimals are often smaller than asteroids but larger than comets. Planetesimals can be classified into four main types: minor, medium, large, and supermajor (or "superplanetesimal"). Minor planetesimals are smaller than 10-20 meters in diameter,