Protoplanetary disk

A Baby Star surrounded by Protoplanetary Disc

A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may be considered an accretion disc because gaseous material may be falling from the inner edge of the disk onto the surface of the star, but this process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called proplyds.

Formation and evolution of the Solar System

Artist's conception of a protoplanetary disk

The formation of the Solar System is estimated to have begun 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.