Protoplanetary disk

When a portion of a molecular cloud reaches a critical size, mass, or density, it begins to collapse under its own gravity.

Observations by the Hubble Space Telescope have shown proplyds and planetary disks to be forming within the Orion Nebula.

[12] The mass of a typical proto-planetary disk is dominated by its gas, however, the presence of dust grains has a major role in its evolution.

Dust grains shield the mid-plane of the disk from energetic radiation from outer space that creates a dead zone in which the magnetorotational instability (MRI) no longer operates.

[14] The dead zone located at the mid-plane can slow down the flow of matter through the disk which prohibits achieving a steady state.

This process competes against the stellar wind, which drives the gas out of the system, and gravity (accretion) and internal stresses (viscosity), which pulls material into the central T Tauri star.

The Earth's moon likely formed after a Mars-sized protoplanet obliquely impacted the proto-Earth ~30 million years after the formation of the Solar System.

Based on recent computer model studies, the complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth.