Glossary

Accretion

Accretion is the process by which small particles and bodies stick together and grow into larger ones — the basic way planets are built.

Albedo

Albedo is the fraction of light a surface or planet reflects. High-albedo surfaces like ice reflect most light; low-albedo surfaces like ocean absorb it.

Frost Line

The frost line (or snow line) is the distance from a young star beyond which water and other volatile compounds can freeze into solid ice.

Habitable Zone

The habitable zone is the range of distances from a star where a planet with a suitable atmosphere could keep liquid water on its surface.

Magnetosphere

A magnetosphere is the region around a planet controlled by its magnetic field, which deflects much of the charged particle stream from its star.

Planetary Differentiation

Planetary differentiation is the process by which a molten planet separates into layers, with heavy metals sinking to form a core and lighter rock rising.

Protoplanetary Disk

A protoplanetary disk is the flat, rotating disk of gas and dust around a young star where planets form.

Roche Limit

The Roche limit is the distance from a planet within which tidal forces would tear apart a moon held together only by its own gravity.

Tidal Locking

Tidal locking happens when an orbiting body rotates exactly once per orbit, so the same side always faces the object it orbits.