What process allows the frozen materials on a comet's surface to transform directly into gas as it approaches the Sun?

Answer

Sublimation

Sublimation is the physical process where a solid material bypasses the liquid stage entirely and turns directly into a gas. This process forms the coma.

What process allows the frozen materials on a comet's surface to transform directly into gas as it approaches the Sun?
Spaceastronomysolar systemcometparts