The process of ice changing into water vapor without first turning into liquid water is called sublimation. During sublimation, ice releases energy in the form of heat and directly transforms into gaseous water molecules. Sublimation occurs when molecules on the ice's surface absorb enough energy to overcome the bonds holding them to other water molecules and gain kinetic energy, breaking free to form water vapor. This process primarily happens in environments with a temperature and relative humidity lower than the equilibrium sublimation point, allowing molecules with sufficient energy to escape directly from the ice.