What condition allows volatile compounds like water to freeze beyond the frost line?

Temperatures being low enough

The differentiation between the inner, rocky planets and the outer, giant planets is fundamentally explained by the thermal profile across the protoplanetary disk, marked by a critical boundary known as the frost line or ice line. Beyond this specific distance from the central star, the temperature drops sufficiently low for materials that vaporized closer to the Sun—specifically volatile compounds such as water, methane, and ammonia—to transition from a gaseous state directly into solid ices. This dramatic increase in the quantity of available solid building blocks in the outer disk provided the necessary mass surplus for the cores of Jupiter and Saturn to grow large enough rapidly to capture vast amounts of primordial hydrogen and helium gas.