Liquefaction of gases low temperatures, using, for example, turboexpanders. The liquefaction of air is used to obtain nitrogen, oxygen, and argon and other atmospheric noble gases by separating the air components by fractional distillation in a cryogenic air separation unit. Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded, each expansion results in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid. Air can also be liquefied by Claude's process in which the gas is allowed to expand isentropically
Atmosphere of Pluto heated, and its big thermal inertia (provided by non-volatile water ice) greatly slowed down its cooling. That is why gases, which now intensively evaporate from northern hemisphere, cannot quickly condense in the southern, and keep accumulating in the atmosphere, increasing its pressure. Around , the southern hemisphere will cool enough to permit intensive condensation of the gases, and they will migrate there from the northern hemisphere, where is polar day. It will last till equinox near aphelion (about 2113). The northern hemisphere will not lose its volatile ices completely, and their evaporation will supply the atmosphere even at the aphelion.