Which continent is the driest on Earth?

Deserts are defined by how little precipitation they receive, not by heat, and by that measure Antarctica wins outright. Extremely cold air holds almost no moisture, and the continent is ringed by circulating winds that discourage weather systems from penetrating the interior, so the high polar plateau receives less annual precipitation than the Sahara. The ice sheet is thick only because what does fall essentially never melts, accumulating over hundreds of thousands of years. Parts of the continent are drier still: the McMurdo Dry Valleys are ice-free stretches of bare rock and gravel where katabatic winds sweeping down from the plateau evaporate any snow before it can settle, and where some areas may not have seen meaningful rainfall for a very long time. Those valleys are studied as one of the closest terrestrial analogues to the surface of Mars, which is a strange thing to say about the wettest-looking continent on any map.

Antarctica's ice preserves a layered record of past atmospheres, which is why deep cores drilled there reveal ancient air bubbles.