The largest desert on Earth is not the Sahara. It is Antarctica.
A desert is defined by how little precipitation falls, not by heat or sand. Much of Antarctica's interior gets less than 50 millimetres of precipitation a year, drier than most of the Sahara.
Why is this true?
Cold air holds very little moisture, so almost no snow falls inland; the ice sheet is the result of millions of years of tiny accumulations that never melt. Some Antarctic valleys have not seen rain for an estimated two million years.
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