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The air on Mars is so thin that liquid water at the surface would boil away rather than pool.

Astronomy Facts, sourced to NASA.

What it means

Boiling happens when the pressure pushing down on a liquid drops below its vapor pressure, and on Mars the atmosphere is under a hundredth of Earth's. Water there tends to go straight from ice to vapor without a liquid stage. That does not mean Mars is dry. There is a great deal of ice at the poles and under the surface, and the landscape is carved with channels cut by water long ago.

The claim comes from NASA, and the page it comes from was read on 2026-08-27 to confirm it still says this.

This is not the kind of claim that goes out of date, which is why it was set as a puzzle rather than a fact with a shelf life.

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