Space

An accounting of all the water that should have been and gone on Mars’s surface has come up with a discrepancy that shows just how little we understand the Red Planet’s hydrological history

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An artist’s impression of Mars millions of years ago, when it had more water on its surface

ESO/M. Kornmesser/N. Risinger

Planetary scientists agree that Mars used to have liquid water on its surface and a water-rich atmosphere, far different from its current arid state. But an accounting of all the sources of water to the Martian surface and all the ways it could have been taken away has found a major discrepancy – we simply don’t know where all that water went.

The period when Mars is thought to have had liquid water, between about 4.5 billion and 3.7 billion years ago, is known as the Noachian Period .…