Astronomy
The Geology and History of Liquid Water on Mars
Quick fact
The youngest known lake on Mars may have existed around 110,000 years ago, possibly formed by melting snow from a past ice age—evidence that liquid water can appear even in the Amazonian period.
Why this is interesting
Mars looks like a bone-dry desert today, yet its planet-wide valleys, deltas, and lakebeds reveal that rivers and lakes once carved this world. What happened to all that water?