Running water was present on Mars at the dawn of humanity

Thursday, March 05, 2009

Hellas Planitia, the area on Mars with the highest atmospheric pressure.

By which the article means 1.25 million years ago, so "walking upright and capable of using tools"-type dawn of humanity and not "writing epics like Gilgamesh"-type dawn of humanity. 1.25 million years is still a remarkably short time for there to be something as different from the Mars of today as running water on its surface:
Water that melted from ice and snow carved channels through a Martian gully and deposited a fan of mud at its mouth less than 1.25 million years ago — a recent time when early humans were walking upright and making tools on Earth, suggests a new study.

Previously, many scientists thought most water on Mars during that time period consisted of ice that sublimed directly into vapour and vice versa, with occasional bursts of liquid from groundwater sources, said Samuel Schon, lead author of the study.


Schon used a crater-counting technique developed for dating features on the moon and later adapted for use on Mars.

Large meteors that crash into the surface of a planet or moon leave behind craters. The impact resurfaces the area around its rim, leaving it smooth and flat like a newly repaved road. Over time, random impacts by smaller craters leave their mark on that surface, and it becomes more and more pock-marked as time goes on. By counting the craters on that new surface, researchers can estimate how long the crater has been there.

The gully fan studied by Schon is located near a large, fairly young crater. Using the crater-counting technique, it was estimated to be about 1.25 million years old.

What the article doesn't mention is that if you are able to prove and date running water on the surface of a planet like Mars, that also teaches us quite a bit about its atmosphere (and especially the rate of loss of the previously thicker atmosphere) because without the requisite air pressure liquid water can't exist. Apparently the only place that liquid water can exist on Mars is Hellas Planitia because its depth below the surface gives it an atmospheric pressure that is above the triple point of water.


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