On September 18th, 2016 we learned about

Large Martian lakes somehow outlasted the planet’s atmosphere

It looks like we missed boating on Mars by less than we’d thought. Sure, the strongest signs of water on the Red Planet are currently dark streaks in the sand, but a mere two to three billion years ago, the place was likely lousy with water. Everything from a large ocean to streams and lakes seem to have left their mark on the planet’s surface, some of it possibly from a time when things should have been too cold for water to really flow anywhere. If confirmed, boating season may have been out after all, but there would have been plenty of space to put some ice skates to good use.

Based on data from multiple satellites orbiting Mars, scientists have found many traces of flowing water across the Martian landscape. Many fed into what would have been enormous lakes, ranging from the size of Lake Tahoe to a location called Heart Lake, which would have surpassed Lake Erie. While many valleys and river patterns have been previously noted on Mars, these new features stand out for their relative youth. At points were they intersect with impact craters from meteors, the apparent riverbeds cut through the craters, rather than get obscured and covered by them. This would require that the water flowed after the crater was formed, giving us a reference point for the water’s age.

Not warm enough for water?

Based on when those craters would have been created, we can then presume that there was some form of water moving on Mars no more than three billion years ago. This stands out, because it would indicate that water was flowing after Mars had lost most of its atmosphere, around 3.7 billion years ago. Without any kind of atmospheric greenhouse effect, the planet’s surface temperatures dropped considerably, generally to  the range of -67° Fahrenheit.

These frosty temperatures might seem like they would prevent any kind of water flow, and while it was a surprise, this hypothesis is actually supported by the size and shape of some of these geological features. Compared to rushing rivers that tend to cut deeply into rock via erosion, these cold, Martian streams and lakes were relatively smooth and shallow, matching what you might expect from trickling runoff as it dribbled across (or under) ice and snow. The source of heat to cause a bit of melting remains to be seen, but a shift in Mars’ tilt may have boosted sun exposure just enough to get things moving.

Source: Huge Mars Lakes Formed Much More Recently Than Thought by Mike Wall, Space.com

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