Mars Had Liquid Water On Its Surface. Here's Why Scientists Think It Vanished

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A new study indicates that the relatively low mass of Mars allowed most of its water to be lost to space billions of years ago, rather than retained on its surface.
Mars Had Liquid Water On Its Surface. Here's Why Scientists Think It Vanished

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All evidence points to the fact that Mars once had flowing water, but numerous flybys, orbiters, landers and rovers have confirmed one undeniable fact — any liquid water that was once on its surface is now long gone.

A study out of Washington University in St. Louis might have found the reason: Mars, which is about half the size of Earth, and just over one-tenth the mass of our own watery world, might just be too small.

One idea, the Mars Ocean Hypothesis, suggests that Mars not only had some liquid water, but a lot of it. But the new study's co-author Kun Wang says his team's finding, which was published this week in the Proceedings of the National Academy of Sciences, pours cold water on that notion.

"Mars' fate was decided from the beginning," Wang, an assistant professor of Earth and planetary sciences, said in a statement. "There is likely a threshold on the size requirements of rocky planets to retain enough water to enable habitability and plate tectonics."

That's because the lower mass and gravity of Mars makes it easier for volatile elements and compounds such as water to escape from its surface into space.

Led by Zhen Tian, a graduate…
Scott Neuman
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