What causes Europa's mysterious "chaos terrain"?

Put in plain language, astrophysicists have figured out why Jupiter's moon Europa looks so fucked up. The frozen moon's surface is a layer of solid ice over a liquid sea — and that ice is shattered, cracked, broken, sunken, and twisted into contortions that science can't fully explain. But now a new study suggests one simple source of the Europan landscape that's so distorted it's called "chaos terrain."

There are few features in the solar system like Europa's Thera Macula, a region where the frozen skin of the moon has sagged into a valley full of weird bulges and huge blocks of ice. To understand what natural processes could cause such landscape insanity, a group of researchers studied similar structures in the glaciers of Iceland and Antarctica. What they learned was that glaciers are far from solid blocks of ice. They are riven by fractures, and often contain highly-pressurized ponds of water inside them. Because these ponds are usually trapped between two layers of ice, they are distorted into a lens shape — the researchers call them "melt lenses."


Melt lenses are basically lakes locked within the ice. And on Europa, they are often vast, and could stay liquid for centuries, warmed by the moon's underwater volcanoes. In a paper published today in Nature, the scientists write, "The sunken topography of Thera Macula indicates that Europa is actively resurfacing over a lens comparable in volume to the Great Lakes in North America." In this diagram from their paper, you can see that the researchers propose one theory about how Thera Macula formed. First a melt lens pushed the ice up, then it sank as the lens was distorted by pressure. Later, the lens collapsed entirely — the water flowed away through cracks, and the surface of the ice calved into big chunks floating in a briney slush.

Later, the lens finally froze, expanding as it did so. It pushed the chunks of ice to the surface, and squeezed that brine upward into bizarre-looking bulges. It's an ingenious solution to a problem that many have wondered about — including, famously, Arthur C. Clarke, whose aliens in 2010 inform humanity that all the worlds in the solar system are ours "except Europa." Because the chaos terrain is so bizarre, it suggests subsurface structures like cities or farms created by some kind of thriving civilization beneath the ice.


Though melt lenses may not be as exciting as subglacial alien neighborhoods, there's still something pretty badass about the idea of the Great Lakes entirely encased within kilometers of ice, crushing and distorting the landscape from below.

You can read the full scientific paper, "Active formation of ‘chaos terrain' over shallow subsurface water on Europa," in Nature.


Images of Europa via NASA

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