This 'Crater' Might Actually Be an Ancient Martian Supervolcano

A crater on the northern face of Mars could be hiding a violent history. New images from the European Space Agency (ESA) provide more evidence that the crater might actually be the site of an ancient martian supervolcano.

On Thursday, ESA released a new set of high res images from its Mars Express mission, a probe currently orbiting the Red Planet to study its geology, atmosphere, and climate. Among the set was a nice crisp shot of Siloe Patera, a geological formation of two large craters—one inside the other—in the Arabia Terra region on Mars. It's a huge formation: almost 25 miles across at its widest point and more than one mile deep at its deepest, but some astronomers believe it may not be a crater at all. These images provide a few more clues that it might in fact be the collapsed center of a supervolcano.

A supervolcano is a volcano that can produce at least 1,000 cubic kilometers of volcanic ejecta in a single eruption. By comparison, the 1980 Mount St. Helens eruption that killed 57 people produced about 1.25 cubic km of ejecta. So yeah, supervolcanoes are pretty massive.

But because they're so intense, it makes it hard to identify them millions of years later, ESA explained in a blog post about the new images. Rather than the classic mountain-shape that comes from multiple milder eruptions, supervolcanoes just kind of explode, destroying everything around them, include themselves.

There are several features near Siloe Patera that astronomers believe are possible calderas, the term for a collapsed volcano center. A 2013 article published in Nature outlined certain geomorphic features of martian craters that indicate they are likely supervolcano calderas, including ridged plains and channels coming out of the edges.

By comparing Siloe Patera to other craters and to calderas on Earth, it seems very likely that this structure is in fact the lingering thumbprint of an ancient martian supervolcano. For one, as ESA points out, it has steep-sided walls and channels snaking out from the edges (where volcanic material would have run). It's also lacking a lot of the characteristic features of a crater, like a central peak and a pronounced crater rim.

"Arabia Terra is already known to comprise plains of fine-grained, layered sulphate- and clay-bearing materials," ESA wrote. "The source of the material has been much debated, but lava and dust from eruptions could be the explanation."

Like all good scientists, ESA astronomers aren't ready to declare Siloe Patera a supervolcano caldera until they have some conclusive evidence gleaned from more data and even more detailed imaging. For now, these high-res images and the distinct possibility of an ancient martian landscape erupting with climate-altering explosions certainly spark the imagination.