On the scarred terrain of Arabia Terra, a region on Mars that serves as the setting for The Martian, lies a mysterious pockmark known as Ismenia Patera. New imagery released by the European Space Agency (ESA) on Thursday reveals dimensions of this feature that help contextualize its geological evolution (though its origins remain unresolved).
With a diameter of about 47 miles (75 kilometers), the depression is one of many pateras—the term for flat bowl-shaped indents on terrestrial worlds—in this neck of the Martian northern hemisphere. Arabia Terra is thought to be one of the oldest landscapes on the red planet, with some segments dating back nearly four billion years, so these features are important in understanding the planet’s distant past.
Given its large size and hints of ancient ejecta, Ismenia Patera is clearly the result of some spectacularly catastrophic event, but scientists aren’t exactly sure what that blast might have been. One explanation is that the hole is a crater left behind by a meteorite impact, while another posits that Ismenia Patera was the site of a supervolcano that spewed out such ridiculous amounts of magma that it collapsed in on itself, and died.
The above topographic view, captured in January by ESA’s Mars Express orbiter, outlines the complicated matrix of dips, gullies, and smaller peaks within the patera itself. If the depression was blasted out by an impacting space rock, these interior features may have formed as ice and sediment streamed into the crater, causing visible fissures. If the patera was created by a self-destructing supervolcano, the cracked structures may be the remnants of the eruption as it collapsed.
Read More: What Are These Blue Spots on Mars?
Even though Mars Express is getting a fancy new software upgrade next week, it probably won’t be able to resolve the dilemma of Ismenia Patera’s origins. That will have to be investigated on the surface by future landers or rovers—or eventually, real-life versions of the interplanetary explorers in The Martian.
Get six of our favorite Motherboard stories every day by signing up for our newsletter.