Scientists are puzzling over an almost perfectly circular pit on the surface of Mars.
NASA's Mars Reconnaissance Orbiter has spotted another intriguing formation on the planet's barren surface.
The spacecraft captured the image of a remarkably circular pit - and what its dark, yawning entrance leads to is, according to Futurism, a question high on the minds of Mars scientists.
The image, "acquired to determine if any underlying void ... and associated faults" were in the region, was taken with the High-Resolution Imaging Science Experiment (HiRISE) camera, a powerful lens capable of detailing the Martian surface in both visible and near-infrared light.
Nicknamed "the little pit," the formation only measures a few yards across, according to the HiRISE lab, and sits in the shadow of the Arsia Mons, a volcano that is over 270 miles in diameter and stands at nearly 12 miles tall (one of the largest known in the entire solar system).
But despite their best efforts, scientists can only guess as to how exactly holes like this one were formed, or what may be lurking in their depths - let alone whether they could make for a suitable shelter for future astronauts.
As this pit was found in a region of historic volcanic activity, the best current guess is that it leads to a network of lava tubes, underground channels where molten rock once tunnelled its way through the planet. Taking that a step further, some research has shown that these tubes could house a long-term base on the planet, where astronauts would be shielded from harsh cosmic radiation.