The 35-meter wide hole in the image taken from the camera on the Mars Reconnaissance is a geological mystery waiting for future exploration by spacecraft, robots, and astronauts. Photographed in 2011 by the HiRISE instrument on the Mars Reconnaissance orbiter, this unusual feature on Pavonis Mons, a large shield volcano in the Tharsis region, appeared to be the entrance to a massive underground cave. Further analysis revealed that the crater is 35 meters in diameter, and the cave below is about 20 meters deep, likely having been 90 meters deep before collapsing and filling, according to IFL Science.
The cause of this hole is a geological mystery, as caves of this size on Earth are usually created by water dissolving limestone and are most common in karst terrain. This terrain consists of rocks below ground that can be dissolved by flowing groundwater, including limestone and other carbonate rocks. When the topsoil collapses into the cave, it creates a sinkhole. However, Mars has no signs of carbonate rocks like limestone and very little water.
A more likely explanation for the giant hole on Mars is that it led to a lava tube. Lava tubes can form when the top layer of a lava flow hardens above ground while the lava continues to flow underground in a pipe. The collapse of sections of the roof can create holes as seen in orbital images. These types of holes are of interest to NASA as the caves below are relatively protected from Mars’ harsh surface, making them potential locations to harbor Martian life. Plans for future exploration involve using spacecraft, robots, and astronauts to investigate further.