The Mars Express orbiter has imaged a series of “pit-chains” near one of the red planet’s largest volcanoes, and these strange surface features may be a potential abode for microbial life.
Pit-chains are circular depressions that are dotted along fractures in the Martian crust, and can have a volcanic origin. When lava flowing from a volcano solidifies into basalt, lava can continue to flow in a tube beneath the surface. The lava flow will eventually cease, leaving the tubes intact. However, eventually part of the roof of these cavities collapse and this results in the circular depressions that form the pit-chains.
The images of the pit-chains were captured on 22 June 2011 in the Tractus Catena region on Mars. This area has a collection of massive volcanoes, such as the three that are collectively called Tharsis Montes, as well as the giant Alba Mons, which is one of the largest in the Solar System.
Pit-chains have also been seen elsewhere in the Solar System. The landing site of Apollo 15, Hadley Rille, had similar features, and on Earth pit-chains flank the Kilauea volcano in Hawaii.
They can also be formed from flowing groundwater, such as found on the Yucatan peninsula in Mexico, when surface limestone collapses to reveal the water underneath.
Pit-chains can also form on Mars if there are strains in the Martian crust. These strains cause a series of parallel elongated depressions, which are called grabens, in which the pit-chains form.
If any cave-like structures associated with pit-chains that were formed from then it is possible that bacteria could have survived in this underground environment.
Even though Mars is further from the Sun than the Earth, it receives around 250 times more harmful radiation at the surface of the planet. This is because Mars lacks any kind of protective magnetic field, and its atmosphere is too fragile to block much radiation. While bacteria have been found in extreme environments on Earth, earning them the name extremophiles, even these hardy bacteria would have a hard time surviving on the Martian surface.
However, caves formed from pit-chains could provide the perfect environment for these kinds of bacteria. Caves could also provide a shelter for any future human explorers to the red planet.
Mars Express is a mission of the European Space Agency (ESA). Launched in June 2003, Mars Express arrived in orbit around the red planet on Christmas Day 2003.