It might not look like much from space, but this depression in the Martian landscape might be considered to be a priceless feature when viewed by future Mars colonists.
In December 2008, the Mars Reconnaissance Orbiter (MRO) flew silently over the Tharsis bulge, the location of a series of ancient volcanoes. The High Resolution Imaging Science Experiment (HiRISE) captured what appears to be a deep hole. This kind of feature has been seen before, like a Martian pore, deep and foreboding. Usually these sinkholes aren’t as deep as they look, but they are deeper than the surrounding landscape. They are also similar to their terrestrial counterparts in that they have very steep sides (unlike the gentle, eroded slopes of crater rims) and they are caused by a lack of material below. On Earth, sinkholes often form due to water flowing beneath, removing material, causing the overlying rock/soil to slump, forming a sudden hole. In the example above, the sinkhole (or “collapse pit”) was caused by tectonic activity. In this case, it is likely that the material dropped into a void left over by magma-filled dykes (lava tubes from old volcanoes).
The result is a hole with very steep sides. It has been suggested that these sink holes may be useful to future Mars colonists, as they can use the natural feature for shelter. On Mars, humans would be subject to an increased dosage of radiation (due to the tenuous Martian atmosphere and lack of a global magnetic field), so it is preferable to find any form of natural shelter to build your habitat. The depth of this kind of sinkhole will afford some protection, and drilling into the cavern side would be even better. Perhaps even put a dome over the top? No need to build walls around your building then. Also, there’s the interesting–if a little frightening–prospect of accessing underground lava tubes. Therefore, colonists won’t need to dig very far to create a subterranean habitat with all the radiation protection they’ll ever need (the insulation would also be impressive).
Although this scenario might be a little far-fetched, and probably only suitable for an established human presence on Mars (after all, the numerous valleys would probably suffice for most permanent habitats drilled into cliff faces), it does go to show that the current missions in orbit around Mars are doing a great job at seeking out some possible housing solutions for our future Mars settlers…