The caves of Mars are the environment about which the least is known, due to their low accessibility. Most underground chambers lie deep beneath the ice pockets and permafrost, where insulation and geothermal heat allow sections of ice to melt up to form hollow, flooded caverns. Most of these have so far only been explored with robotic probes, with meagre results. More accessible are hollow lava tubes. Lava tubes form during eruptions, when rivers of molten rock eat their way through the mountain slopes and plains. The surface of these rivers can harden before the the rest does, forming a solid roof underneath while the still liquid lava flows away, leaving behind a hollow tube. Once cooled down, water and life may seep into these caverns. The roofs of ancient lava tubes are prone to collapsing and thus have many openings to the outside world, making for adequate shelters for mountainous life.
Fig. 2: Outside view of a massive sinkhole into a cave system formed by lava tubes. Unfortunately, giant sandworms have not been found on Mars (yet).
Life in the underground comes with advantages and disadvantages. It is usually warmer and wetter than on the surface and one is greatly shielded from dust storms and radiation. On the flipside, the lack of sunlight forces animals to adapt their sensory organs to unusual degrees and limits the energy available to the primary producers to anaerobic pathways.
Despite the lack of photosynthesis, oxygen-levels comparable to those on the surface have been found in a handful of quite deep caverns. These oxygenated caves are usually close to perchlorate deserts, so there is a possibility that the oxygen in them stems from perchloratovorous areonts.
Image Sources:
- Fig. 2: HiRISE
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