Lava Tube as Habitats on Mars

A small base on Mars. During early period of exploration and settlement, lava tubes and caves on Mars may provide necessary radiation protection thus minimising engineering and logistical challenges of establishing early outposts on the red planet.

Lava caves and tunnels on Mars

Mars is a frigid, cold and geologically 'dead' world. But even the very first look of the planet reveals structures such as extinct volcanoes and lava flow channels, telling a different story from its untold past. Mars is home to the largest volcanoes that ever existed anywhere in the Solar System. The monstrous volcanoes of the Tharsis bulge were active until up to nearly 3 billion years ago, regularly spewing lava and growing to enormous sizes owing to the lack of plate tectonics and lower gravity compared to that of Earth. The slopes of these volcanoes and the surrounding plains have numerous lava flow channels on the surface and beneath it, many of which are manifested by collapsed roof forming pit craters. These lava flow channels are much larger in diameter than that on Earth, and much greater in length, ranging from few kilometers to several hundred kilometers owing to lower gravity and comparatively less compact surface.

What a lava tube might have looked like during the era of active basaltic volcanism on Mars more than 3 billion years ago.

Importance in habitation prospects on Mars

The thin atmosphere and an absence of magnetic field means the Martian surface is constantly bombarded with an onslaught  of all types of radiation the cosmos throws at it, including the solar UV radiation, solar wind, and the most dreaded of all - the Galactic Cosmic Radiation (GCR) consisting of very high energy protons (0.1GeV to 1GeV or even higher).

Surface habitation of humans on Mars for extended periods is not possible without mitigating this radiation problem. Many surface habitat concepts propose several meters thick regolith or water shield to absorb much or all of this radiation, or deployment of a cryogenically cooled superconductor powered radiation shield (e.g. AIRS by Mareekh Dynamics). Living underground is another option. However, the artificially bored tunnels may be cramped and narrow, making comfortable living impossible.

Subsurface lava tubes and caves have been considered a viable alternative in many different habitation models for Mars. Not only are these naturally excavated, they are also much wider and roomier than artificially bored tunnels, ranging from several hundred meters in width, and hundreds of kilometers in length. Lying only a few meters underground, these tunnels are also quite accessible as many have sections of roof caved in at places opening portals of entry and natural sunlight.

Unlike limestone caves on Earth, most of these lava tubes are superficial and level, as their floors are formed by cooling of fluid lava, giving an added advantage of underground spaces with flat floors.

During early stages of human settlement on Mars, these lava tubes may provide a sanctuary for early settlers to build or deploy small pressurized habitats protected from most of the solar and cosmic radiation. They also can provide closer and relatively direct access to the subsurface water ice which is abundant in many regions on Mars at mid to high latitudes.

Prospect of lava tubes in Craterhab technology

Our patented pressurized habitat system - the Craterhab - is designed for large scale surface living on planet Mars. The radiation protection comes from our proprietary on-demand powered radiation shield, the Active Integrated Radiation Shield (AIRS). The shield utilizes high-temperature (-180c) superconducting YBCO cables cryocooled by liquid nitrogen flowing through a single cable unit. The flow of electricity through the YBCO cable cooled down to -196c will create an electromagnetic radiation shield effective over tens of meters around it.

Construction of such cables on Mars will require a manufacturing unit which is impossible to construct on Mars during the early establishment of a Martian base. Early Craterhabs will be focused more on immediate survival through pressurization of smaller sized 30-50m diameter habitable spaces, paving way to ever larger domes through the use of this highly scalable habitation technology. Therefore, creating a powered radiation shield may not be feasible during the early stages.

To protect the early humans on Mars from radiation, and give them a safer environment while providing a relatively easy access to basic resources such as the subsurface ice, it would be ideal to establish the earliest Craterhab base inside the lava caves and tubes. The several meters thick layer of naturally formed regolith roof, compacted through heat and gravity will provide a much safer environment free of radiation for small early stage Cratehabs.

Choice of location

Lava caves and tunnels on Mars are more common along the slopes of the extinct volcanoes, spanning several hundred kilometers. The location of many of these caves is revealed through the pit craters formed due to the roof collapse in several sections along the caves, but there could be many more with more stable and intact roofs. One can locate the path of these lava cave systems through imagery of space probes and satellites orbiting Mars such as Mars Odyssey, MRO and Mars Express among many others. 

One of my personal favourite locations for a future Craterhab base is the eastern flanks of Alba Mons or Alba Patera - an ancient volcano - which is by far the largest single volcanic feature on Mars, even larger than the tallest volcano in the Solar System, the famous Olympus Mons. Alba Patera is extremely flat, a mere 0.5 degree slope up towards its caldera. One of the reasons for it being flatter and wider is its formation by very thin lava, like a thin pancake batter, resulting in flatter topography. This may have led to the formation of the finest and largest lava caves on the red planet. 

There are numerous lava tubes and clusters of impact craters in close proximity along the Eastern flanks of the Alba Mons, offering a perfect venue for future lava cave and surface Craterhab bases on Mars.

Advantages of lava caves

Size

In contrast to the artificially bored tunnels, lava caves and tunnels of Mars are not only much wider and roomier, they are much longer as well, stretching hundreds of kilometres along the slopes of these volcanoes. 

Flat topography

These lava tubes are formed on relatively flat surfaces, which is well suited for early settlement construction and the ease of travelling around.

Access to resources

These lava tubes provide access to the most needed resource on Mars in the early stage; water! The water on Mars is in the form of subsurface ice (permafrost or glaciers) very close to the surface and is several meters to up to 8km thick. This water can be tapped from these cave walls and processed for consumption and manufacture. There could be access to other necessary minerals hard to detect from surface or orbital instruments, including volatiles.

Protection from radiation

Radiation exposure on Mars is 300 - 1000 times more than that on Earth. Nearly 80-95% of this is Galactic Cosmic Radiation (GCR), consisting of 0.1GeV to 1GeV particles which have a high penetrance and, unless a novel powered shield could be developed, will require protection in the form of several meters of material shielding (regolith or water), which carries immense engineering and logistical challenges.

Lava tubes on Mars are under several meters thick layer of Martian soil, hardened by the heating and melting process of the underlying flowing lava. This thickness is sufficient to block the radiation from penetrating the interior of the cave or tunnel. This forms an ideal environment to establish an early human base inside a lava tube.

Protection against meteors

Being several meters thick, the roof of a lava tube will offer excellent protection against the meteors capable of puncturing and damaging the habitats and harming the occupants.

Early Craterhabs will be relatively small, perhaps 20-30m in diameter. Any impact from a meteorite will have the potential for rapid depressurization, giving only a few minutes of response time to either repair the leak, or take protecting measures such as donning a pressurized EVA suit, or retracting inside a pressurized emergency pod. Building such Craterhabs inside the lava tubes will protect against such potential accidents. Once infrastructure and capabilities have been developed to manufacture and install much larger habitats such as 50-500m diameter Craterhabs on the surface, their sheer volumes will provide safety against rapid depressurization from potential meteorite hits by giving tens of minutes to hours of response time for repair and take protective manoeuvres.

Temperature changes

The daytime temperature on Mars can be several degrees above zero during high noon in lower latitudes closer to the equator. But the temperatures can rapidly drop to minus 100c or below with the nightfall. For early smaller habitats, this drop in outside temperature will cause rapid loss of radiant heat from its surface. Building such habitats in the lava tubes will protect against rapid decline in temperature and help save power in maintaining the internal heating and temperature.