Get talking – Materials that could bring life to Mars

Materials World magazine
,
2 Apr 2020

Samir Jaber, engineering content writer at materials search engine Matmatch, describes how testing could make or break life on Mars.

Human colonies on Mars have long been the stuff of sci-fi. Today, such concepts are becoming possibilities with better understanding of the resources available on the red planet. It is not feasible to transport all the materials that humans need to live, subsist and remain safe on Mars over the long-term. Instead, engineers would have to turn to Mars’ indigenous resources. Fortunately, the red planet’s natural resources, and their possibility to foster human life, are central to why notions of populating Mars have moved from fantasy to scientific plausibility. 

For one thing, Mars has carbon that can be extracted from the atmosphere and used to make plastics, rocket fuel or heating fuel. Nitrogen, hydrogen and oxygen are all biologically accessible in forms like carbon dioxide gas, nitrogen gas, water, ice and permafrost. In situ resource utilisation (ISRU) equipment could be key to exploiting these resources, like subsurface water ice deposits.

Building a new society 

As for building materials, Mars’ settlers will not be short of ceramics thanks to the ubiquity of clay-like materials. There are also plentiful mineral resources including iron, titanium, nickel, aluminium, sulphur, chlorine and calcium. 

Silicon dioxide is the most common material on Mars, according to Viking space probe measurements, and is also a basic ingredient of glass. It is likely that glass products – including fiberglass – and structures could be constructed on Mars in much the same way as they are on Earth. Regolith is another readily available Martian construction material. The pulverised, dusty rock — mostly silicon dioxide and ferric oxide, with aluminium oxide, calcium oxide and sulphur oxide — has been deposited over Mars by asteroid collisions over billions of years. Researchers think that regolith could be a viable alternative 
for concrete.
 
Samples have yet to be brought back to Earth. Instead, JSC Mars-1a, a regolith simulant, is a very close replica of Martian soil. JSC Mars-1a has been used to explore the possibility of using regolith in 3D printing. 

But how strong would Martian concrete be? Mars has a lot of sulphur in its soil, and molten sulphur is used to bind some concrete on Earth. Tests at Northwestern University, Illinois, USA, have mixed  melted sulphur with JSC Mars-1a in a ratio of 1:3, the same recipe used for sulphur concrete on Earth. Tests of the simulated Martian concrete’s strength under compression, bending and splitting found it to be much weaker compared with concrete made using Earth sand. This was attributed to the porosity differences. The Earth composition’s compression strength was about 30MPa, similar to that of cement-based concrete. 

Further experiments with a 1:1 sulphur-to-sand ratio compressed the mixture, broke down grains and drove out air bubbles. This resulted in a strength of 60MPa, which is twice as strong as concrete. Sulphur-based concrete also has quick-setting advantages, offering more immediate strength that could be advantageous for 3D printing applications. 

Aside from cement, modular underground living will likely be the surest way to protect Mars’ settlers from cosmic radiation and intense cold. Such digging could also expose water, ice and other resources under the surface for ISRU. However, NASA’s plans to send a manned three-year mission to Mars in the 2030s can only happen if the astronauts have a continual food supply. This is where aerogel might help – a synthetic porous ultralight material. Specifically, silica aerogel — the most common type of aerogel - is a good insulator and a poor conductor of heat. 

If silica aerogel shields were placed over sufficiently icy regions of Mars’ surface, then photosynthetic life could survive with minimal subsequent interference. Mars’ colonists would then have the capability to grow their own food.


Testing, testing…


Ongoing tests include those by the University of California in San Diego, USA. Here, researchers are examining the relatively high concentrations of perchlorate compounds, containing chlorine, in Martian soil, rendering it toxic. The studies aim to assess whether the perchlorates change material behaviour. They may offer a potential energy source for microorganisms and therefore potential to grow life. 


Other studies, such as at the UK Centre for Astrobiology at the University of Edinburgh, Scotland, are less positive about perchlorates. One test exposed cells of the bacterium – Bacillus subtilis, a common spacecraft contaminant  – to perchlorates and UV radiation at levels similar to those on or near Mars’ surface. The cells lost viability within minutes, and even more quickly in Mars-like conditions - and their lifespan decreased to 60 seconds when iron oxides and hydrogen peroxide, two other common components of Martian regolith, were added to the mix. The data concluded that the probable survival of biological contaminants on Mars’ surface is low. 


It is clear that Mars’ resources offer much potential in supporting human colonisation. But it will fall to engineers to ensure that the fruits of these opportunities are safe, realistic, ethical and long-term. While colonising Mars seems less like science fiction, rigorous materials testing on Earth will be crucial in determining whether humanity, and its design and civil engineers, can lay the foundations for human life on Mars.