Alex Tolley follows up his analysis of agriculture on Mars with a closer look at the Interstellar Research Group’s MaRMIE project – the Martian Regolith Microbiome Inoculation Experiment. Growing out of discussions on methods beyond hydroponics to make the Red Planet fertile, the project is developing an experimental framework, as described below, to test our assumptions about Martian regolith here on Earth. A path forward through simulation and experiment could help us narrow the options for what may be possible for future colonists. Fertile regolith, achieved through perchlorate removal, would open up possibilities far beyond what is achievable through hydroponics.

by Alex Tolley

Successful settlement of distant locations requires living off the land, which requires resourcing food. Failure can lead to disaster, as experienced by some of the early American colonies. While near Earth space settlements could be supplied with packaged food, this would be too costly for an expanding Mars base over the long term. Food and air must be supplied from local sources, a point that has been emphasized by the Mars Society’s president, Robert Zubrin (Zubrin, 2011).

In the mid-20th century, it was assumed that agriculture on Mars would be like that on Earth, with crops growing in the Martian soil, but under clear domes to maintain air pressure, and light for photosynthesis. As a result, the focus for settlement was on the shiny technologies of transport and the design of Martian bases and cities.

Image: The Martian Base: Painting for The Exploration of Space by Arthur C Clarke. Credit: Leslie Carr.

This rosy picture of farming on Mars was disturbed after the Apollo missions when it became apparent that plants did not grow well in lunar regolith samples. The Phoenix lander’s discovery of perchlorates on the surface of Mars meant that the Martian regolith would be toxic to plant growth without remediation. Perchlorates are found on Earth, for example in the Atacama desert, but in far lower concentrations than the 0.5-1.0% concentrations found on the surface of Mars. Perchlorates are used in industry, and the US EPA regulates perchlorate contamination because of its toxicity.

Because of the adverse nature of regolith on plant growth, the focus shifted to soilless agriculture using hydroponics or aquaponics, but as we saw in the previous post, there are limitations on the use of hydroponics. Plants with extensive root systems needed for support, especially trees, can’t be grown this way, eliminating the availability of tree fruits and nuts. Most of our grains cannot be grown using current hydroponic methods either. It really would be useful if the regolith could be altered to make it suitable for traditional agriculture, perhaps more like the farms in arid areas, such as the Middle East.

In 2022, after participating in a panel discussion on establishing a sustainable human presence on Mars at a science fiction convention (LibertyCon) in Tennessee, members of the Interstellar Research Group (IRG) including Doug Loss, Joe Meany, and Jeff Greason, considered how some experiments could be done to test how best the regolith might be treated to remove the perchlorates with bioremediation using bacteria, and convert the sterile regolith into soil suitable for agriculture. Some species of bacteria metabolize chlorates and perchlorates for energy, and therefore could be used to remediate the regolith. Relatively small, low mass cultures could be brought from Earth and exponentially cultured to meet the requirements for the volumes of regolith to be treated.

Bioremediation of perchlorate contaminated soils is established practice (Hatzinger 2005), suggesting that if it could be adapted to Martian conditions, this may be a viable solution to remove the perchlorates and solve the toxicity issue.

This use of bacteria, a low mass approach to remediate the regolith was the inspiration for core IRG members to propose a project, the Martian Regolith Microbiome Inoculation Experiment.(MaRMIE).

Mars is almost certainly too dry and cold to just irrigate the regolith on the exposed Martian surface with an inoculant of perchlorate metabolizing organisms. Knowledge about the required conditions for successful large scale regolith bioremediation, especially of temperature and pressure, was required, as well as the issue of UV and ionizing radiation.

Simulating the Martian Surface

The initial idea was to run experiments in a sealed chamber that mimicked the Martian surface environment to determine whether a terrestrial type soil might be created in which agriculture could be practiced. This Mars simulation chamber would contain a Martian regolith simulant (MRS) with added perchlorate, and inoculated with suitable bacteria. If the bacteria could break down the perchlorate, it would indicate that this approach could, in principle, be used to remediate the regolith from the surrounding area, which would then be used inside a greenhouse to grow the food crops. By doing so, the mass, complexity, and likely equipment failures of a hydroponic system could be avoided, and a more traditional agricultural approach could be practiced. This was a far more scalable solution than a technical one, allowing food production anywhere it would be needed, and was in much closer alignment with ISRU.

Early thinking was to design the experiment and have an outside PI with expertise and funding to refine the design and run the experiments. The IRG would publish a review article, and at some point participate in writing a paper on the results.

At this point, the initial group decided to invite others who might be interested in providing input and expertise to investigate the biological remediation of regolith. Of particular importance was the need to design experiments that could be done at suitable facilities. IRG hopes the guidelines that develop out of this work may be of use to anyone pursuing research into agriculture for future use on Mars, and offers them to any organization that chooses to draw on them.

Prior work had identified various bacteria that had the genes that encoded the enzymes to reduce the [per]chlorate and extract energy from it (Balk 2008, Bender 2005, Coates 2004). As the genes coding for the various enzymes for perchlorate metabolism were known it has been suggested that by just liberating the oxygen from the perchlorate the regolith could be a useful source of life support and rocket fuel oxidant (Davil 2013), therefore offering another avenue of ISRU using an engineered bacterium.

Will bioremediation need to be taken inside the base, and if so, can or should it be done as close to Martian conditions as possible, or should it be done as close to the living or working conditions, and plant growing conditions in the agricultural greenhouse? Would it be better to grow the bacteria in a bioreactor rather than in situ, or even extract the enzymes to treat the regolith, thus controlling the bacteria growth and both reducing the perchlorates and liberating the oxygen as a useful side product?

These questions can only be answered with experiments testing the various bacterial inoculants under varying conditions from terrestrial to Martian, as well as applying economic and other analyses to determine the more effective way to use bioremediation on the regolith as an initial step to making it a proactive soil for farming.

While bioremediation is one approach to removing perchlorates, the fact that they are readily water-soluble suggests that if free water is available, the regolith could be simply washed to flush out the perchlorates. This would require more plant to wash the regolith and then remove the salts to recycle the water. This method would work more effectively on regolith than soil and would not require the controlled conditions of bacterial growth and the time to build the culture.

The Phoenix lander detected the perchlorates as they deliquesced on exposure. Experiments have shown that the perchlorates will deliquesce under Martian conditions (Slank 2022).

Removal of the toxic perchlorates is just the start of the process to make the regolith fertile. There have been a number of experiments with regolith simulant to grow a variety of plants and crops under terrestrial conditions of temperature and pressure, the sort of conditions that might be expected in a Mars greenhouse that has humans managing the farm.

By far the best results have been achieved by increasing the illumination to terrestrial levels and adding carbon-rich soils to the regolith, which now will also include the many soil organisms that improve the soils. A partial solution that has also worked is to grow cover crops like alfalfa grass or reuse the waste from prior crops to be added into the regolith to improve its water retention and nutrient supply. (Kasiviswanathan 2022).

So far none of these crop growing experiments have been attempted at pressures and temperatures that differ from optimal terrestrial conditions. There is considerable space to repeat these experiments under different conditions, especially if it proves important to build structurally lighter greenhouses, or even use artificial illumination in below-ground farms, much like container farming today. While oxygen can be extracted from Martian air, water and rocks, nitrogen is less readily available, as is phosphorus. These macronutrients and the other micronutrients will have to be found and extracted to support plant growth whatever farming method is used.

As a result of all these questions, the MaRMIE project has expanded in scope beyond bioremediation, to include crop growth experiments under non-terrestrial conditions.

An Experimental Framework

The project has generated an outline of the experiments that might be done, starting with bioremediation, and extending out into the more general issue of agriculture under conditions that differ from terrestrial ones. Even this is the tip of the iceberg as gene engineered organisms might well be better adapted to conditions on Mars, reducing containment costs, nutrients, and allowing faster scale-up to support an expanding settlement.

The experimental framework encompassing the ideas to date has 4 phases:

1. Remediating perchlorates in the regolith, and any problematic chemicals produced as a result of the remediation. This requires acquiring Martian regolith simulants (MRS) and the addition of perchlorates, testing a number of bacterial and microfungal agents to remediate the MRS under terrestrial conditions, and then in stages of pressure and temperature modified towards Martian conditions.

2. Developing a microbiome tailored to Martian conditions with which to inoculate the regolith. The microbiome should lessen or remove tendencies toward cementation of the regolith as well as gradually convert it into actual soil, if possible. “Actual soil” implies the provision of required nutrients for plant growth. This includes testing microbiomes to add to the MRS along with testing pioneer plant species to condition the regolith to become more like soil.

3. Testing plant growth in microbiome-inoculated regolith under Martian lighting levels and atmospheric conditions, gradually increasing the atmospheric pressure until plant growth is acceptable.

4. Continuing plant growth testing per #3, but gradually lowering ambient temperatures toward Martian levels until plant growth diminishes unacceptably.

5. Developing agricultural structures to provide appropriate conditions, with inoculated regolith, lighting levels, atmospheric pressure, and temperature levels previously determined, and with shielding from ionizing radiation.

As for output, the initial idea to publish some sort of review paper on the known issues and prior work, indicating the direction of experimental work needed, is still in process.

As noted at the outset, the IRG cannot execute these experiments and offers this work as a contribution to the field of planetary studies. IRG hopes that this framework will be seen and used as a structure for designing experiments and building on the results of previous experiments, by any researchers interested in the ultimate goal of viable large-scale agriculture on Mars.


Zubrin, R. (2011). The Case for Mars: The Plan to Settle the Red Planet and Why We Must. Free Press.

Kokkinidis, I. (2016) “Agriculture on Other Worlds“

Hatzinger P.B. (2005), “Perchlorate Biodegradation for Water Treatment Biological reactors”, 240A Environmental Science & Technology / June 1, 2005. American Chemical Society.

Balk, M. (2008) “(Per)chlorate Reduction by the Thermophilic Bacterium Moorella perchloratireducens sp. nov., Isolated from Underground Gas Storage” Applied & Environmental Microbiology, Jan. 2008, p. 403–409 Vol. 74, No. 2. doi:10.1128/AEM.01743-07

Bender, K.S, et al, (2005) “Identification, Characterization, and Classification of Genes Encoding Perchlorate Reductase” Journal of Bacteriology, Aug. 2005, p. 5090–5096 Vol. 187, No. 15. doi:10.1128/JB.187.15.5090–5096.2005

Coates J.D., Achenbach, L.A. (2004) “Microbial Perchlorate Reduction: Rocket-Fueled Metabolism”, Nature Reviews | Microbiology Volume 2 | July 2004 | 569. doi:10.1038/nrmicro926

Davila A.F. et al (2013) “Perchlorate on Mars: a chemical hazard and a resource for humans” International Journal of Astrobiology 12 (4): 321–325 (2013). doi:10.1017/S1473550413000189

Slank, R. et al. (2022) “Experimental Constraints on Deliquescence of Calcium Perchlorate Mixed with a Mars Regolith Analog” The Planetary Science Journal, 3:154 (11pp), 2022 July

Kasiviswanathan P, Swanner ED, Halverson LJ, Vijayapalani P (2022) Farming on Mars: Treatment of basaltic regolith soil and briny water simulants sustains plant growth. PLoS ONE. 17(8): e0272209.