Challenging the agricultural viability of martian regolith simulants

As human space exploration extends farther from Earth, the cost and risk of resupplying a mission increases substantially. In situ resource utilization (ISRU) is the prospecting, extraction, storage, and exploitation of existing resources at the crew location, reducing cost and risk. Crucial to the development of ISRU solutions is the accurate characterization and modeling of regolith for a variety of applications, including as a substrate for food production at lunar or Martian sites. Previous studies have established the capacity of specific regolith simulants to support the growth of a variety of plants in the short term. However, the mineralogical and physical accuracy of these simulants as proxies for the sites on Mars is debatable, and any conclusion drawn from studies with these simulants must be considered with some degree of caution. For the purpose of studying ISRU food production, we present a systematic effort to evaluate the utility of three different Martian Regolith Simulants (MRSs): JSC-Mars1A, Mars Mojave simulant (MMS), and Mars Global simulant (MGS-1). Our findings confirmed that none of these simulants are capable of supporting plant growth in the absence of nutrient supplementation. However, with the addition of a nutrient supplement, both JSC-Mars-1A and MMS were able to support the growth of both Arabidopsis thaliana and Lactuca saliva. However, the highly alkaline (pH > 9.0) MGS-1 simulant was unable to support growth even with additional nutrients. Acidification of MGS-1 nearly doubled the longevity of plants grown in this medium, suggesting this simulant may be further modified to eventually support plant growth as well. The addition of calcium perchlorate to each simulant, at concentrations intended to mimic those observed on the surface of Mars, rendered each simulant incapable of supporting plant growth, regardless of nutrient supplementation. These findings underscore that ISRU food solutions are likely at a lower technological readiness level than previously thought. We discuss these findings in the context of future efforts to develop off-world agricultural systems, approaches to developing future MRSs, and the immediate need to address perchlorate contamination as well as nitrogen deficiency for regolith-based food production.