Investigating the formation of organo-mineral interactions during the first stage of terraforming

The development of a regolith-based bioregenerative agriculture, coupled to an efficient waste management during long-term manned missions to Mars, represents one of the major challenges for space research. This study aims at understanding the mineral weathering and organic matter (OM) turnover in the early stages of terraforming. The Mojave Mars Simulant MMS-1, alone (R100) and with a commercial compost 70:30 v:v (R70C30), was compared to a fluvial sand, alone and with compost (S100 and S70C30). Potato was grown on these substrates for 99 days in greenhouse. Samples were fractionated, obtaining particulate OM (POM) and mineral associated OM (MAOM), and characterized for total nitrogen and organic carbon (OC) and for iron (Fe) K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). In the whole medium, OC increased in S70C30 (10×) and R70C30 (25×). As expected, OC content increased mainly in the POM fraction of both growing media (10× in S70C30 and 20× in R70C30), while OC in the MAOM was 3-times higher in R70C30 than in S70C30. Chlorite, smectite and goethite were the main Fe species in S100, according to XANES, while Fe(III)-OM was found in both fractions of S70C30. Moreover, according to EXAFS, hematite occurred in POM, whereas goethite in MAOM. XANES revealed the occurrence of smectite, maghemite and ferrihydrite in R100, and of nontronite and hematite in the MAOM and POM, respectively. Revealing Fe species involved in the formation of organo-mineral interactions will help improving sustainable space farming.