Enigmatic Issues and Widening Implications of Research on Martian Clay Minerals

Clay minerals are widespread in the Martian crust. Over the last few decades, accumulating data and research into the type, crystallinity, quantity, and distribution of Martian clay minerals (MCMs) has remarkably advanced the understanding of Martian geology, paleoclimate, environment, and the question of whether water, organic matter, and life exist there. Meanwhile, some issues remain enigmatic and arguable. To date, mineralogical data from orbiters and rovers have provided information regarding the distribution, composition, age, and geological evolution of MCMs. Several models for interpreting the formation of MCMs, including weathering, hydrothermal alteration, magmatic precipitation, and diagenesis, have been proposed. Nevertheless, the exact formation mechanism of MCM, remains unclear, primarily because of the lack of sufficient information on the chemical reactions and element cycles involved in the formation of clay minerals. Examination on the type, crystallinity, quantity, and distribution of MCMs indicates that Mars possibly had a warm and wet climate during the Noachian period. Since clay minerals possess abundant -OH groups in the layered structure and can host H2O in the interlayer space, MCMs are thought to be potentially large water reservoirs. Studies of MCMs and their interaction with organic matter are possibly conducive to finding answers to the question of whether or not on Mars life exists as clay minerals can preserve and enrich organic matter, catalyze the formation of biotic molecules, such as RNA oligomers, ribose, and amino acids, and even contribute to the assembly of vesicles. Future missions to Mars are recommended to set studies on MCMs with the key issues above and are expecting to lead to more exciting findings.