INTERPRETING PHOSPHATE MOBILITY IN EARLY, POTENTIALLY HABITABLE ENVIRONMENTS ON MARS

Phosphorus is a critical nutrient for life, important in DNA, RNA, ATP, and phospholipid membranes. In addition, phosphorus, either as phosphate or a more reduced species, was likely important in the prebiotic reactions leading to life. Low phosphate concentrations and reactivity are considered the “phosphate problem” that may have faced the origin of life on Earth, and potentially also on Mars. In order to better understand phosphate mobility in early, potentially habitable environments on Mars, we have performed experiments, modeling, and field work in Mars-analog environments.

Dissolution of the dominant primary phosphate-bearing minerals in martian meteorites, Cl-bearing apatite, and merrillite, result in faster dissolution rates and higher equilibrium concentrations of phosphate for both minerals compared to the dominant terrestrial primary phosphate-bearing mineral, fluorapatite. This suggests that the phosphate concentrations of early martian environments may have been more than twice those of Earth, with P release rates from aqueous interactions with more P-rich rocks on Mars > 45 x those on Earth.

In acidic low temperature environments, amorphous Al- and Fe-phosphates are likely to form from weathering of primary phosphate minerals. Therefore, in order to help interpret phosphate release in such environments, we synthesized amorphous Al- and Fe-phosphates, and dissolved them in flow-through reactors. Results indicate increased phosphate release from amorphous Al-phosphates relative to the crystalline Al-phosphate variscite, suggesting enhanced phosphate release in such environments.

These results have significant implications for the origin and persistence of life on Mars, suggesting that the “phosphate problem” that potentially challenged the evolution of life on Earth could be less important on Mars. Additional work is ongoing to further interpret phosphate availability in early, potentially habitable environments on Mars.