291-2 Exploring the Potential for Radiolytic Ecosystems on Mars

Session: Mineralogy in the Solar System

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The subsurface of planets and moons is the most likely location for life given the general inhospitality of their surfaces. The radiolytic hypothesis posits that natural radioactive decay in rocks splits water, producing oxidants and reductants that support subterranean chemotrophic food webs. We are studying radiolytic ecosystems on Earth and the potential for radiolysis to contribute to habitats in the Martian subsurface.  Radioactive elements are concentrated by a variety of mechanisms, but mobilization of metals in fluid is a necessary step. Past hydrothermal activity on Mars that could have concentrated radionuclides is known from the mineralogic, geologic and geomorphic signatures associated with impact craters and volcanism. Additionally, amagmatic hydrothermal systems associated with radiogenic heat have been proposed (Ojha et al. Nature Comm, 2021, 12:1754).

Data from the Mars Odyssey gamma-ray spectrometer (GRS) reveals three regions where high concentrations of K and Th co-occur on Mars (Isidis, Acidalia, Terra Cimmeria-Sirenum). We examine these locations and their association with alteration minerals identified by CRISM and OMEGA. K and Th are proxies for U and other radiogenic elements and alteration suggests the potential for hydrothermal systems that might concentrate radiogenic material, whether magmatic, impact related, or radiogenic.

The first location is northeast of Isidis Planitia on the margin with Utopia Planitia. Although there are numerous alteration exposures to the northwest and south of Isidis, none overlap with the strongest K and Th signatures. The second location in Acidalia Planitia abuts the strong alteration observed near Mawrth Vallis, but the strongest K and Th signatures are farther north. Only three alteration locations are within the highest radiogenic concentrations, Kunowsky crater and two spots in Acidalia Colles. The third location bridges Terra Cimmeria and Terra Sirenum and spans the Eridania basins. Alteration in this region is abundant and has been previously interpreted as basin floor or hydrothermal seafloor deposits (Adeli et al. 2015, JGR, 120, 1774; Michalski et al. Nature Comm, 2016, 8:15978). This is also the location proposed to have amagmatic radiogenic hydrothermal systems noted above. However, outcrops at the eastern edge (Gorgonum Chaos) and outside the basins have received less attention. The presentation will review these regions and their associations with characteristic alteration types and their potential to host hydrothermal systems that would concentrate radiogenic elements.

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