44-5 Measuring Sulfur on Mars: APXS, Sulfates and Elemental Sulfur at Gale Crater

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe, Part II

Presenting Author:

Lucy Thompson

Authors:

Thompson, Lucy Margaret¹, Gellert, Ralf², Spray, John G.³, Berger, Jeff⁴, Boyd, Nick⁵, Christian, John⁶, McCraig, Michael⁷, O'Connell-Cooper, Catherine⁸, VanBommel, Scott⁹, Yen, Albert¹⁰, Vasavada, Ashwin¹¹, Fraeman, Abigail¹²

(1) Planetary and Space Science Centre, University of New Brunswick, Fredericton, NB, Canada, (2) Department of Physics, University of Guelph, Guelph, Ontario, Canada, (3) Planetary and Space Science Centre, University of New Brunswick, Fredericton, NB, Canada, (4) Johnson Space Centre, Houston, TX, USA, (5) Physics Department, University of Guelph, Guelph, Ontario, Canada, (6) Washington University, St Louis, Missouri, USA, (7) Physics Department, University of Guelph, Guelph, Ontario, Canada, (8) University of New Brunswick, Fredericton, New Brunswick, Canada, (9) Washington University, St Louis, Missouri, USA, (10) Retired, Hermosa Beach, California, USA, (11) Jet Propulsion Laboratory, Pasadena, CA, USA, (12) Jet Propulsion Laboratory, Pasadena, California, USA,

Abstract:

Sulfur is a major element on the martian surface, having been detected both from landed and orbital missions. Understanding the associated mineralogy and its distribution has implications for past climate and aqueous conditions. Gale crater was selected as the Mars Science Laboratory (MSL) landing site owing to orbital signatures within its 5 km high central mound (Aeolis Mons, informally Mount Sharp), which are consistent with a transition from clay- to hydrated Mg-sulfate-dominated mineralogies. This transition was hypothesized to indicate a drying out event, possibly related to a global change in Mars environment at this time. 

The Canadian-built and funded Alpha Particle X-ray Spectrometer (APXS) on the Curiosity rover uses a combination of Particle-Induced X-ray Emission and X-ray Fluorescence to determine the chemistry of rocks, powdered drill fines, unconsolidated materials, and argon in the atmosphere. Elemental abundances for Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Zn and Br are quantified and reported as weight% oxides except for Cl (element%) and Ni, Zn, and Br (parts per million). Detection limits for all elements are <0.5 wt%. Thus, APXS can accurately measure and track sulfur abundances along Curiosity’s traverse. Correlations with other elements (e.g., Ca and Mg) and intensities of elastically and inelastically scattered X-rays indicative of light element concentrations (e.g., oxygen), can be used to infer mineralogy of the S-bearing phases. We report the key findings of APXS sulfur analyses along the >35 km traverse and >500 m of elevation. Highlights include: 1) the occurrence of abundant and widespread CaSO₄ veins; 2) low S bedrock dominating the base of the section (Bradbury grp) and Stimson formation sandstones; 3) transition from bedrock dominated by variation in the abundance of CaSO₄ phases to strata (Layered Sulfate unit – LSu) exhibiting addition of ~10wt% MgSO₄ phases, coincident with hydrated Mg-sulfate orbital signatures within the Mount Sharp grp; 4) identification of MgSO₄-rich diagenetic nodules and resistant features; and 5) the unexpected discovery of native sulfur within the late stage, Gediz Vallis debris flow/avalanche deposit. Current exploration of the boxwork terrain has revealed changes in S and Mg relative to the LSu, consistent with decreasing MgSO₄. We will place these findings in context and discuss the implications of the S-bearing phases detected by APXS.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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