Student: Gabrielle Ledesma, Undergraduate Student in Geology, Iowa State University
Research Mentor: Elizabeth Swanner
Modern lakes as analogs to Gale crater deposition on Mars
The Gale crater on Mars, which once contained a redox-stratified lake, is currently being investigated by NASA’s Curiosity Rover. The ChemCam instrument on Curiosity found ~3% of Gale crater rocks have manganese (Mn) abundances greater than ~3 times expected for martian basalt values (0.4 wt% MnO). On Earth, manganese enrichments can form in aquatic settings as manganese (III, IV) oxides, characteristic of well-oxygenated environments, due to Mn’s need for high potential oxidants for oxidation (>>500mV) relative to other redox-sensitive elements such as iron. Although present-day conditions on Mars may oxidize iron and sulfur, manganese cannot be oxidized under current conditions. This leads to a hypothesis that if the observed martian manganese was precipitated as an oxide, it should be accompanied by other trace elements, as Mn-oxides strongly adsorb trace metals. However, in aquatic settings manganese can also precipitate as manganese-carbonates which is seen in Earth lake environments but carbonates have yet to be seen and interpreted by the ChemCam LIBS data received from Curiosity Rover. This project has narrowed down a set of 10 samples from both past and present Earth lake environments which are analogous to the paleolake composition, once existing in Gale crater. Both Mn-oxide and Mn-carbonate minerals have been studied within these samples and have been analyzed by LIBS under Mars pressure and atmospheric composition using the ChemCam engineering model at Los Alamos National Laboratory. This project aims at 1) identifying diagnostic peaks within the LIBS spectra of Earth samples which show Mn-carbonate presence to confirm the absence of Mn-carbonate spectral peaks in the LIBS data received back from Curiosity Rover, and 2) identify any possible links between precipitated lake Mn-minerals and trace element associations to inform the formation pathway of the Mn-minerals.