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DIX Planetary Science Seminar

Tuesday, June 13, 2023
4:00pm to 5:00pm
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South Mudd 365
Chemical Weathering Conditions on Mars as Indicated by Aluminum Phyllosilicates and Associated Mineralogy/From spectra to mineralogy: a remote sensing approach to arid dust source regions
Abby Keebler, Graduate Student, Planetary Sciences, California Institute of Technology,
Sam Baker, Graduate Student, Planetary Sciences, California Institute of Technology,

Samantha Baker - Aluminum-phyllosilicates have been detected in upper stratigraphic units as the infrared spectrally dominant mineral in 100s–1000s of km2 exposures of Noachian (~3.7 Ga) bedrock across Mars. These units have been previously proposed to be analogous to terrestrial basalt weathering sequences. However, they lack the typically-associated ferric oxides and instead appear associated with jarosite (KFe3(SO4)2(OH)6) and alunite (KAl3(SO4)2(OH)6), sulfate minerals indicative of strongly acidic weathering conditions. Understanding what these and other indicator phases reveal about the origin of the Al-phyllosilicates and Mars' aqueous history requires a detailed and thorough analysis of their chemistry and context. We examine visible–near-infrared hyperspectral imagery from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to determine the spatial distribution of these phyllosilicate units and to catalog accompanying minerals that are possibly representative of such chemical weathering conditions as pH and redox state. We map the distribution of these minerals in the Nili Fossae region of Mars and find that jarosite is far more spatially constrained than Al-phyllosilicate, suggesting possible localized acidity and sulfur-rich conditions. We combine CRISM data with digital elevation models from the Mars Context Camera and high-resolution imagery from the HiRISE camera to understand the stratigraphic relationships between these minerals and, through them, to reconstruct the processes and chemistry of their formation.

Abigail M. Keebler - As Earth's climate changes, our need to understand the complex processes controlling climate and Earth's biogeochemical cycles increases. Major Earth systems models consider the role of atmospheric mineral dust, which is known to have a net radiative forcing effect in the atmosphere, influence cloud formation, and alter ocean biogeochemistry, among other roles. However, the nature and extent of mineral dust aerosols' impacts on climate cycles depends on its mineralogy and grain size and is currently unclear, including whether dust has a warming or cooling effect and how it influences cloud formation. The Earth Surface Mineral Dust Source Investigation (EMIT) is collecting visible/near infrared (VNIR) spectral data of dust source region land areas to inform how emitted dust mineralogy affects the climate system. Here we develop improved methods to derive mineralogy quantitatively from VNIR spectra. We develop a dataset of representative desert dust source sediments with VNIR spectra and XRD-derived mineralogy. Here, we examine sources of spectral variability in desert dust source material and present progress in trialing existing methods for extracting mineralogical data from spectra. We develop a novel database of natural soils sampled from arid dust source regions, focusing on soils previously excluded from agricultural-leaning atlases and directly linking natural soil spectra to known mineral composition and grain size distribution. Qualitative analyses, spectral parameterization, and statistical techniques were applied to the dataset to understand mineral sources of variability in arid soils' VNIR spectra and relate these to lab-determined mineralogy. We also employ Hapke radiative transfer modeling to extract mineralogy and compare results to lab-derived mineralogy.

For more information, please contact Ryleigh Davis by email at [email protected].