High-Resolution Studies Of Aqueous Environments On Ancient Mars

Wray, James

High-Resolution Studies Of Aqueous Environments On Ancient Mars

Abstract

Hydrated minerals on the surface of Mars record past aqueous conditions and permit assessment of whether, where, and when the planet may have been habitable. Both phyllosilicates (e.g., clays) and hydrated sulfate minerals were recently identified via orbital near-infrared spectroscopy. This work uses the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and High Resolution Imaging Science Experiment (HiRISE) to characterize these and other aqueous mineral deposits, determining their composition, stratigraphy, and morphology. These properties and observations from other Mars-orbiting instruments allow formulation and testing of hypotheses on how Martian environments varied across space and time. The Mawrth Vallis region hosts the largest areal exposure of phyllosilicates, and CRISM spectral maps show these are compositionally stratified, with Al-clays overlying Fe/Mg-clays throughout the region. Geometric measurements reveal that the Al-clay horizon traces the Mawrth Vallis topography, implying that the Al-clays postdate this channel and may have formed via surface weathering. CRISM data further reveal the Ca-sulfate bassanite in outcrops underlying Fe/Mg-clays. Each hydrated unit exhibits ubiquitous meter-scale polygons or other fracture patterns, which correlate with composition. A CRISM-based survey of Mars' ancient southern highlands uncovers numerous aqueous deposits undetected at lower resolution. Fe/Mg-phyllosilicates are widespread, in some cases exposed by craters and elsewhere spanning the intercrater plains. Sulfates occur at higher latitudes than those observed previously, and are associated with phyllosilicates in some locations. Elsewhere, phyllosilicates co-occur with other hydrated silicates or putative chlorides. Fe/Ca-carbonate is also identified for the first time. These diverse mineral assemblages likely reflect diverse aqueous conditions. Columbus crater and others in Terra Sirenum contain layered deposits with diverse clays and sulfates. Digital elevation models, crater counts, thermal emission spectra, and hydrologic modeling results are added to CRISM and HiRISE image analyses to test several different hypotheses for these deposits, including their possible formation in a deep lake within Columbus crater during the Late Noachian Epoch. CRISM analysis of Endeavour crater in Meridiani Planum reveals Fe/Mgsmectite clays in its rim and hydrated sulfates on the adjacent plains. Opportunity is currently driving toward these locations, which may provide the first ground truth of hydrated minerals detected from Mars orbit.

Date Issued

2011-01-31

Keywords

Mars; Remote sensing; Hydrated minerals

Committee Chair

Squyres, Steven Weldon

Committee Member

Lloyd, James
Isacks, Bryan Leonard
Bell, James F
Kay, Robert Woodbury

Degree Discipline

Astronomy

Degree Name

Ph. D., Astronomy

Degree Level

Doctor of Philosophy

Types

dissertation or thesis