Exploring the Polar Layered Deposits of Mars through spectroscopy and rover-based analog studies
Creators: name: Sinha, Prakhar
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Planetary geology

description: Mars’ Polar layered Deposits (PLD) accumulated over the last few millions of years due to seasonal buildup of frost trapping atmospheric gasses and incoming sediments, thereby preserving the history of Mars' recent climate in the form of an ice-rich geologic record. The PLD includes both the North Polar Layered Deposits (NPLD) and the South Polar Layered Deposits (SPLD) which are estimated to be up to 5 Mya and 100 Mya old respectively. Characterizing the contents of these deposits is essential to understand the role of geologic and climatic processes recently active on Mars. The Mars scientific community recommends robotic exploration of these icy NPLD to sample the ice and extract recent climate records; however, linking the geologic record to the climatic history will require quantitative dating of the NPLD. The SPLD is thought to be older than the north polar deposits, so the stratigraphic records of the SPLD are a window to look deeper into the climatic history of Amazonian Mars. Deciphering the paleoenvironment at the PLD requires characterization of the ice-rich deposits, however, the origin, composition, transport histories, and alteration environment of sediments within the deposits are not well constrained. In this study we use orbital reflectance spectroscopy to show for the first time that dateable mafic lithics are present throughout the PLD. We find significant glass as well as diverse crystalline minerals, which suggests that surface processes like impacts and volcanism were active during the late Amazonian and transported sand-sized and finer sediments from across the planet to the poles. In situ investigation of the PLD will thus provide critical quantitative age constraint on both the recent geologic and climatic histories of Mars. Previous studies have confirmed widespread detection of sulfates at the NPLD and here we show that sulfates dominate the alteration mineralogy at the SPLD suggesting acidic, oxidizing, and evaporitic conditions. Based on this more extensive survey, previously reported rare detection of smectites and hydrated silica in the SPLD is likely due to ballistic emplacement by impacts from targets on surrounding smectite-bearing Noachian terrains. Detrital ice-rich sediments within the PLD are a complex mixture of mafic minerals and weathering products from multiple sources and are continuously reworked. In order to investigate the material and grain-size dependent effects of chemical and physical weathering in a cold and wet basaltic environment, a rover-based Mars analog study is conducted in the glacio-fluvial-aeolian landscapes of Iceland. A DCS-based color analysis technique is employed in tandem with VNIR spectroscopy and XRF analysis to develop a strategy for conducting sediment provenance. We observe that DCS-based color analysis is a powerful tool for identifying spectral diversity, and that it has the capability to differentiate primary minerals from alteration minerals. Because color analysis can aid in identifying diverse targets for sampling within the rover’s workspace, tactically, DCS colors can be used during operations to link detrital sediments within the rover’s vicinity to surrounding bedrock sources. DCS images enhance our ability to correlate observation of surface features from orbit, extend local mineralogical interpretation to surrounding regions, optimize rover’s traverse and select science targets.