Clay Minerals in Water-Lain Sedimentary Deposits in the Southern Highlands: Evaluating Habitability on Mars with MSL Ritchey Crater (Holden Crater, Eberswalde) Ralph Milliken JPL/Caltech special thanks to L. Tornabene, J. Grant, R. Irwin, J. Grotzinger, J. Rice, J. Schieber, S. Murchie, A. McEwen, and the MRO Science Teams Alluvial/Fluvial & Lacustrine Deposits in Ritchey Crater Ritchey Crater is west of the Uzboi-Ladon-Margaritifer system, but it shares many of the morphological and mineralogical traits as deposits in Eberswalde and Holden Crater. Eberswalde Holden Ritchey Nirgal Uzboi Why Ritchey Crater? - Morphologic evidence for alluvial/fluvial units (sedimentary deposits). - Possible lacustrine deposits (long-lived body of water). - Deposits are similar to those found in nearby Holden and Eberswalde fans; therefore the same processes may be recorded in these sediments, but the landing ellipse appears safer. - Clays are present within the landing ellipse! - Impacted into Noachian crust, which likely contained phyllosilicates formed earlier in Mars history. - Evidence for Fe/Mg smectites (CRISM); nearby regions as yet unmeasured by MRO may contain other phyllosilicates. - Central peak is near landing ellipse. diversity in mafic mineralogy (Noachian crust?) alteration of Noachian crust (impact glass, phyllosilicates,alteration of mafic material) can study impact processes can be used to determine stratigraphy and compare pre- and post-impact clays colorbar is backwards Wt. % H2O <2 3 >4 phyllosilicates present Representative Portion of Landing Ellipse: HiRISE Representative Portion of Landing Ellipse: CTX Presence of Clay Minerals in Landing Ellipse Ritchey Crater Landing Ellipse: Mg/Fe Clays CRISM RGB 1.06 1.04 o i t a R F / I 1.02 M S I R C 1 [Sea Red ROI 0.98 Blue ROI Green ROI Fe/Mg Smectites in Landing Ellipse Purple ROI 1.41 µm 1.91 µm 2.3 µm 1.07 0.9 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 Wavelength (um) 0.8 1.06 Saponite 0.7 0.18 CRISM Ratio Inputs 1.05 o 0.17 i t 0.6 R a e R f l 0.16 e F c / I t 1.04 Sepiolite 0.5 a n M 0.15 c I/F S I e R Nontronite 0.4 C 0.14 1.03 Numerator 0.3 0.13 (Purple ROI) Denominator Nontronite w/ Mg 1.41 µm 1.91 µm 2.3 µm 1.02 0.12 0.2 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 Wavelength (um) 2.302 µm 1.01 0.1 2 2.1 2.2 2.3 2.4 2.5 Wavelength (um) 1.08 Ritchey Crater Drive-To Location: 2.23 µm CRISM RGB Diversity in Hydrated Phases 1.06 o i t 1.04 a R F / Mg/Fe Smectite I M S I 1.02 R C Hydrated Glass (Impact?) 1 Cyan ROI Purple ROI 1.91 µm 2.31 µm 0.98 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 Wavelength (um) 1.2 Ritchey Crater Drive-To Location: Diversity in Mafics 1.15 o i t a R F / I 1.1 M S I R C 1.05 'Low' Ca-Pyroxene 'Higher' Ca-Pyroxene 1 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 Wavelength (um) colorbar is backwards Wt. % H2O <2 3 >4 Water Content in Central Peak HiRISE Color Reveals Diversity in Composition of Central Peak CRISM RGB Alluvial/Fluvial (& possible lacustrine) units exhibit spectral diversity indicative of mafic minerals and phyllsoilicates (Fe/Mg smectites). Ritchey Crater Drive-To Location: Phyllosilicates and Mafics 1.2 Clays, Mafics, Other 1.15 o i t 1.1 a R F / I M S I 1.05 R C 1 1.93 µm 2.3 µm (5181 cm -1) (4348 cm -1) 0.95 0.5 1 1.5 2 2.5 Wavelength (um) Location of Clay Minerals in Layered Deposits colorbar is backwards Wt. % H2O <2 3 >4 Northern Rim of Ritchey (CTX) Layered Deposits with Fe/Mg Smectites HiRISE color products highlight diversity in composition within layered deposits. Units with Fe/Mg smectites are light brown in these false color images. Ritchey Crater is an Excellent Site for MSL Science Goals The crater acts as a closed sedimentary basin… - thick sequence of sedimentary deposits - sequence records different depositional processes - presence of fine-grained materials (clays) - there are likely mudstones within this sequence Evidence for lots of water (amount and duration)… - fluvial features along crater wall and rim - alluvial/fluvial deposits - significant amount of sediment transported and deposited - likely that some material precipitated out of the water (interbedded sulfate, chlorides, other evaporites?) Potential to find clays formed under different environmental conditions… - clays formed in Noachian excavated by impact - clays formed by impact-induced hydrothermal alteration - clays formed in low-temperature fluvial/lacustrine setting Ritchey Crater is an Excellent Site for MSL Science Goals Diversity in mineralogy and depositional processes - clays, hdyrated glass, mafic minerals, etc. - smectites may be the key to initiation and preservation of life/organics - sediments deposited in an aqueous environment (habitability) Stratigraphy, morphology, and central peak allow for unraveling the geologic history and evaluating the potential for habitability - different facies can be used to determine the depositional environment(s) - central peak will allow us to understand impact processes and how they alter pre-existing compositions…impact-induced hydrothermal alteration? Clays are present within the landing ellipse! This will allow immediate access to materials important for addressing key science goals of MSL and evaluating the potential for habitability.