Rare Jarosite Detection in CRISM Imagery by Non-Parametric Bayesian Clustering

Discovery of rare phases on Mars is important as they serve as indicators of the geochemistry of the Mars surface and facilitate understanding of mineral assemblages within a geologic unit. Identification of rare minerals in high spatial and spectral resolution Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) visible/shortwave infrared (VSWIR) images has been a challenge due to the presence of both additive and multiplicative noise and other artifacts, affecting all collected images, in addition to the limited spatial extent of regions hosting these minerals. In an effort to automate this task we evaluate various clustering algorithms using the detection of rare jarosite, associated with spectrally similar minerals in CRISM imagery, as a case study. We compare nonparametric Bayesian and standard clustering algorithms and show that a recently developed doubly nonparametric Bayesian model could be effective for this task

Enhanced Stage Variability on the Lower Missouri River as Benchmarked by Lewis and Clark: Implications for Ecosystem Restoration

Because lower Missouri River management began in the early 1800s, a challenge for present-day ecosystem restoration efforts is a lack of quantitative data on pre-management river hydrology and long-term (100+ yr.) river response to changing management practice and intensity. We address this challenge and report new results from a study spanning 200 years of lower Missouri River hydrology, encompassing natural, channelization-only, and channelization with reservoir release regimes (Ehlmann & Criss, Geology, forthcoming, Nov/Dec 2006)

An in-situ record of major environmental transitions on early Mars at Northeast Syrtis Major

The Noachian-Hesperian transition on Mars was a period marked by changes in volcanic processes and styles of aqueous alteration. Understanding the timing and nature of environmental change requires the exploration of units recording both sets of processes. Herein, we report the compositional stratigraphy of distinctive Noachian to Hesperian units along the northeastern margin of the Syrtis Major volcanic flows. A layered, polyhydrated sulfate-bearing unit with jarosite ridges has been discovered beneath the Syrtis Major lava flows and above the regionally-extensive stratigraphy of Noachian plains units reported previously. Sequential clay-, carbonate-, and sulfate-bearing units formed in-situ and record a transition from alkaline pH to acidic pH waters. The sequence is chronologically bookended by the Isidis impact and Syrtis Major flows, and is one of the most temporally-constrained and well-preserved stratigraphic sections from early Mars available for landed exploration

Controls on the Global Distribution of Martian Landsliding

Recent acquisition of high-resolution satellite imagery of the Martian surface has permitted landsliding to be studied on a global scale on Mars for the first time. We apply the Scoops3D software package to compute slope stability for select regions of the Martian surface, combining calculations of slope stability with number of observed landslides, as reported in a recently published (Crosta et al., 2018a, b) inventory of Martian landslides, to understand controls on the global distribution of landsliding on Mars. We find that the distribution of landsliding does not simply follow the distribution of unstable slopes. In particular, there is an increase in landsliding in the Tharsis Rise area, and especially in Valles Marineris and Noctis Labyrinthus, that is not explained by an abundance of unstable topography alone. We analyzed for but did not find a clear local lithologic or stratigraphic control on landslide occurrence from subsurface heterogeneities. Other possibilities to explain the increased occurrence of landslides in the Tharsis Rise include (1) regionally widespread Tharsis weak unit(s), such as from interbedded ashes and lavas; (2) seismic activity related to the Tharsis Rise’s geological activity, and (3) possible groundwater near Valles Marineris into the Amazonian. Given the apparently young ages of many landslide deposits in Valles Marineris (Quantin et al., 2004), continued modern day analysis of lithologies in Valles Marineris and observations of Martian seismicity may act to strengthen or rebut the first two hypotheses

MRO/CRISM Retrieval of Surface Lambert Albedos for Multispectral Mapping of Mars With DISORT-Based Radiative Transfer Modeling: Phase 1—Using Historical Climatology for Temperatures, Aerosol Optical Depths, and Atmospheric Pressures

We discuss the DISORT-based radiative transfer pipeline ("CRISM_LambertAlb") for atmospheric and thermal correction of MRO/CRISM data acquired in multispectral mapping mode (~200 m/pixel, 72 spectral channels). Currently, in this phase-one version of the system, we use aerosol optical depths, surface temperatures, and lower atmospheric temperatures, all from climatology derived from Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data and from surface altimetry derived from MGS Mars Orbiter Laser Altimeter (MOLA). The DISORT-based model takes the dust and ice aerosol optical depths (scaled to the CRISM wavelength range), the surface pressures (computed from MOLA altimetry, MGS-TES lower atmospheric thermometry, and Viking-based pressure climatology), the surface temperatures, the reconstructed instrumental photometric angles, and the measured I/F spectrum as inputs, and then a Lambertian albedo spectrum is computed as the output. The Lambertian albedo spectrum is valuable geologically because it allows the mineralogical composition to be estimated. Here, I/F is defined as the ratio of the radiance measured by CRISM to the solar irradiance at Mars divided by π; if there was no martian atmosphere, I/F divided by the cosine of the incidence angle would be equal to the Lambert albedo for a Lambertian surface. After discussing the capabilities and limitations of the pipeline software system, we demonstrate its application on several multispectral data cubes-particularly, the outer reaches of the northern ice cap of Mars, the Tyrrhena Terra area that is northeast of the Hellas basin, and an area near the landing site for the Phoenix mission in the northern plains. For the icy spectra near the northern polar cap, aerosols need to be included in order to properly correct for the CO_2 absorption in the H_2O ice bands at wavelengths near 2.0 µm. In future phases of software development, we intend to use CRISM data directly in order to retrieve the spatiotemporal maps of aerosol optical depths, surface pressure, and surface temperature. This will allow a second level of refinement in the atmospheric and thermal correction of CRISM multispectral data

Carbon sequestration on Mars

On Earth, carbon sequestration in geologic units plays an important role in the carbon cycle, scrubbing CO_2 from the atmosphere for long-term storage. While carbonate is identified in low abundances within the dust and soils of Mars, at <1 wt% in select meteorites, and in limited outcrops, no massive carbonate rock reservoir on Mars has been identified to date. Here, we investigate the largest exposed carbonate-bearing rock unit, the Nili Fossae plains, combining spectral, thermophysical, and morphological analyses to evaluate the timing and carbon sequestration potential of rocks on Mars. We find that the olivine-enriched (∼20%–25%) basalts have been altered, by low-temperature in situ carbonation processes, to at most ∼20% Fe-Mg carbonate, thus limiting carbon sequestration in the Nili Fossae region to ∼0.25–12 mbar of CO_2 during the late Noachian–early Hesperian, before or concurrent with valley network formation. While this is large compared to modern-day CO_2 reservoirs, the lack of additional, comparably sized post–late Noachian carbonate-bearing deposits on Mars indicates ineffective carbon sequestration in rock units over the past ∼3.7 b.y. This implies a thin atmosphere (≲500 mbar) during valley network formation, extensive post-Noachian atmospheric loss to space, or diffuse, deep sequestration by a yet-to-be understood process. In stark contrast to Earth’s biologically mediated crust:atmosphere carbon reservoir ratio of ∼10^4–10^5, Mars’ ratio is a mere ∼10–10^3, even if buried pre-Noachian crust holds multiple bars