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Description
Remote sensing in visible to near-infrared wavelengths is an important tool for identifying and understanding compositional differences on planetary surfaces. Electronic transitions produce broad absorption bands that are often due to the presence of iron cations in crystalline mineral structures or amorphous phases. Mars’ iron-rich and variably oxidized surface provides an ideal environment for detecting spectral variations that can be related to differences in surface dust cover or the composition of the underlying bedrock. Several imaging cameras sent to Mars include the capability to selectively filter incoming light to discriminate between surface materials.
At the coarse spatial resolution provided by the wide-angle Mars Color Imager (MARCI) camera aboard the Mars Reconnaissance Orbiter (MRO), regional scale differences in reflectance at all wavelengths are dominated by the presence or absence of Fe3+-rich dust. The dust cover in many regions is highly variable, often with strong seasonal dependence although major storm events can redistribute dust in ways that significantly alter the albedo of large-scale regions outside of the normal annual cycle. Surface dust reservoirs represent an important part of the martian climate system and may play a critical role in the growth of regional dust storms to planet-wide scales. Detailed investigation of seasonal and secular changes permitted by repeated MARCI imaging coverage have allowed the surface dust coverage of the planet at large to be described and have revealed multiannual replenishing of regions historically associated with the growth of storms.
From the ground, rover-based multispectral imaging acquired by the Mastcam cameras allows compositional discrimination between bedrock units and float material encountered along the Curiosity rover’s traverse across crater floor and lower Mt. Sharp units. Mastcam spectra indicate differences in primary mineralogy, the presence of iron-bearing alteration phases, and variations in iron oxidation state, which occur at specific locations along the rover’s traverse. These changes represent differences in the primary depositional environment and the action of later alteration by fluids circulating through fractures in the bedrock. Loose float rocks sample materials brought into the crater by fluvial or other processes. Mastcam observations provide important constraints on the geologic history of the Gale Crater site.
At the coarse spatial resolution provided by the wide-angle Mars Color Imager (MARCI) camera aboard the Mars Reconnaissance Orbiter (MRO), regional scale differences in reflectance at all wavelengths are dominated by the presence or absence of Fe3+-rich dust. The dust cover in many regions is highly variable, often with strong seasonal dependence although major storm events can redistribute dust in ways that significantly alter the albedo of large-scale regions outside of the normal annual cycle. Surface dust reservoirs represent an important part of the martian climate system and may play a critical role in the growth of regional dust storms to planet-wide scales. Detailed investigation of seasonal and secular changes permitted by repeated MARCI imaging coverage have allowed the surface dust coverage of the planet at large to be described and have revealed multiannual replenishing of regions historically associated with the growth of storms.
From the ground, rover-based multispectral imaging acquired by the Mastcam cameras allows compositional discrimination between bedrock units and float material encountered along the Curiosity rover’s traverse across crater floor and lower Mt. Sharp units. Mastcam spectra indicate differences in primary mineralogy, the presence of iron-bearing alteration phases, and variations in iron oxidation state, which occur at specific locations along the rover’s traverse. These changes represent differences in the primary depositional environment and the action of later alteration by fluids circulating through fractures in the bedrock. Loose float rocks sample materials brought into the crater by fluvial or other processes. Mastcam observations provide important constraints on the geologic history of the Gale Crater site.
ContributorsWellington, Danika (Author) / Bell Iii, James F (Thesis advisor) / Christensen, Philip R. (Committee member) / Robinson, Mark S (Committee member) / Sharp, Thomas G (Committee member) / Till, Christy B. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Previous workers hypothesized that lunar Localized Pyroclastic Deposits (LPDs) represent products of vulcanian-style eruptions, since some have low proportions of juvenile material. The objective of the first study is to determine how juvenile composition, calculated using deposit and vent volumes, varies among LPDs. I used Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC) digital terrain models (DTMs) to generate models of pre-eruption surfaces for 23 LPDs and subtracted them from the NAC DTMs to calculate deposit and vent volumes. Results show that LPDs have a wide range of juvenile compositions and thinning profiles, and that there is a positive relationship between juvenile material proportion and deposit size. These findings indicate there is greater diversity among LPDs than previously understood, and that a simple vulcanian eruption model may only apply to the smallest deposits.
There is consensus that martian outflow channels were formed by catastrophic flooding events, yet many of these channels exhibit lava flow features issuing from the same source as the eroded channels, leading some authors to suggest that lava may have served as their sole agent of erosion. This debate is addressed in two studies that use Context Camera images for photogeologic analysis, geomorphic mapping, and cratering statistics: (1) A study of Mangala Valles showing that it underwent at least two episodes of fluvial activity and at least three episodes of volcanic activity during the Late Amazonian, consistent with alternating episodes of flooding and volcanism. (2) A study of Maja Valles finds that it is thinly draped in lava flows sourced from Lunae Planum to the west, rendering it analogous to the lava-coated Elysium outflow systems. However, the source of eroded channels in Maja Valles is not the source of the its lava flows, which instead issue from south Lunae Planum. The failure of these lava flows to generate any major channels along their path suggests that the channels of Maja Valles are not lava-eroded.
Finally, I describe a method of locating sharp edges in out-of-focus images for application to automated trajectory control systems that use images from fixed-focus cameras to determine proximity to a target.
There is consensus that martian outflow channels were formed by catastrophic flooding events, yet many of these channels exhibit lava flow features issuing from the same source as the eroded channels, leading some authors to suggest that lava may have served as their sole agent of erosion. This debate is addressed in two studies that use Context Camera images for photogeologic analysis, geomorphic mapping, and cratering statistics: (1) A study of Mangala Valles showing that it underwent at least two episodes of fluvial activity and at least three episodes of volcanic activity during the Late Amazonian, consistent with alternating episodes of flooding and volcanism. (2) A study of Maja Valles finds that it is thinly draped in lava flows sourced from Lunae Planum to the west, rendering it analogous to the lava-coated Elysium outflow systems. However, the source of eroded channels in Maja Valles is not the source of the its lava flows, which instead issue from south Lunae Planum. The failure of these lava flows to generate any major channels along their path suggests that the channels of Maja Valles are not lava-eroded.
Finally, I describe a method of locating sharp edges in out-of-focus images for application to automated trajectory control systems that use images from fixed-focus cameras to determine proximity to a target.
ContributorsKeske, Amber (Author) / Christensen, Philip R. (Thesis advisor) / Robinson, Mark S (Committee member) / Clarke, Amanda B (Committee member) / Whipple, Kelin X (Committee member) / Bell, James F. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Understanding the history of water on Mars is one of the highest priority goals of the international Mars exploration community. Water would have played a key role in any potential abiogenesis in the past and will play a key role in the future human exploration of the planet. Chloride salts are an indicator of past hydrologic activity in the Martian geologic record and have the potential to preserve fluid inclusions and organic material within their crystal structure over geologic timescales. This dissertation will describe an innovative method for identifying chloride salts on the Martian surface, explore the implication of their distribution within Early Noachian terrains, and document important opportunistic discoveries made in the process. Decorrelation stretched Thermal Emission Imaging System (THEMIS) infrared images have long been used to identify chloride salts on Mars, but the process has been time-consuming, subjective, and qualitative. By analyzing the entire THEMIS dataset, acquired over more than twenty years at Mars, a globally-applicable covariance matrix was calculated that describes the geologic diversity of the Martian surface. This covariance matrix allows all THEMIS daytime infrared images to be translated into globally-consistent decorrelation stretch and principal component images, enabling an automatic, objective, and quantitative method for identifying chloride salts. A new global survey located 1,605 chloride salt deposits across the Martian surface, a significant increase over previous surveys. In particular, the 257 deposits in Early Noachian terrains have characteristics that indicate they formed contemporaneously with the surrounding terrain. In addition, a chloride salt formation was identified on the floor of Ares Vallis with a unique three-dimensional structure that has been interpreted as an exposed chloride salt diapir, which would indicate the presence of a significant subsurface chloride salt layer. By improving our understanding of the distribution and diversity of chloride salts on the Martian surface, this work has provided future investigators with new tools and avenues of research to explore the history of water on Mars.
ContributorsHill, Jonathon Ryan (Author) / Christensen, Philip R. (Thesis advisor) / Sharp, Thomas G (Committee member) / Ruff, Steven W (Committee member) / Simon, Molly N (Committee member) / O'Rourke, Joseph G (Committee member) / Arizona State University (Publisher)
Created2022
Description
Impact craters are ubiquitous throughout the Solar System, formed by one of the principal processes responsible for surface modification of terrestrial planets and solid bodies (i.e., asteroids, icy moons). The impact cratering process is well studied, particularly on the Moon and Mercury, where the results remain uncomplicated by atmospheric effects, plate tectonics, or interactions with water and ices. Crater measurements, used to determine relative and absolute ages for geologic units by relating the cumulative crater frequency per unit area to radiometrically-determined ages from returned samples, are sensitive to the solar incidence angle of images used for counts. Earlier work is quantitatively improved by investigating this important effect and showing that absolute model ages are most accurately determined using images with incidence angles between 65° and 80°, and equilibrium crater diameter estimates are most accurate at ~80° incidence angle. A statistical method is developed using crater size-frequencies to distinguish lunar mare age units in the absence of spectral differences. Applied to the Moon, the resulting areal crater densities confidently identify expansive units with >300–500 my age differences, distinguish non-obvious secondaries, and determine that an area >1×104 km2 provides statistically robust crater measurements. This areal crater density method is also applied to the spectrally-homogeneous volcanic northern smooth plains (NSP) on Mercury. Although crater counts and observations of embayed craters indicate that the NSP experienced at least two resurfacing episodes, no observable age units are observed using areal crater density measurements, so smooth plains emplacement occurred over a relatively short timescale (<500 my). For the first time, the distribution of impact melt on Mercury and the Moon are compared at high resolution. Mercurian craters with diameters ≥30 km have a greater areal extent of interior melt deposits than similarly sized lunar craters, a result consistent with melt-generation model predictions. The effects of shaking on compositional sorting within a granular regolith are experimentally tested, demonstrating the possibility of mechanical segregation of particles in the lunar regolith. These results provide at least one explanation toward understanding the inconsistencies between lunar remote sensing datasets and are important for future spacecraft sample return missions.
ContributorsOstrach, Lillian Rose (Author) / Robinson, Mark S (Thesis advisor) / Bell Iii, James F (Committee member) / Christensen, Philip R. (Committee member) / Clarke, Amanda B (Committee member) / Garnero, Edward J (Committee member) / Arizona State University (Publisher)
Created2013
Description
Chemical and physical interactions of flowing ice and rock have inexorably shaped planetary surfaces. Weathering in glacial environments is a significant link in biogeochemical cycles – carbon and strontium – on Earth, and may have once played an important role in altering Mars’ surface. Despite growing recognition of the importance of low-temperature chemical weathering, these processes are still not well understood. Debris-coated glaciers are also present on Mars, emphasizing the need to study ice-related processes in the evolution of planetary surfaces. During Earth’s history, subglacial environments are thought to have sheltered communities of microorganisms from extreme climate variations. On Amazonian Mars, glaciers such as lobate debris aprons (LDA) could have hosted chemolithotrophic communities, making Mars’ present glaciers candidates for life preservation. This study characterizes glacial processes on both Earth and Mars.
Chemical weathering at Robertson Glacier, a small alpine glacier in the Canadian Rocky Mountains, is examined with a multidisciplinary approach. The relative proportions of differing dissolution reactions at various stages in the glacial system are empirically determined using aqueous geochemistry. Synthesis of laboratory and orbital thermal infrared spectroscopy allows identification of dissolution rinds on hand samples and characterization of carbonate dissolution signals at orbital scales, while chemical and morphological evidence for thin, discontinuous weathering rinds at microscales are evident from electron microscopy. Subglacial dissolution rates are found to outpace those of the proglacial till plain; biologically-mediated pyrite oxidation drives the bulk of this acidic weathering.
Second, the area-elevation relationship, or hypsometry, of LDA in the midlatitudes of Mars is characterized. These glaciers are believed to have formed ~500 Ma during a climate excursion. Hypsometric measurements of these debris-covered glaciers enable insight into past flow regimes and drive predictions about past climate scenarios. The LDA in this study fall into three major groups, strongly dependent on basal elevation, implying regional and climatic controls on ice formation and flow.
I show that biologically-mediated mineral reactions drive high subglacial dissolution rates, such that variations within the valley can be detected with remote sensing techniques. In future work, these insights can be applied to examining Mars’ glacial regions for signs of chemical alteration and biosignatures.
Chemical weathering at Robertson Glacier, a small alpine glacier in the Canadian Rocky Mountains, is examined with a multidisciplinary approach. The relative proportions of differing dissolution reactions at various stages in the glacial system are empirically determined using aqueous geochemistry. Synthesis of laboratory and orbital thermal infrared spectroscopy allows identification of dissolution rinds on hand samples and characterization of carbonate dissolution signals at orbital scales, while chemical and morphological evidence for thin, discontinuous weathering rinds at microscales are evident from electron microscopy. Subglacial dissolution rates are found to outpace those of the proglacial till plain; biologically-mediated pyrite oxidation drives the bulk of this acidic weathering.
Second, the area-elevation relationship, or hypsometry, of LDA in the midlatitudes of Mars is characterized. These glaciers are believed to have formed ~500 Ma during a climate excursion. Hypsometric measurements of these debris-covered glaciers enable insight into past flow regimes and drive predictions about past climate scenarios. The LDA in this study fall into three major groups, strongly dependent on basal elevation, implying regional and climatic controls on ice formation and flow.
I show that biologically-mediated mineral reactions drive high subglacial dissolution rates, such that variations within the valley can be detected with remote sensing techniques. In future work, these insights can be applied to examining Mars’ glacial regions for signs of chemical alteration and biosignatures.
ContributorsRutledge, Alicia Marie (Author) / Christensen, Philip R. (Thesis advisor) / Shock, Everett (Committee member) / Clarke, Amanda (Committee member) / Sharp, Thomas (Committee member) / Whipple, Kelin (Committee member) / Arizona State University (Publisher)
Created2015
Description
In this thesis, I investigate possible formation processes in the northern Claritas Fossae and the large Thaumasia graben on Mars. In particular, I assess three proposed formation hypotheses for the region: a mega-landslide across the Thaumasia plateau, originating in Tharsis and moving to the south-west; a rift system pulling apart Claritas Fossae and opening the large Thaumasia graben generally propagating in a north-south direction: and extension caused by uplifting from underlying dike swarms. Using digital terrain models (DTMs) from the High Resolution Stereo Camera (HRSC) aboard Mars Express and visual images from the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter (MRO), I analyzed the geomorphic and structural context of the region. Specifically, I produced geomorphologic and structural feature maps, conducted sector diagram analyses of fault propagation direction, calculated and compared extension and strain in local and regional samples, analyzed along strike throw-profiles of faults, and conducted surface age estimates through crater counting. I found that no single formation mechanism fully explains the surface features seen in Northern Claritas Fossae today. Instead I, propose the following sequence of events led to the surface characteristics we now observe. The region most likely underwent two episodes of uplift and extension due to sub-surface magmatic intrusions, then experienced an extensional event which produced the large Thaumasia graben. This was followed by the emplacement of a layer of lava burying the bottom of the Thaumasia graben and the eastern edge of the region. Additional extension followed across the eastern portion of the study area, and finally of a young lava flow was emplaced abutting and overprinting the southwestern edge.
ContributorsStuder-Ellis, Genevieve Lynn (Author) / Williams, David A. (Thesis advisor) / Christensen, Philip R. (Thesis advisor) / Arrowsmith, J. R. (Committee member) / Arizona State University (Publisher)
Created2019
Description
Lava flow emplacement in the laboratory and on the surface of Mars was investigated. In the laboratory, the effects of unsteady effusion rates at the vent on four modes of emplacement common to lava flow propagation: resurfacing, marginal breakouts, inflation, and lava tubes was addressed. A total of 222 experiments were conducted using a programmable pump to inject dyed PEG wax into a chilled bath (~ 0° C) in tanks with a roughened base at slopes of 0, 7, 16, and 29°. The experiments were divided into four conditions, which featured increasing or decreasing eruption rates for either 10 or 50 s. The primary controls on modes of emplacement were crust formation, variability in the eruption rate, and duration of the pulsatory flow rate. Resurfacing – although a relatively minor process – is inhibited by an extensive, coherent crust. Inflation requires a competent, flexible crust. Tube formation requires a crust and intermediate to low effusion rates. On Mars, laboratory analogue experiments combined with models that use flow dimensions to estimate emplacement conditions and using high resolution image data and digital terrain models (e.g. THEMIS IR, CTX, HRSC), the eruption rates, viscosities, and yield strengths of 40 lava flows in the Tharsis Volcanic Province have been quantified. These lava flows have lengths, mean widths, and mean thicknesses of 15 – 314 km, 0.5 – 29 km, and 11 – 91 m, respectively. Flow volumes range from ~1 – 430 km3. Based on laboratory experiments, the 40 observed lava flows were erupted at 0.2 – 6.5x103 m3/s, while the Graetz number and Jeffrey’s equation when applied to 34 of 40 lava flows indicates eruption rates and viscosities of 300 – ~3.5 x 104 m3/s and ~105 – 108 Pa s, respectively. Another model which accounts for mass loss to levee formation was applied to a subset of flows, n = 13, and suggests eruption rates and viscosities of ~30 – ~1.2 x 103 m3/s and 4.5 x 106 – ~3 x 107 Pa s, respectively. Emplacement times range from days to centuries indicating the necessity for long-term subsurface conduits capable of delivering enormous volumes of lava to the surface.
ContributorsPeters, Sean (Author) / Christensen, Philip R. (Thesis advisor) / Clarke, Amanda B (Committee member) / Fink, Jonathan H. (Committee member) / Whipple, Kelin X (Committee member) / Sharp, Thomas (Committee member) / Arizona State University (Publisher)
Created2020