No description available.

Phyllosilicates are widespread on Noachian to Early Hesperian terrains on Mars and can help constrain the planet’s geologic and environmental history, particularly its aqueous and redox history, which in turn can provide clues about past habitability. A range of ferrous and mixed-valence smectites were synthesized and then exposed to varying O2 fluxes under dry conditions to determine if Fe/Mg trioctahedral smectites can be oxidized without an aqueous medium to form dioctahedral smectites like those observed on the surface of Mars. The appearance of a secondary peak in some unaltered samples indicates a separate phase formed during synthesis, which remained throughout the oxidation process. Partial oxidation was achieved by all samples, but only those with the highest starting Fe3+ content reached almost complete oxidation. Rapid initial oxidation was observed for all samples, but seemed to subside before oxidation was complete, indicating the process becomes unfavorable after a certain point. All three O2 fluxes used in this study were successful in partially oxidizing the smectite samples but no correlation was observed between O2 flux and actual amount of oxidation, i.e., a higher O2 flux does not necessarily result in higher production of ferric iron. The process of oxidation did cause octahedral sheet contraction in some cases; however, in some samples octahedral sheet expansion was observed with oxidation. No additional phases were formed upon oxidation and no Fe ejection was observed. Overall, the amount of oxidation observed for all samples indicates that O2 alteration of trioctahedral smectites into dioctahedral smectites can proceed under dry conditions, meaning oxidation could have continued on Mars after surface water dried up. / Geology

<p>The solar system that we live in today bears only a passing resemblance to the solar system that existed 4.5 billion years ago. As our young star shed the gas nebula from which it was born, a disk of dust and rocky bodies emerged in the space between the Sun and Jupiter. Over the next hundred million years, this planetary disk evolved and gave rise to the terrestrial planets of the inner solar system. Clues left behind during this early stage of evolution can be seen in the orbital architecture of the modern planets, the cratering records of rocky bodies, and the signatures of the solar system's secular modes. </p> <p><br></p> <p>Past works in the fields of terrestrial planet accretion and solar system evolution typically do not include collisional fragmentation. While the mechanics of collisional fragmentation are well studied, the incorporation of this processes into simulations of terrestrial planet formation is computationally expensive via traditional methods. For this reason, many works elect to exclude collisional fragmentation entirely, improving computational performance but neglecting a known process that could have played a significant role in the formation of the solar system. In this dissertation, I develop a collisional fragmentation algorithm, called Fraggle, and incorporate it into the n-body symplectic integrator Swiftest SyMBA. Along with performance enhancements and modern programming practices, Swiftest SyMBA with Fraggle is a powerful tool for simulating the formation and evolution of the inner solar system. </p> <p><br></p> <p>In this dissertation, I use Swiftest SyMBA} with Fraggle to study the effect of collisional fragmentation on the accretion and orbital architecture of the terrestrial planets, as well as the cratering record of early Mars. I show that collisional fragmentation is a significant process in the early solar system that creates a spatially heterogeneous and time-dependent population of collisional debris that fluctuates as the solar system evolves. This ever-changing population results in cratering records that are unique across the inner solar system. The work presented in this dissertation highlights the need for independent cratering chronologies to be established for all rocky bodies in the solar system, as well as the need for future models of solar system accretion to include the effects of collisional fragmentation. </p> <p><br></p> <p>While the cratering records and orbits of the terrestrial planets are two means by which to study the solar system's ancient past, analysis of the evolution of the secular modes of the solar system offers a third method. A secular mode arises due to the precession of the orbit of a planet over time. Each body's orbit precesses at a specific fundamental frequency, or mode, that has the power to shape the orbital architecture of the solar system. I show that jumps in the eccentricity of Mars can trigger short-lived power sharing relationships between secular modes, resulting in periods in which the strength and fundamental frequencies of modes fluctuates. While evidence of these past jumps in Mars' eccentricity would likely not be visible today in the secular modes of the inner solar system, the work presented in this dissertation poses additional questions. In particular, questions related to other possible triggers of power sharing relationships, as well as the effects of power sharing relationships on the stability of small bodies during these periods of fluctuation, are particularly compelling.</p> <p><br></p> <p>The work presented in this dissertation contributes to the fields of numerical modeling, solar system evolution, collisional fragmentation, martian cratering, and secular modes and resonances. As a whole, it explores avenues by which we can understand the very earliest period of our solar system's history and develops a model that will allow for continued research in this field. </p>

<p dir="ltr">This work focuses on understanding the response of sulfides and Fe-oxides to space weathering through the analysis of returned samples and laboratory simulations </p>

Exploring the Planets (http://explanet.info) is a free online college textbook covering thebasic concepts of planetary science emphasizing the character and evolution of the planetarybodies in the Solar System. The latest edition (3rd edition) was published online in 2007 by EricH Christiansen. Since the release of the third edition, two important planetary missions havebeen completed: MESSENGER (to Mercury) and New Horizons (to Pluto). These missionsprovided new information and fundamental insights into these planetary bodies, which have notyet been included in Exploring the Planets. The modern results based on recent investigations ofMercury and Pluto are critical for our understanding of the nature and history of these bodies andthe Solar System and build upon the previous information on Mercury and Pluto gained fromMariner 10 (1974-1975) and the Hubble Space Telescope, respectively. These two planetarybodies are end members in a spectrum of objects in the Solar System. Mercury is small, hot,dense, and a silicate metal rich end member of the planets, helping scientists understand thethermal and accretionary evolution of the terrestrial planets. Pluto is cold, icy, distant from theSun, and a representative object of the vast Kuiper Belt, and is thus another end member amongplanetary bodies. These two bodies refine models of how different planets will evolve over time,and how our Solar System has evolved. For these reasons, it is important to update Exploring thePlanets to summarize the current understanding of the geology of Mercury and Pluto. This way,students can better understand their formation and evolution and the implications for theevolution of our Solar System.

No description available.

<p>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.</p> <p>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.</p> <p>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. </p>

<p dir="ltr">Here we present two studies of different aspects of meteoritic impacts. The first study is about the behavior of ejecta plumes after a hypervelocity impact onto a body with an atmosphere. The second study looks at the effect vaporization has on meteoroids as they descend through Earth's atmosphere, specifically the effect permeability and meteor size have on the vaporization during their explosive fragmentation.</p><p dir="ltr">Atmospheres play an important role in ejecta deposition after an impact event. Many impact experiments and simulations neglect the effect of atmospheres. In the first study, we simulate ejecta plumes created by craters with transient diameters of 2 km and 20 km on Mars and Earth to show the difference atmospheric density and crater size have on the strength of the interaction. The interaction of ejecta with an atmosphere is explored in this study using a two-fluid hydrocode that simultaneously simulates ejecta and atmospheres as coupled, continuum fields to correctly capture the transfer of mass, energy, and momentum between the two. Here we study the effect of vaporization of plume material as well as the effect of the bow shock. We find that only the fastest ejecta is vaporized with a peak vaporized mass of 2.5x10⁵ kg, 3.5 s after the impact in our 2 km diameter Terrestrial crater. Terrestrial meteorites are preferentially formed from the fastest ejecta. However, that fastest ejecta is mostly vaporized in our simulations, so to form a Terrestrial meteorite there must be a sufficiently large impact for solid material to be ejected and not vaporize. Thus, we place a lower limit of 33 km on the size of crater needed to generate terrestrial meteorites, but the crater size needed could be substantially larger. The bow shocks in our simulations result in lofting of ejecta, especially vaporized material, in the wake of the impactor. We find that Mars' thin atmosphere slows the ejecta but does not significantly change the trajectory of the plume. Earth's atmosphere can stop and entrain ejecta particles to suspend heated material long after the majority of material has already been deposited, resulting in 4x10¹⁰ kg of material being suspended in the atmosphere 100 seconds after the impact for a 2 km diameter crater. For larger craters, we find that Earth's atmosphere has a more limited effect and ejecta more closely follows a ballistic trajectory.</p><p dir="ltr">The 1908 Tunguska bolide event and the 2013 Chelyabinsk bolide event underscore the potential damage posed by relatively small meteoroids as compared to the dinosaur-killing Chicxulub meteoroid. In this study, we model Tunguska- and Chelyabinsk-sized bolide events, extending the work of Tabetah and Melosh (2018) by exploring a larger parameter space and introducing the novel feature of material vaporization. Building upon their findings that the porosity and permeability of a meteoroid significantly influence fragmentation, we investigate additional factors such as meteoroid size, entry speed, and entry angle. Furthermore, we demonstrate that vaporization plays a crucial role, lowering the fragmentation height by extracting energy through latent heat. We find that a larger meteoroid size or higher entry speed increases the amount of vaporization that occurs while lowering the altitude of disruption of the meteoroid, and that a shallower entry angle decreases the amount of vaporization and increases the altitude of disruption. Our study not only refines the understanding of bolide events but also introduces a novel perspective with potential implications for planetary science and impact risk assessment.</p>

<p>The present-day sedimentary rock record on Mars provides insights into the early surface and subsurface geologic processes. Understanding the sediment characteristics in different environments can help to constrain the climate regimes, potential for habitability, and provide a record of ancient surface processes. The research presented in this dissertation uses complementary remote sensing techniques and datasets from rovers at the surface, satellites in orbit, and at terrestrial analogs that are relevant to current Mars exploration to better characterize alteration through water-rock alteration at multiple scales.</p><p>The martian field site for this work is Mt. Sharp, a 5-kilometer-high mountain in Gale crater that is predominantly composed of fluviolacustrine strata overlain by aeolian strata. At the rover-scale, the effects of large clay-mineral rich deposits were characterized using landscape- and hand lens-scale visible images from the Mastcam and MAHLI instruments, and multispectral visible/near-infrared images from Mastcam (445-1013 nm). Detailed analysis of the observed textures and spectral properties showed that the clay-rich deposits preserve the early surface environment, based on their lack of diagenetic features. While the regions immediately surrounding the clay-rich deposit experienced prolonged exposure to water, leading to enhanced alteration zones, and destroying characteristics from the early environment but providing insight into later water-rock processes.</p><p>At the orbital-scale, three visually distinct, dark-toned, and erosion-resistant layers were mapped and characterized using visible to short wave infrared hyperspectral (700-2650 nm) and image data. Two of these units have been identified as either aeolian or lacustrine through in situ rover investigations and the third unit will not be explored in situ so its origin can only be constrained through orbital analyses. We conducted a comparison of the morphological and spectral properties of the two known units to constrain whether their respective environments can be differentiated from orbit and apply this knowledge to the unknown third unit. The composition of all three units is similar, dominated by mafic minerals, suggesting a similar sediment source. The morphology is distinct between the lacustrine and aeolian units, with the unknown unit having similar morphology as the lacustrine unit, suggesting similar environments. We propose that the lacustrine unit in this study likely represent short-timescale transitions between wet and dry environments, where mafic sands are exposed to water prior to burial and lithification. While in the aeolian unit, most water-rock interactions occur upon lithification and later diagenesis. This has climatic implications in terms of the presence of surface water as these units were deposited as part of the original Mt. Sharp strata (i.e., the lacustrine unit) while some mantling existing topography (i.e., the aeolian and unknown units), representing similar processes but at a much later time.</p><p>The terrestrial analog field site for this dissertation was conducted in Iceland which represents a cold and wet/icy climate. We characterized sediments produced through glaciovolcanism and how they are sorted and altered through transport from source to sink along to characterize unique identifiers of glaciovolcanism that can be determined with Mars-relevant techniques. Decorrelation stretched visible images and lab visible/near-infrared reflectance and thermal-infrared emission data sets (400-2500 nm and 1200-400 cm-1, respectively) show that it is possible to differentiate sediments from glaciovolcanic and subaerial volcanic systems. In some glaciovolcanic systems, a high glass abundance (50-90 %) is observed in sediment grains due to the erosion of hyaloclastite and hyalotuff, deposits that form in water- and ice-magma interactions. These glass grains did not readily breakdown physically or chemically during transport, suggesting that they could still be observed on the martian surface today and be used to identify possible glaciovolcanic deposits.</p><p>The research described in this thesis improves the understanding of different geologic environments using remote sensing techniques and their climatic implications. This will help to better constrain early environments on Mars and identify areas where water may have been present through the rock record, as observed from the surface and from orbit.</p>

Recent geodynamic modeling studies suggest that the geometry of structural landforms in the Ouachita Mountains (OM) has been influenced by the reactivation of a weak scar in the mantle-lithosphere during intracontinental orogenesis. As deformation on one-plate planets such as Mars can be considered intracontinental, and impact cratering deeply scarred the Martian lithosphere, we hypothesize that structural geometries on Mars may also reflect heterogenous networks of lithospheric scarring. To investigate this hypothesis, we model the pre-erosional fold structure of the Maumelle Chaotic Zone in the OM to compare fault and fold geometries with that of the seismically-imaged mantle-lithosphere scar. We then numerically model deformation within the Martian crust and mantle-lithosphere in the presence of scarring to understand tectonic reactivation on one-plate planets. We find that structural geometries in the OM are consistent with a subsurface scar, and tectonic landforms on the surface of Mars may indeed reflect deformation generated by a network of lithospheric heterogeneity.