Theses and Dissertations from UMD
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Item Investigating the Internal Structure of Earth and Mars with Seismic Body Waves(2020) Huang, Quancheng; Schmerr, Nicholas C.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Seismic waves propagating through the interior of planetary bodies arepowerful imaging tools for revealing a high-resolution picture of their internal structures. Owing to the abundant seismic data on Earth, seismology has provided robust constraints on Earth’s 1-D and 3-D internal structures. Deployments of seismometers on other terrestrial planets via spacecraft missions has opened the door to explore the interior of these planets through planetary seismology. My dissertation seeks to understand the mantle structures and dynamics of Earth and Mars using a joint approach of seismic data analysis and synthetic waveform modeling. I utilized a body wave approach, SS precursors, to investigate the topography and seismic anisotropy structures of Earth’s mantle transition zone (MTZ). On Mars, I investigated the signatures of a seismic discontinuity associated with the olivine-to-wadsleyite phase transition in martian mantle using seismic data recorded by NASA’s InSight Mission. Global topography of MTZ discontinuities is characterized by regional thinning beneath hot spots and thickening beneath subduction zones, indicating mantle temperature plays a crucial role in the topography of MTZ discontinuities. I demonstrated with 3-D synthetic modeling that SS precursors can detect at least 3% azimuthal anisotropy in the MTZ as well as distinguish anisotropy from the shallow and deep upper mantle. I observed azimuthal anisotropy in the MTZ beneath subduction zones with SS precursors and the fast directions are predominantly trench-perpendicular, which is attributed to the lattice preferred orientation of wadsleyite. This is interpreted as the 3-D toroidal flow caused by trench migration. On Mars, I investigated the detectability of the MTZ, and found that that triplicated waves are the most suitable phases for sensing the olivine phase changes. I combined a polarization filter and vespagram techniques to identify body waves in InSight data. I discovered the existence of multiple reflected waves in the near-field, and evidence for triplicated waves in the far-field after aligning Marsquakes on P- and S-arrivals. Preliminary depth estimate of olivine-to-wadsleyite phase transition from the triplications indicates a cold or hydrated martian mantle. A new seismology-based picture of the martian interior is emerging from my work on the InSight data.Item DYNAMIC MELT PROCESSES IN THE LITHOSPHERES OF MARS AND IO(2020) Schools, Joseph William; Montesi, Laurent G. J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The interior structures of planetary bodies beyond the Earth are broadly unknown. Our observational capacity is largely limited to surface imagery from spacecraft. The work presented in this dissertation uses novel modeling methods of melt migration and melt focusing processes to illuminate the thermal and structural characteristics of the lithospheres of Mars and Jupiter’s moon Io. Models are constrained by, and inform observations of, surface volcanism. Coupled petrological-geodynamical models of one-dimensional melt migration are performed to determine the depth of impermeable boundaries, known as permeability barriers, in the lithosphere of Mars. Relatively deep permeability barriers are found to be prevalent throughout Martian history unless in regions of high strain rate (10^-13 s^-1), or a wet mantle (25-1000 ppm H2O). Permeability barrier depth is suggested to be linked to the style of volcanic edifice seen at the surface, with deep barriers creating larger edifices like shield volcanoes, and shallower barriers creating widespread flows. Similar petrological-geodynamical models performed for the lithosphere of Io reveal that permeability barriers always form at the base of the lithosphere due to the cold temperatures caused by geologically rapid resurfacing (~1 cm/yr) and subsidence. Melt may ascend closer to the surface in areas with a low subsidence rate (0.02 cm/yr) Two-dimensional numerical models of melt migration in the Martian lithosphere suggest that convection in a highly porous layer beneath a permeability layer (a decompaction channel) focuses melt over the convective wavelength. Melt ascends in the lithosphere at this wavelength which is reflective of volcano spacing at the surface for Hesperian aged terrains. Numerical and analytical models of melt flow through the asthenosphere and lithosphere of Io constrain the lifespan of its volcanic plumbing systems. A 1 km conduit will fully close within ~10,000 years while a 25 km conduit of melt will close within 6-7 million years. Solid convection in the asthenosphere is found to be necessary for melt focusing to heat pipe centers at the base of the lithosphere, however it is counterintuitively found that an arrangement with downwelling undeath the eruptive center is the most efficient for melt extraction.Item FUNDAMENTAL UNDERSTANDING OF HELICOPTER AEROMECHANICS ON MARS THROUGH CHAMBER TESTING AND HIGH-FIDELITY ANALYSIS(2020) Escobar, Daniel; Datta, Anubhav; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The fundamental aeromechanics of rotary-wing flight on Mars is explored. The exploration is based on chamber testing of Mars-like low Reynolds number rotors and the development of comprehensive analysis and comprehensive analysis coupled with computational fluid dynamics for systematic investigation of aeromechanical phenomena--critical for weights and packaging for Mars. The investigation includes rotor airloads, structural loads, and control loads, comparison of hingeless and articulated hubs, hover and forward flight, and the impact of fuselage aerodynamics. The coaxial configuration is the baseline platform for this work. The use of a helicopter on Mars would dramatically increase the speed, range, and coverage of exploration by providing access to caves, craters, over polar ice, along icy scarps and recurring slope lineae that are just plain inaccessible or too dangerous for rovers. Many factors go into the design of a Mars helicopter from launch/entry loads to power to controls to packaging. Aeromechanics is only one factor, but the principal factor for efficient and effective flight that impacts everything else. This work is focused on this principal factor. Current knowledge extrapolated from Earth would allow for short hops into the Mars atmosphere. Deeper understanding of Martian aeromechanics is needed to design larger more capable aircraft. Accurate predictions are needed for performance, blade loads, control loads, and blade strike behavior. True high-fidelity is needed for unlike on Earth decades of data sets do not exist on Mars. In fact there is not even a single data set. Thus clever and innovative means of verification and validation must be found. The objective of this thesis is to carry out all of these tasks. The key conclusions are: (1) the design of aircraft, hub, blades, and controls are substantially different on Mars because of its unique aeromechanics, (2) an articulated hub can in fact have lesser danger of blade strike, (2) a hingeless hub can experience lower or only marginally higher (6-7%) flap bending moments, (3) control / pitch link loads are dramatically impacted more by choice of Mars airfoils than rotor hubs, (4) lifting-line analysis does not even begin to capture the precise magnitudes of blade passage impulsive loads, and (5) fuselage aerodynamics is irrelevant in preliminary design. These, and other interesting phenomena will be the topics of this dissertation.Item Planetary Seismology using Single-Station and Small-Aperture Arrays: Implications for Mars and Ocean Worlds(2020) Marusiak, Angela Giuliano; Schmerr, Nicholas C; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Studying geophysical station deployment on Earth is essential preparation for future geophysical experiments elsewhere in the solar system. Here, I investigated how single-station seismometers and small-aperture seismic arrays in analog settings can quantify instrument capabilities, develop methodologies to detect and locate seismicity, and constrain internal structure. First, I used a single-station seismometer in Germany to study how the NASA InSight mission could constrain core depth. I showed that InSight could recover the Martian core within ±30 km if ≥ 3 events are located within an epicentral distance uncertainty of < ±1 degree. Increasing the number of detected events reduces core depth uncertainty, and higher signal-to-noise events will not affect core depth uncertainty or recovery rate. Next, I used environmental analogs in Earth's cryosphere to quantify how seismometer placement on a mock-lander would affect instrument performance and seismic science results for a future surface mission to an icy ocean world. If mock-lander instruments were unprotected from the wind, noise levels were 50 dB higher than those on the ground. However, once seismometers were shielded via burial, noise performances were similar to the ground-coupled seismometers, although spacecraft resonances were found at frequencies ~100 Hz. For icy ocean worlds lacking atmospheres, I showed that deck-mounted flight-candidate seismometers recorded ground motion comparably to surface-deployed instrumentation, with responses similar to terrestrial seismometers at frequencies > 0.1 Hz. Finally, I investigated seismicity detection capabilities of single-station and small-aperture seismic arrays. Small-aperture arrays were more effective at distinguishing low-frequency seismic events from noise and had fewer false positive events than a single-station. The Greenland site detected a higher percentage of teleseismic and regional tectonic events while the Gulkana Glacier, Alaska site observed more high frequency events. The high frequency seismicity was interpreted as originating from moulins, drainage events, icequakes, and rockfalls. Both sites had very high frequency events (> 100 Hz) that came from poles left in the field. These studies inform landing site selection criteria, such that there were trades between detecting local seismicity at the expense of seeing more distant events, and detecting larger teleseismic events that inform on deeper internal structure.Item Morphing Waveriders for Atmospheric Entry(2019) Maxwell, Jesse R; Oran, Elaine S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary challenge for vehicles entering planetary atmospheres is surviving the intense heating and deceleration encountered during the entry process. Entry capsules use sacrificial ablative heat shields and sustain several g deceleration. The high lift produced by the Space Shuttle geometry resulted in lower rates of heating and deceleration. This enabled a fully reusable vehicle that was protected by heat shield tiles. Hypersonic waveriders are vehicles that conform to the shape of the shock wave created by the vehicle. This produces high compression-lift and low drag, but only around a design Mach number. Atmospheric entry can reach speeds from zero to as high as Mach 40. A morphing waverider is a vehicle that deflects its flexible bottom surface as a function of Mach number in order to preserve a desired shock wave shape. It was demonstrated in this work that doing so retains high aerodynamic lift and lift-to-drag ratio across a wide range of Mach number. Numerical simulations were conducted for case-study waveriders designed for Mach 6 and 8 for flight at their design conditions as well as with variations in angle-of-attack and Mach number. A single-species air model was used between Mach 1 and 12 with the RANS k-omega SST and LES-WALE turbulence models. A seven-species air model was used for Mach 15 at 60km altitude and Mach 20 at 75km. Analytical methods were used to construct a reduced-order model (ROM) for estimating waverider aerodynamic forces, moments, and heating. The ROM matched numerical simulation results within 5-10% for morphing waveriders with variations in angle-of-attack, but discrepancies exceeded 20% for large deviations of rigid vehicles from their design Mach numbers. Atmospheric entry trajectory simulations were conducted using reduced-order models for morphing waverider aerodynamics, the Mars Science Laboratory (MSL) capsule, and the Space Shuttle. Three morphing waveriders were compared to the Space Shuttle, which resulted in reduced heating and peak deceleration. One morphing waverider was compared to the MSL capsule, which demonstrated a reduction in the peak stagnation heat flux, a reduction in the peak and average deceleration, and a reduction in the peak area-averaged heating.Item Assessing the Oxidative History of Miller Range Martian Meteorites(2016) Dottin III, James Wosley; Farquhar, James; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Miller Range (MIL) Martian meteorites are oxidized nakhlites. Early studies attribute their oxidation to reduction-oxidation reactions involving assimilated sulfate. I utilize the sulfur isotope and major element composition of the MIL pairs to assess their oxidative history. MIL sulfides display an average sulfur isotope composition that is different from Nakhla sulfate and sulfide. The sulfur isotope differences produce a mixing array between juvenile sulfur and mass-independent sulfur signatures, indicating assimilation of anomalous sulfur into the melt. I estimate an fO2 of QFM (+3.5 ± 0.4) and a sulfur content of 360 ppm ± 12 – 1300 ppm ± 50. With these results, I test the hypothesis of sulfate assimilation through models of charge balance, isotope mixing, and degassing of sulfur bearing compounds. I conclude that sulfate assimilation was significant in the oxidation of the MIL pairs but, additional oxidants were assimilated.Item Dwelling Beyond: Sustainable Design On Mars(2016) Raimond, Austin Martin; Binder, Mike; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In 1620, over the course of 66 days, 102 passengers called the Mayflower their home before arriving and settling in Plymouth, New England. In the years following the Louisiana Purchase of 1803 nearly 7 million people traversed extreme wilderness in covered wagons to found and settle the American West. This year, 2015, the first spaceport has opened in anticipation of sub orbital space flights in 2017 and manned settlement flights to mars by 2026. This thesis explores the questions: In this next phase of human exploration and settlement, what does it mean to dwell beyond earth? What are the current architectural limitations regarding structure and material sustainability? And, How can architecture elevate the traditionally sterile environments of survival shelters to that of permanent dwellings?Item A Study of the Sulfur Isotopic Composition of Martian Meteorites(2012) Franz, Heather; Farquhar, James; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of Document: A STUDY OF THE SULFUR ISOTOPIC COMPOSITION OF MARTIAN METEORITES Heather B. Franz, Ph.D., 2012 Directed By: Professor James Farquhar, Department of Geology and ESSIC Sulfur is an important tracer for geochemical processes because it possesses four stable isotopes and forms natural compounds in a range of oxidation states. This element has been shown to undergo mass-independent isotopic fractionation (S-MIF) during laboratory photochemical experiments, which may provide clues to processes that have occurred both in the solar nebula and in planetary atmospheres. The surface of Mars has been found to contain ubiquitous sulfate minerals, marking this planet as an ideal candidate for sulfur isotope study. The shergottites comprise the youngest group of martian meteorites and the most representative of mantle-derived igneous rocks. Extraction and isotopic measurement of sulfur from 30 shergottites yield the first estimate of the juvenile martian sulfur composition, which matches within uncertainties that of Cañon Diablo Troilite. Analysis of martian meteorites spanning a range of ages from the shergottites, as young as ~150 Ma, to the nakhlites, ~1.3 Ga, reveals the presence of sulfur characterized by S-MIF compositions. These findings are interpreted as evidence for cycling of sulfur between an atmospheric reservoir where photochemical processing of sulfur-bearing gases occurred and a surface reservoir in which photochemical products were ultimately deposited. Anomalous sulfur has been detected in both sulfate and sulfide minerals, implying assimilation of sulfur from the martian surface into magmas. Differences in the S-MIF compositions of the nakhlites and shergottites may preserve a record of complementary sulfur formed by a single process or may indicate the operation of multiple photochemical processes at different times or geographical locations. Identification of the photochemical mechanism responsible for producing the anomalous sulfur observed in martian meteorites is important for constraining the atmospheric composition at the time the S-MIF signals were generated. Results of laboratory experiments with pure SO2 gas suggest that self-shielding is insufficient to explain the anomalous sulfur isotopic composition. This implies that an optically thick SO2 column in the martian atmosphere may not have been required for production of the observed signalsItem Mars Weather and Predictability: Modeling and Ensemble Data Assimilation of Spacecraft Observations(2011) Greybush, Steven J.; Kalnay, Eugenia; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Combining the perspectives of spacecraft observations and the GFDL Mars General Circulation Model (MGCM) in the framework of ensemble data assimilation leads to an improved understanding of the weather and climate of Mars and its atmospheric predictability. The bred vector (BV) technique elucidates regions and seasons of instability in the MGCM, and a kinetic energy budget reveals their physical origins. Instabilities prominent in the late autumn through early spring seasons of each hemisphere along the polar temperature front result from baroclinic conversions from BV potential to BV kinetic energy, whereas barotropic conversions dominate along the westerly jets aloft. Low level tropics and the northern hemisphere summer are relatively stable. The bred vectors are linked to forecast ensemble spread in data assimilation and help explain the growth of forecast errors. Thermal Emission Spectrometer (TES) temperature profiles are assimilated into the MGCM using the Local Ensemble Transform Kalman Filter (LETKF) for a 30-sol evaluation period during the northern hemisphere autumn. Short term (0.25 sol) forecasts compared to independent observations show reduced error (3-4 K global RMSE) and bias compared to a free running model. Several enhanced techniques result in further performance gains. Spatially-varying adaptive inflation and varying the dust distribution among ensemble members improve estimates of analysis uncertainty through the ensemble spread, and empirical bias correction using time mean analysis increments help account for model biases. With bias correction, we estimate a predictability horizon of about 5 sols during which temperature, wind, and surface pressure forecasts initialized from an assimilation analysis are superior to a free running model forecast. LETKF analyses, when compared with the UK reanalysis, show a superior correspondence to independent radio science temperature profiles. Traveling waves in both hemispheres share a correspondence in phase, and temperature differences between the analyses are generally less than 5 K. Assimilation of Mars Climate Sounder (MCS) temperature profiles reveals the importance of vertical distributions of dust and water ice aerosol in reducing model bias. A strategy for assimilation of TES and MCS aerosol products is outlined for future work.Item MARS OZONE ABUNDANCES FROM INFRARED HETERODYNE SPECTRA AND THEIR APPLICATION TO THE STUDY OF THE STABILITY OF THE MARTIAN ATMOSPHERE(2005-04-21) Fast, Kelly Elizabeth; A'Hearn, Michael F; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The stability of the carbon dioxide atmosphere of Mars is thought to be maintained through catalytic chemistry involving "odd hydrogen" products of water vapor photolysis. Ozone is destroyed by odd hydrogen and therefore its abundance is an excellent tracer of those species that play a vital role in reforming carbon dioxide. Photochemical models of the atmosphere of Mars rely on observables such as ozone to test their predictions. Infrared heterodyne spectroscopy with a spectral resolution >=106 is the only technique that can directly measure ozone in the Martian atmosphere from the surface of the Earth. Observations were made using the Goddard Infrared Heterodyne Spectrometer and Heterodyne Instrument for Planetary Wind and Composition at the NASA Infrared Telescope Facility. Ozone abundances from seven data sets taken between 1988 and 2003 are presented, along with observation and analysis techniques. Measured spatial, seasonal, and orbital variability of total ozone column abundance is compared to that predicted by the first three-dimensional gas phase photochemical model of Mars. Overall agreement in the behavior of ozone across aphelion and perihelion periods supports the theory that odd hydrogen chemistry is responsible for maintaining the stability of the carbon dioxide atmosphere. Underestimation of modeled low latitude ozone around aphelion may indicate the suppression of odd hydrogen abundance through heterogeneous processes involving water ice clouds. The weak but not strict anticorrelation of the observed total column densities of ozone and water supports the role that the altitude distribution of water vapor is thought to play in regulating ozone abundance. Ozone abundances from this work are compared with those retrieved using ultraviolet techniques, showing generally good agreement. Techniques for extracting ozone altitude distribution are investigated by incorporating O2(1D) dayglow observations which indirectly probe ozone above ~20 km altitude. The abundance and altitude distribution of ozone in the Earth's atmosphere retrieved from calibration spectra are compared to nearby contemporaneous measurements using Dobson, lidar, and ozonesonde techniques. Excellent agreement with altitude distribution measured by lidar and ozonesonde is achieved when total ozone column densities from Dobson spectrophotometry are used as a constraint in the radiative transfer analysis of the spectra.