Matching Items (33)
Description
Solar system orbital dynamics can offer unique challenges. Impacts of interplanetary dust particles can significantly alter the surfaces of icy satellites and minor planets. Impact heating from these particles can anneal away radiation damage to the crystalline structure of surface water ice. This effect is enhanced by gravitational focusing for giant planet satellites. In addition, impacts of interplanetary dust particles on the small satellites of the Pluto system can eject into the system significant amounts of secondary intra-satellite dust. This dust is primarily swept up by Pluto and Charon, and could explain the observed albedo features on Pluto's surface. In addition to Pluto, a large fraction of trans-neptunian objects (TNOs) are binary or multiple systems. The mutual orbits of these TNO binaries can range from very wide (periods of several years) to near-contact systems (less than a day period). No single formation mechanism can explain this distribution. However, if the systems generally formed wide, a combination of solar and body tides (commonly called Kozai Cycles-Tidal Friction, KCTF) can cause most systems to tighten sufficiently to explain the observed distributions. This KCTF process can also be used to describe the orbital evolution of a terrestrial-class exoplanet after being captured as a satellite of a habitable-zone giant exoplanet. The resulting exomoon would be both potentially habitable and potenially detectable in the full Kepler data set.
ContributorsPorter, Simon Bernard (Author) / Desch, Steven (Thesis advisor) / Zolotov, Mikhail (Committee member) / Timmes, Francis (Committee member) / Scannapieco, Evan (Committee member) / Robinson, Mark (Committee member) / Arizona State University (Publisher)
Created2013
Description
Chemical and mineralogical data from Mars shows that the surface has been chemically weathered on local to regional scales. Chemical trends and the types of chemical weathering products present on the surface and their abundances can elucidate information about past aqueous processes. Thermal-infrared (TIR) data and their respective models are essential for interpreting Martian mineralogy and geologic history. However, previous studies have shown that chemical weathering and the precipitation of fine-grained secondary silicates can adversely affect the accuracy of TIR spectral models. Furthermore, spectral libraries used to identify minerals on the Martian surface lack some important weathering products, including poorly-crystalline aluminosilicates like allophane, thus eliminating their identification in TIR spectral models. It is essential to accurately interpret TIR spectral data from chemically weathered surfaces to understand the evolution of aqueous processes on Mars. Laboratory experiments were performed to improve interpretations of TIR data from weathered surfaces. To test the accuracy of deriving chemistry of weathered rocks from TIR spectroscopy, chemistry was derived from TIR models of weathered basalts from Baynton, Australia and compared to actual weathering rind chemistry. To determine how specific secondary silicates affect the TIR spectroscopy of weathered basalts, mixtures of basaltic minerals and small amounts of secondary silicates were modeled. Poorly-crystalline aluminosilicates were synthesized and their TIR spectra were added to spectral libraries. Regional Thermal Emission Spectrometer (TES) data were modeled using libraries containing these poorly-crystalline aluminosilicates to test for their presence on the Mars. Chemistry derived from models of weathered Baynton basalts is not accurate, but broad chemical weathering trends can be interpreted from the data. TIR models of mineral mixtures show that small amounts of crystalline and amorphous silicate weathering products (2.5-5 wt.%) can be detected in TIR models and can adversely affect modeled plagioclase abundances. Poorly-crystalline aluminosilicates are identified in Northern Acidalia, Solis Planum, and Meridiani. Previous studies have suggested that acid sulfate weathering was the dominant surface alteration process for the past 3.5 billion years; however, the identification of allophane indicates that alteration at near-neutral pH occurred on regional scales and that acid sulfate weathering is not the only weathering process on Mars.
ContributorsRampe, Elizabeth Barger (Author) / Sharp, Thomas G (Thesis advisor) / Christensen, Phillip (Committee member) / Hervig, Richard (Committee member) / Shock, Everett (Committee member) / Williams, Lynda (Committee member) / Arizona State University (Publisher)
Created2011
Description
Affect is a domain of psychology that includes attitudes, emotions, interests, and values. My own affect influenced the choice of topics for my dissertation. After examining asteroid interiors and the Moon’s thermal evolution, I discuss the role of affect in online science education. I begin with asteroids, which are collections of smaller objects held together by gravity and possibly cohesion. These “rubble-pile” objects may experience the Brazil Nut Effect (BNE). When a collection of particles of similar densities, but of different sizes, is shaken, smaller particles will move parallel to the local gravity vector while larger objects will do the opposite. Thus, when asteroids are shaken by impacts, they may experience the BNE as possibly evidenced by large boulders seen on their surfaces. I found while the BNE is plausible on asteroids, it is confined to only the outer layers. The Moon, which formed with a Lunar Magma Ocean (LMO), is the next topic of this work. The LMO is due to the Moon forming rapidly after a giant impact between the proto-Earth and another planetary body. The first 80% of the LMO solidified rapidly at which point a floatation crust formed and slowed solidification of the remaining LMO. Impact bombardment during this cooling process, while an important component, has not been studied in detail. Impacts considered here are from debris generated during the formation of the Moon. I developed a thermal model that incorporates impacts and find that impacts may have either expedited or delayed LMO solidification. Finally, I return to affect to consider the differences in attitudes towards science between students enrolled in fully-online degree programs and those enrolled in traditional, in-person degree programs. I analyzed pre- and post-course survey data from the online astrobiology course Habitable Worlds. Unlike their traditional program counterparts, students enrolled in online programs started the course with better attitudes towards science and also further changed towards more positive attitudes during the course. Along with important conclusions in three research fields, this work aims to demonstrate the importance of affect in both scientific research and science education.
ContributorsDingatantrige Perera, Jude Viranga (Author) / Asphaug, Erik (Thesis advisor) / Semken, Steven (Thesis advisor) / Anbar, Ariel (Committee member) / Elkins-Tanton, Linda T. (Committee member) / Robinson, Mark (Committee member) / Arizona State University (Publisher)
Created2017
Description
A robotic exploration mission that would enter a lunar pit to characterize the environment is described. A hopping mechanism for the robot's mobility is proposed. Various methods of hopping drawn from research literature are discussed in detail. The feasibilities of mechanical, electric, fluid, and combustive methods are analyzed. Computer simulations show the mitigation of the risk of complex autonomous navigation systems. A mechanical hopping mechanism is designed to hop in Earth gravity and carry a payload half its mass. A physical experiment is completed and proves a need for further refinement of the prototype design. Future work is suggested to continue exploring hopping as a mobility method for the lunar robot.
ContributorsMcKinney, Tyler James (Author) / Thangavelautham, Jekan (Thesis director) / Robinson, Mark (Committee member) / Asphaug, Erik (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2015-05
Description
Understanding the structural evolution of planetary surfaces provides key insights to their physical properties and processes. On the Moon, large-scale tectonism was thought to have ended over a billion years ago. However, new Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) high resolution images show the Moon’s surface in unprecedented detail and show many previously unidentified tectonic landforms, forcing a re-assessment of our views of lunar tectonism. I mapped lobate scarps, wrinkle ridges, and graben across Mare Frigoris – selected as a type area due to its excellent imaging conditions, abundance of tectonic landforms, and range of inferred structural controls. The distribution, morphology, and crosscutting relationships of these newly identified populations of tectonic landforms imply a more complex and longer-lasting history of deformation that continues to today. I also performed additional numerical modeling of lobate scarp structures that indicates the upper kilometer of the lunar surface has experienced 3.5-18.6 MPa of differential stress in the recent past, likely due to global compression from radial thermal contraction.
Central pit craters on Mars are another instance of intriguing structures that probe subsurface physical properties. These kilometer-scale pits are nested in the centers of many impact craters on Mars as well as on icy satellites. They are inferred to form in the presence of a water-ice rich substrate; however, the process(es) responsible for their formation is still debated. Previous models invoke origins by either explosive excavation of potentially water-bearing crustal material, or by subsurface drainage of meltwater and/or collapse. I assessed radial trends in grain size around central pits using thermal inertias calculated from Thermal Emission Imaging System (THEMIS) thermal infrared images. Average grain size decreases with radial distance from pit rims – consistent with pit-derived ejecta but not expected for collapse models. I present a melt-contact model that might enable a delayed explosion, in which a central uplift brings ice-bearing substrate into contact with impact melt to generate steam explosions and excavate central pits during the impact modification stage.
Central pit craters on Mars are another instance of intriguing structures that probe subsurface physical properties. These kilometer-scale pits are nested in the centers of many impact craters on Mars as well as on icy satellites. They are inferred to form in the presence of a water-ice rich substrate; however, the process(es) responsible for their formation is still debated. Previous models invoke origins by either explosive excavation of potentially water-bearing crustal material, or by subsurface drainage of meltwater and/or collapse. I assessed radial trends in grain size around central pits using thermal inertias calculated from Thermal Emission Imaging System (THEMIS) thermal infrared images. Average grain size decreases with radial distance from pit rims – consistent with pit-derived ejecta but not expected for collapse models. I present a melt-contact model that might enable a delayed explosion, in which a central uplift brings ice-bearing substrate into contact with impact melt to generate steam explosions and excavate central pits during the impact modification stage.
ContributorsWilliams, Nathan Robert (Author) / Bell, James (Thesis advisor) / Robinson, Mark (Committee member) / Christenen, Philip (Committee member) / Farmer, Jack (Committee member) / Shirzaei, Manoochehr (Committee member) / Arizona State University (Publisher)
Created2016
Description
On Mars, sedimentary deposits reveal a complex history of water- and wind-related geologic processes. Central mounds – kilometer-scale stacks of sediment located within craters – occur across Mars, but the specific processes responsible for mound formation and subsequent modification are still uncertain. A survey of central mounds within large craters was conducted. Mound locations, mound offsets within their host craters, and relative mound heights were used to address various mound formation hypotheses. The results suggest that mound sediments once filled their host craters and were later eroded into the features observed today. Mounds offsets from the center of their host crater imply that wind caused the erosion of central mounds. An in depth study of a single central mound (Mt. Sharp within Gale crater) was also conducted. Thermal Emission Imaging System Visible Imaging Subsystem (THEMIS-VIS) mosaics in grayscale and false color were used to characterize the morphology and color variations in and around Gale crater. One result of this study is that dunes within Gale crater vary in false color composites from blue to purple, and that these color differences may be due to changes in dust cover, grain size, and/or composition. To further investigate dune fields on Mars, albedo variations at eight dune fields were studied based on the hypothesis that a dune’s ripple migration rate is correlated to its albedo. This study concluded that a dune’s minimum albedo does not have a simple correlation with its ripple migration rate. Instead, dust devils remove dust on slow-moving and immobile dunes, whereas saltating sand caused by strong winds removes dust on faster-moving dunes.
On the Moon, explosive volcanic deposits within Oppenheimer crater that were emplaced ballistically were investigated. Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer mid-infrared data, LRO Camera images, and Chandrayaan-1 orbiter Moon Mineralogy Mapper near-infrared spectra were used to test the hypothesis that the pyroclastic deposits in Oppenheimer crater were emplaced via Vulcanian activity by constraining their composition and mineralogy. The mineralogy and iron-content of the pyroclastic deposits vary significantly (including examples of potentially very high iron compositions), which indicates variability in eruption style. These results suggest that localized lunar pyroclastic deposits may have a more complex origin and mode of emplacement than previously thought.
On the Moon, explosive volcanic deposits within Oppenheimer crater that were emplaced ballistically were investigated. Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer mid-infrared data, LRO Camera images, and Chandrayaan-1 orbiter Moon Mineralogy Mapper near-infrared spectra were used to test the hypothesis that the pyroclastic deposits in Oppenheimer crater were emplaced via Vulcanian activity by constraining their composition and mineralogy. The mineralogy and iron-content of the pyroclastic deposits vary significantly (including examples of potentially very high iron compositions), which indicates variability in eruption style. These results suggest that localized lunar pyroclastic deposits may have a more complex origin and mode of emplacement than previously thought.
ContributorsBennett, Kristen Alicia (Author) / Bell, James F. (Thesis advisor) / Christensen, Phillip (Committee member) / Clarke, Amanda (Committee member) / Robinson, Mark (Committee member) / Whipple, Kelin (Committee member) / Arizona State University (Publisher)
Created2016
ContributorsNemko, Deborah (Performer) / Topping, David (Performer) / Gabbard, Ray (Performer) / ASU Library. Music Library (Publisher)
Created1989-10-16
ContributorsKallenberg, Jennifer A. (Performer) / Gabbard, Ray (Performer) / Nemko, Deborah (Performer) / Weber, Steven T (Performer) / Talleda, Joseph (Performer) / Women's Choir (Performer) / ASU Library. Music Library (Publisher)
Created1991-02-28
ContributorsTalleda, Joseph (Performer) / Chavez, Ronica (Performer) / Fox, Jill (Performer) / Kallenberg, Jennifer A. (Performer) / ASU Library. Music Library (Publisher)
Created1991-04-03
ContributorsKoloch, Bradley (Performer) / Robinson, Mark (Performer) / Shaffer, Richard (Performer) / Woodrow, Marie (Performer) / Samuel, Christopher (Performer) / Listerud, L. Brian (Performer) / Graduate Chorale (Performer) / Recital Chorale (Performer) / ASU Library. Music Library (Publisher)
Created1989-11-16