Matching Items (14)
Description
Planetary surfaces are constantly evolving through a series of endogenic and exogenic processes. Multi-temporal observations enable the detection of these newly formed surface changes. Analysis techniques of these observations require precise image geolocation obtainable only with accurate optical and projection distortion corrections. In this study, the Clementine Ultraviolet-Visible camera is geometrically calibrated, and the spacecraft orientation knowledge is refined, aligning the entire dataset to the reference frame defined by the more recent Lunar Reconnaissance Orbiter mission. This direct registration approach improved the geolocation to within 0.084 pixels (i.e., sub-pixel), enabling new optical maturity and mineral composition maps aligned with the present reference frame.Next, new surface changes on Mercury are discovered with a geometrically calibrated Mercury Dual Imaging Camera suite. Over twenty surface changes varying in size from 450 to 4400 meters are identified that formed between 2011 to 2015. Exogenic impacts do not explain all the surface changes witnessed. Some changes occurred on slopes near prominent tectonic features suggesting a potential tie to seismic activity. A pair of other reflectance changes were identified around hollow formations, meaning the surface feature is still evolving. This temporal dataset provides the first direct evidence of endogenic and exogenic activities of the innermost planet.
Lastly, the color and photometric properties of newly formed impact craters are explored using hundreds of observations acquired before and post-impact. These observations reveal new details about the distal surface changes associated with the impact process. Phase ratio imaging enables a measurement of the phase curve slope, including near opposition (phase ~ 0°). While the entire proximal ejecta blanket shows an increase in the optical surface roughness properties, the region adjacent to the crater rim (1.0 to 1.25 crater radii from the center) expresses a broadening of the opposition surge consistent with the presence of fine-scale surface particles and rocks. Finally, Hapke parameters and color maps are also derived for the entire region before and after the impact event to quantify changes in surface properties and the maturity state of the regolith. This work provides new insight into the broad extent of surface modifications around newly formed craters.
ContributorsSpeyerer, Emerson (Author) / Robinson, Mark S (Thesis advisor) / Bell, James F (Committee member) / Hervig, Richard L (Committee member) / Scowen, Paul A (Committee member) / Zolotov, Mikhail Y (Committee member) / Arizona State University (Publisher)
Created2023
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
Both volcanism and impact cratering produce ejecta and associated deposits incorporating a molten rock component. While the heat sources are different (exogenous vs. endogenous), the end results are landforms with similar morphologies including ponds and flows of impact melt and lava around the central crater. Ejecta from both impact and volcanic craters can also include a high percentage of melted rock. Using Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC) images, crucial details of these landforms are finally revealed, suggesting a much more dynamic Moon than is generally appreciated. Impact melt ponds and flows at craters as small as several hundred meters in diameter provide empirical evidence of abundant melting during the impact cratering process (much more than was previously thought), and this melt is mobile on the lunar surface for a significant time before solidifying. Enhanced melt deposit occurrences in the lunar highlands (compared to the mare) suggest that porosity, target composition, and pre-existing topography influence melt production and distribution. Comparatively deep impact craters formed in young melt deposits connote a relatively rapid evolution of materials on the lunar surface. On the other end of the spectrum, volcanic eruptions have produced the vast, plains-style mare basalts. However, little was previously known about the details of small-area eruptions and proximal volcanic deposits due to a lack of resolution. High-resolution images reveal key insights into small volcanic cones (0.5-3 km in diameter) that resemble terrestrial cinder cones. The cones comprise inter-layered materials, spatter deposits, and lava flow breaches. The widespread occurrence of the cones in most nearside mare suggests that basaltic eruptions occur from multiple sources in each basin and/or that rootless eruptions are relatively common. Morphologies of small-area volcanic deposits indicate diversity in eruption behavior of lunar basaltic eruptions driven by magmatic volatiles. Finally, models of polar volatile behavior during impact-heating suggest that chemical alteration of minerals in the presence of liquid water is one possible outcome that was previously not thought possible on the Moon.
ContributorsStopar, Julie D (Author) / Robinson, Mark S. (Thesis advisor) / Bell, James (Committee member) / Christensen, Philip R. (Philip Russel) (Committee member) / Clarke, Amanda (Committee member) / Scowen, Paul (Committee member) / Arizona State University (Publisher)
Created2016
Description
The lunar poles have hydrated materials in their permanently shadowed regions (PSRs), also known as lunar cold traps. These cold traps exist because of the Moon’s slight tilt of 1.5, which consequently creates these PSRs. In these shadows, the temperature remains cold enough to prevent the sublimation of volatile materials for timescales spanning that of geologic times [Hayne et. al 2015]. PSRs are significant because they create an environment where water ice can exist within the first meter of regolith at the lunar poles, where many cold traps are present. These volatile materials can be observed through a process called neutron spectroscopy. Neutron spectroscopy is a method of observing the neutron interactions caused by galactic and extragalactic cosmic ray proton collisions. Neutron interactions are more sensitive to hydrogen than other elements found in the regolith, and thus are a good indicator of hydrated materials. Using neutron spectroscopy, it is possible to detect the hydrogen in these cold traps up to a meter deep in the regolith, thus detecting the presence of hydrated materials, water, or ice.
For this study, we used the Monte Carlo Neutral Particle Transport Code (MCNP6) to create a homogenous sphere that represented the PSRs on Moon, and then modeled five differing water contents for the lunar regolith ranging from 0-20 percent weight. These percent weights were modeled after the estimates for Shackleton crater, data from Lunar Reconnaissance Orbiter (LRO) mission, and data from Lunar Orbiter Laser Altimeter (LOLA).
This study was created with the LunaH-Map mission as motivation, seeking to exhibit what neutron data might be observed. The LunaH-Map mission is an array of mini-Neutron Spectrometers that will orbit the Moon 8-20 km away from the lunar surface and map the spatial
distribution of hydrogen at the lunar poles. The plots generated show the relationship between neutron flux and energy from the surface of the Moon as well as from 10km away. This data provides insight into the benefits of collecting orbital data versus surface data, as well as illustrating what LunaH-Map might observe within a PSR.
For this study, we used the Monte Carlo Neutral Particle Transport Code (MCNP6) to create a homogenous sphere that represented the PSRs on Moon, and then modeled five differing water contents for the lunar regolith ranging from 0-20 percent weight. These percent weights were modeled after the estimates for Shackleton crater, data from Lunar Reconnaissance Orbiter (LRO) mission, and data from Lunar Orbiter Laser Altimeter (LOLA).
This study was created with the LunaH-Map mission as motivation, seeking to exhibit what neutron data might be observed. The LunaH-Map mission is an array of mini-Neutron Spectrometers that will orbit the Moon 8-20 km away from the lunar surface and map the spatial
distribution of hydrogen at the lunar poles. The plots generated show the relationship between neutron flux and energy from the surface of the Moon as well as from 10km away. This data provides insight into the benefits of collecting orbital data versus surface data, as well as illustrating what LunaH-Map might observe within a PSR.
ContributorsEttenborough, Ivy E (Author) / Hardgrove, Craig (Thesis director) / Wadhwa, Meenakshi (Committee member) / Czarnecki, Sean (Committee member) / School of Earth and Space Exploration (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2020-05