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Lightning in the atmosphere of Venus is either ubiquitous, rare, or non-existent, depending on how one interprets diverse observations. Quantifying if, when, or where lightning occurs would provide novel information about Venus’s atmospheric dynamics and chemistry. Lightning is also a potential risk to future missions, which could float in the

Lightning in the atmosphere of Venus is either ubiquitous, rare, or non-existent, depending on how one interprets diverse observations. Quantifying if, when, or where lightning occurs would provide novel information about Venus’s atmospheric dynamics and chemistry. Lightning is also a potential risk to future missions, which could float in the cloud layers (~50–70 km above the surface) for up to an Earth-year. For decades, spacecraft and ground-based telescopes have searched for lightning at Venus, using many instruments including magnetometers, radios, and optical cameras. Two surveys (from the Akatsuki orbiter and the 61-inch telescope on Mt. Bigelow, Arizona) observed several optical flashes that are often attributed to lightning. We expect that lightning at Venus is bright near 777 nm (the unresolved triplet emission lines of excited atomic oxygen) due to the high abundance of oxygen as carbon dioxide. However, meteor fireballs at Venus are probably bright at the same wavelength for the same reason. Here we derive power laws that quantify the rate and brightness of optical flashes from meteor fireballs at Venus. We calculated that meteor fireballs are statistically likely to cause bright optical flashes at rates that are consistent with published observations. Small meteors burn up at altitudes of ~100 km, roughly twice as high above the surface as the clouds. Therefore, we conclude that there is no concrete evidence that lightning strikes would be a hazard to missions that pass through or dwell within the clouds of Venus.

ContributorsBlaske, Claire (Author) / O'Rourke, Joseph (Thesis director) / Desch, Steve (Committee member) / Barrett, The Honors College (Contributor) / School of Earth and Space Exploration (Contributor)
Created2023-05
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Description
Jupiter’s moon Europa is an active target of research because of its unique geology and its potential for habitability. Europa’s icy chaos disrupts and transforms the previous terrain, suggesting melting is involved. Chaos occurs alongside several types of endogenic surface features. These microfeatures are under <100 km2 in area and

Jupiter’s moon Europa is an active target of research because of its unique geology and its potential for habitability. Europa’s icy chaos disrupts and transforms the previous terrain, suggesting melting is involved. Chaos occurs alongside several types of endogenic surface features. These microfeatures are under <100 km2 in area and include uplifts and domes, pits, spots, and hybrid features. The distribution of microfeatures is known in the ~10% of the Europa’s surface that are covered by the regional mosaics (“RegMaps”). The efforts to connect microfeature formation to any kind of heat transport in Europa are confounded because microfeatures are difficult to identify outside of RegMaps because of low image resolutions. Finding microfeatures outside of RegMaps would provide new observational constraints for microfeature formation models.

First, I mapped microfeatures across four of Europa’s RegMaps and validated them against other mapping datasets. Microchaos features are the most numerous, followed by pits, domes, then hybrids. Spots are the least common features, and the smallest. Next, I mapped features in low-resolution images that covered the E15RegMap01 area to determine error rates and sources of omission or misclassification for features mapped in low-resolution images. Of all features originally mapped in the RegMap, pits and domes were the least likely to be re-mapped or positively identified (24.2% and 5%, respectively). Chaos, spots, and hybrids were accurately classified over 70% of the time. Quantitatively classifying these features using discriminant function analysis yielded comparable values of accuracy when compared to a human mapper. Finally, nearest-neighbor clustering analyses were used to show that pits are clustered in all regions, while chaos, domes, and hybrids vary in terms of their spatial clustering.

This work suggests that the most likely processes for microfeature formations is either the evolution of liquid water sills within Europa’s ice shell or cryovolcanism. Future work extending to more areas outside of the RegMaps can further refine microfeature formation models. The detection of liquid water at or near the surface is a major goal of multiple upcoming Europa missions; this work provides predictions that can be directly tested by these missions to maximize their scientific return.
ContributorsNoviello, Jessica (Author) / Rhoden, Alyssa R (Thesis advisor) / Christensen, Philip R. (Philip Russel) (Thesis advisor) / Williams, David A. (Committee member) / Robinson, Mark (Committee member) / Scowen, Paul (Committee member) / Arizona State University (Publisher)
Created2019
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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

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.
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
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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

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
Jupiter’s moon Io is tidally locked with Jupiter and falls in a 4:2:1 orbital resonance with Europa and Ganymede, driving extreme tidal heating that makes it the most volcanically active body in the solar system. Io possesses a metallic core, as does its Galilean sibling Ganymede, yet, unlike Ganymede, Io lacks

Jupiter’s moon Io is tidally locked with Jupiter and falls in a 4:2:1 orbital resonance with Europa and Ganymede, driving extreme tidal heating that makes it the most volcanically active body in the solar system. Io possesses a metallic core, as does its Galilean sibling Ganymede, yet, unlike Ganymede, Io lacks a magnetic field. Here, I investigated the potential size, composition, and cooling rate of Io’s core to help determine why Io lacks a strong dynamo. First, I used mineral physics equations to determine that the radius of the core should be between ~650 km to 950 km for a composition ranging from pure Fe to a eutectic Fe-FeS alloy. Cosmochemical constraints from meteoritic analogues yield complementary constraints on the abundance of sulfur in the metallic core (~2.67–28.6 wt%). The mantle could be either fully or partially molten. I found that the scenario of a global magma ocean creates temperatures at the base of the mantle that are possibly too hot for core convection, but that a magma sponge regime could create core-mantle boundary temperatures cooler than the melting point of pure Fe, which could promote core convection. Therefore, I conclude that Io lacks a strong dynamo likely because it has a magma ocean with temperatures too high for convection. However, the possibility that Io’s mantle is a magma sponge suggests the importance for future missions to investigate the state of Io’s magnetic field.
ContributorsLunetto, Sarah (Author) / O'Rourke, Joseph (Thesis director) / Walker, Sara (Committee member) / Barrett, The Honors College (Contributor) / School of Earth and Space Exploration (Contributor)
Created2024-05