Matching Items (5)
Description
A thorough understanding of Europa's geology through the synergy of science and technology, by combining geologic mapping with autonomous onboard processing methods, enhances the science potential of future outer solar system missions. Mapping outlines the current state of knowledge of Europa's surface and near sub-surface, indicates the prevalence of distinctive geologic features, and enables a uniform perspective of formation mechanisms responsible for generating those features. I have produced a global geologic map of Europa at 1:15 million scale and appraised formation scenarios with respect to conditions necessary to produce observed morphologies and variability of those conditions over Europa's visible geologic history. Mapping identifies areas of interest relevant for autonomous study; it serves as an index for change detection and classification and aids pre-encounter targeting. Therefore, determining the detectability of geophysical activity is essential. Activity is evident by the presence of volcanic plumes or outgassing, disrupted surface morphologies, or changes in morphology, color, temperature, or composition; these characteristics reflect important constraints on the interior dynamics and evolutions of planetary bodies. By adapting machine learning and data mining techniques to signatures of plumes, morphology, and spectra, I have successfully demonstrated autonomous rule-based response and detection, identification, and classification of known events and features on outer planetary bodies using the following methods: 1. Edge-detection, which identifies the planetary horizon and highlights features extending beyond the limb; 2. Spectral matching using a superpixel endmember detection algorithm that identifies mean spectral signatures; and 3. Scale invariant feature transforms combined with supervised classification, which examines brightness gradients throughout an image, highlights extreme gradient regions, and classifies those regions based on a manually selected library of features. I have demonstrated autonomous: detection of volcanic plumes or jets at Io, Enceladus, and several comets, correlation between spectral signatures and morphological appearances of Europa's individual tectonic features, detection of ≤94% of known transient events on multiple planetary bodies, and classification of similar geologic features. Applying these results to conditions expected for Europa enables a prediction of the potential for detection and recommendations for mission concepts to increase the science return and efficiency of future missions to observe Europa.
ContributorsBunte, Melissa K (Author) / Bell, Iii, James F. (Thesis advisor) / Williams, David A. (Committee member) / Saripalli, Srikanth (Committee member) / Clarke, Amanda B. (Committee member) / Reynolds, Stephen J. (Committee member) / Christensen, Phillip R. (Committee member) / Arizona State University (Publisher)
Created2013
Description
Finding life beyond Earth could change our understanding of life and habitability. The best place to look for life beyond Earth is Jupiter's moon, Europa. It has been estimated Europa may have a liquid, salt-water subsurface with 2 to 3 times the volume of all Earth's oceans. Knowing that all life requires water, it is in our best interest to explore Europa. This thesis explored the plausibility of life on Europa in four of its environments: on the surface, under the ice shell, in the liquid subsurface, and at the bottom of the liquid subsurface. Each of these environments were defined from science literature and compared to known Earth analogs. Europa's surface is not likely to support life, as there is not liquid water present. There is also extremely high radiation bombardment and extremely low surface temperatures that are estimated to be well out of the range for supporting life. It is more plausible that life could be under Europa's ice shell than on the surface. Under the surface, radiation exposure dramatically reduces. Researchers have found organisms on Earth that can live in similar environments as Europa's ice as well. These organisms require some interaction with liquid water though. Uncertainties about Europa's ice shell thickness and radiation load per depth it experiences, as well as there being limited research on organisms in ice environments, hinder us from definitively assessing the plausibility of life under the surface. The best environment on Europa to look for life on Europa is the subsurface. There remain a lot of uncertainties about the subsurface, however, that make it difficult to assess the plausibility of finding life. These uncertainties include its depth, water activity, salinity, temperature, pressure, and structure. This subsurface may be suitable for life, but until we can further understand the environment of the subsurface, we cannot make definite conclusions. As for assessing the plausibility of life at the bottom of Europa's subsurface, there is not much we know about this environment either. It has been suggested there may be hydrothermal vents, but no evidence has either supported or rejected this idea. Without a clear understanding of the environment at the bottom of the subsurface, the plausibility of life here cannot be definitively answered. It is apparent we need to further study Europa. In particular, we need to focus on understanding the subsurface. When the subsurface is better defined, we can better assess the plausibility of life being present. Fortunately, both NASA and the ESA are currently planning missions to Europa that are scheduled to launch in the 2020s.
ContributorsHoward, Cheyenne Whiffen (Author) / Farmer, Jack (Thesis director) / Shock, Everett (Committee member) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
The Jovian moon Europa's putative subsurface ocean offers one of the closest astrobiological targets for future exploration. It’s geologically young surface with a wide array of surface features aligned with distinct surface composition suggests past/present geophysical activity with implications for habitability. In this body of work, I propose a hypothesis for material transport from the ocean towards the surface via a convecting ice-shell. Geodynamical modeling is used to perform numerical experiments on a two-phase water-ice system to test the hypotheses. From these models, I conclude that it is possible for trace oceanic chemistry, entrapped into the newly forming ice at the ice-ocean phase interface, to reach near-surface. This new ice is advected across the ice-shell and towards the surface affirming a dynamical possibility for material transport across the ice-ocean system, of significance to astrobiological prospecting. Next, I use these self-consistent ice-ocean models to study the thickening of ice-shell over time. Europa is subject to the immense gravity field of Jupiter that generates tidal heating within the moon. Analysis of cases with uniform and localized internal tidal heating reveal that as the ice-shell grows from a warm initial ocean, there is an increase in the size of convection cells which causes a dramatic increase in the growth rate of the ice-shell. Addition of sufficient amount of heat also results in an ice-shell at an equilibrium thickness. Localization of tidal heating as a function of viscosity controls the equilibrium thickness. These models are then used to understand how compositional heterogeneity can be created in a growing ice-shell. Impurities (e.g. salts on the surface) that enter the ice-shell get trapped in the thickening ice-shell by freezing. I show the distribution pattern of heterogeneities that can form within the ice-shell at different times. This may be of potential application in identifying the longevity and mobility of brine pockets in Europa's ice-shell which are thought to be potential habitable niches.
ContributorsAllu Peddinti, Divya (Author) / McNamara, Allen Keith (Thesis advisor) / Garnero, Edward (Committee member) / Desch, Steven (Committee member) / Zolotov, Mikhail (Committee member) / Clarke, Amanda (Committee member) / Arizona State University (Publisher)
Created2017
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 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.
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
Description
Water ice is a fundamental planetary building block and ubiquitous in the outer solar system. On Ocean worlds like Europa, convecting ice may transport material from a subsurface ocean (a potential habitat) to the surface, depositing ices and salts. Evaluating the habitability of Ocean Worlds, requires either unraveling the history of ice on the surface to contextualize biosignatures, or probing the ocean for direct access. There are, however, challenges to both exploration strategies. How can recent exposures of subsurface ice be identified? How can a probe penetrate beneath an ice shell and still communicate with the surface? I have developed techniques to address these questions, and pose new ones, using a two-part approach to exploration of Ocean Worlds, viewed as both remote sensing targets, and sites for in-situ analysis. First, I combined investigations using laboratory spectroscopy and Hapke modeling to identify the diagnostic limits of existing datasets, collected optical and spectral measurements of candidate ices at relevant conditions, and identified the effects of grain size, sample thickness, and thermal cycling on water ice absorption features. I designed this dataset to enable better interpretation of Galileo and upcoming Europa Clipper mission spectra, with a focus on characterization of surface properties. To demonstrate its efficacy, I determined the bulk crystallinity of Europa’s leading hemisphere, the environmental conditions required to meet current age estimates, and developed a criterion for selection of regions of recent exposure. Second, I simulated conditions in Europa’s interior and ice shell faults using cryogenic shear experiments, to evaluate the mechanical behavior of ice and explore the limitations of communication tethers for deployment by a melt probe transiting the ice shell. Surprisingly, I find that these tethers are robust across the range of temperature and velocity conditions expected on Europa and offer capabilities as potential science instruments to detect ice-quakes and characterize the thermal profile of the ice shell. Together, these studies improve the ability to probe the thermomechanical and compositional properties of dynamic ice shells, characterize the environments likely to be encountered by landed missions, and guide future technology development for assessing the habitability of Ocean Worlds.
ContributorsSingh, Vishaal (Author) / Desch, Steven J. (Thesis advisor) / Rhoden, Alyssa R. (Thesis advisor) / Bell, James F. (Committee member) / Robinson, Mark S. (Committee member) / Gudipati, Murthy S. (Committee member) / Arizona State University (Publisher)
Created2021