Impact ejecta material is produced during every significant impact event in our Solar System. Bodies that possess an atmosphere and sub‐surface volatiles produce unique morphologies of ejecta that are not observed on bodies that are devoid of these properties. Recent advancements in planetary exploration have lead to an explosion in research of cratering processes on Mars and other planets. However, the enthusiasm to interpret distant worlds has led many to neglect the areas of impact processes that are still to be fully understood on Earth. In doing so, interpretations of impact ejecta processes on other planets have been based on untested models. I present here extensive research that has set out to test the validity of published models of impact ejecta processes (both distal and proximal) by critically comparing them to actual geological observations. To achieve this I have developed new techniques, conducted various detailed laboratory and field investigations, and report for the first time the discovery of 2 new layered ejecta deposits. The results of this study have shown that published models for the genesis of proximal layered ejecta deposits are flawed. I suggest an alternative model based on geological observations showing that the morphologies of proximal layered ejecta deposits are controlled by identical processes (although on a larger scale) that occur in the volcaniclastic environment. I also state that both sub‐surface volatiles (in the form of water) and atmospheric interaction play vital roles in their development. Through the analysis of the Manicouagan impact crater and its associated distal ejecta deposit I have been able to prove, for the first time, the spatial origins of distal impact ejecta showing that it is derived from the top 1/3 of the target sequence. In doing so, the research presented also quantifies the actual amount of erosion that has occurred since the formation of the Manicouagan impact structure (>3.5 km) and that distal impact ejecta without a preserved melt component can still be successfully correlated to a crater through heavy mineral correlation techniques.

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Thesis--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (p.133-142)

Cassini spacecraft images of Enceladus' surface have revealed diverse terrains---some heavily cratered, others almost devoid of craters, and even some with ridges and fractures. We have documented crater morphologies in regions for which high-resolution data are available (140 to 360 W and 90 S to 60 N). The south polar region shows a dearth of craters, in sharp contrast to the heavily cratered northern latitudes. Tectonized regions such as Sarandib and Diyar Planitiae also have low crater densities. Viscously relaxed craters are found in the apparently young regions of the anti-Saturnian and trailing hemispheres, as well as in the older, upper northern latitudes. By modeling the viscoelastic relaxation of craters on Enceladus using TEKTON, a finite-element code, we predict large geographical variation in heat flow and a complicated thermal history on Enceladus. Our results are consistent with the planitiae being older examples of the South Polar Terrain, supporting a satellite-reorientation hypothesis.

Understanding the age and distribution of shallow ice on Mars is valuable for interpreting past and present climate conditions, and has implications on habitability and future in situ resource utilization. Many ice-related features, such as lobate debris aprons and concentric crater fill, have been studied using a range of remote sensing techniques. Here, I explore the distribution of expanded craters, a form of sublimation thermokarst where shallow, excess ice has been destabilized and sublimated following an impact event. This leads to the collapse of the overlying dry regolith to produce the appearance of diameter widening. The modern presence of these features suggests that excess ice has remained preserved in the terrain immediately surrounding the craters since the time of their formation in order to maintain the surface. High-resolution imagery is ideal for observing thermokarst features, and much of the work described here will utilize data from the Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO). Expanded craters tend to be found in clusters that emanate radially from at least four primary craters in Arcadia Planitia, and are interpreted as secondary craters that formed nearly simultaneously with their primaries. Crater age dates of the primaries indicate that the expanded secondaries, as well as the ice layer into which they impacted, must be at least tens of millions of years old. Older double-layer ejecta craters in Arcadia Planitia commonly have expanded craters superposed on their ejecta – and they tend to be more expanded (with larger diameters) in the inner ejecta layer. This has implications on the formation mechanisms for craters with this unique ejecta morphology. Finally, I explore the distribution of expanded craters south of Arcadia Planitia and across the southern mid-latitudes, along with scalloped depressions (another form of sublimation thermokarst), in order to identify the modern excess ice boundary in this region and any longitudinal variations. This study identifies some potential low-latitude locations with patchy excess ice, possibly preserved during a past climate. Through these studies, I will infer regions that contain abundant ice today and consider the implications that this ice has on both the martian climate and future exploration.

The North Polar Layered Deposits (NPLD) of Mars contain a complex stratigraphy that has been suggested to retain a record of past eccentricity- and obliquity-forced climate changes. The surface accumulation rate in the current climate can be constrained by the crater retention age. We scale NPLD crater diameters to account for icy target strength and compare surface age using a new production function for recent small impacts on Mars to the previously used model of Hartmann (2005). Our results indicate that ice is accumulating in these craters several times faster than previously thought, with a 100m diameter crater being completely infilled within centuries. Craters appear to have a diameter-dependent lifetime, but the data also permit a complete resurfacing of the NPLD at similar to 1.5 ka.

Abstract Crater counting is a method which allows us to estimate the surface ages of the planetary bodies, from which the sampling and sample delivery to laboratories on Earth are difficult or impossible. Because the number of craters on a surface unit increases over the time the surface has been exposed to space, old, geologically stable units have more craters than young and active units. When the crater production rate as a function of time is known, the absolute age of the surface unit can be determined based on its crater density. The purpose of this thesis is to investigate the role of small impact craters in crater counts to find out how modern very high-resolution space images can be utilized in age determination of planetary surfaces. The thesis focuses on how reliable crater count based datings are, if only small craters and counting areas are used in age determination. The research is carried out by utilizing crater counts on the outflow channels of Dao, Niger, Harmakhis and Reull Valles, which all are located in the eastern rim region of the Hellas impact basin, on the southern hemisphere of Mars. Crater counts are performed mainly based on the images of ConTeXt Imager (CTX) and High Resolution Imaging Science Experiment (HiRISE) aboard Mars Reconnaissance Orbiter (MRO). The results show that small craters are a very valuable tool to get information about the surface age. Instead of the size-range of counted craters, or the size of counting areas, results are dependent on the variability and scale of the surface modification history. The more variable or larger scale the modification history is, the larger surface area and wider crater diameter range are typically needed to achieve comprehensive age estimations. The crater counts on the eastern Hellas outflow channels support the earlier theories according to which the valles formed during a relatively short time interval, ~ 3.4–3.7 Ga ago. The existence of terrace structures and smaller tributary channels indicate that the outflow channels were filled by several pulses of liquids. The major fluvial activity ended no later than ~ 0.8–1.9 Ga ago, and it was probably controlled by the activity of nearby highland volcanoes. Soon after the declined fluvial activity, the outflow channels were covered by ice-rich deposits. The major reason for this was probably the changed climatic conditions, although in places e.g. impact cratering seems to have contributed to the emplacement of the deposits. The region as a whole was also resurfaced several times because of changes in local climate conditions. The most significant of the resurfacing processes seem to be the episodes of thin ice-rich mantling deposits, the most recent of which dominated the regional modification less than 10 Ma ago. In addition, the region has experienced eolian activity during the last 1 Ma. / Original papers The original publications are not included in the electronic version of the dissertation. Kostama, V.-P., Kukkonen, S., & Raitala, J. (2017). Resurfacing event observed in Morpheos basin (Eridania Planitia) and the implications to the formation and timing of Waikato and Reull Valles, Mars. Planetary and Space Science, 140, 35–48. https://doi.org/10.1016/j.pss.2017.04.001 Kukkonen, S., & Kostama, V.-P. (2018). Modification history of the Harmakhis Vallis outflow channel, Mars, based on CTX-scale photogeologic mapping and crater count dating. Icarus, 299, 46–67. https://doi.org/10.1016/j.icarus.2017.07.014 Kukkonen, S., & Kostama, V.-P. (2018). Usability of small impact craters on small surface areas in crater count dating: Analysing examples from the Harmakhis Vallis outflow channel, Mars. Icarus, 305, 33–49. https://doi.org/10.1016/j.icarus.2018.01.004 Kukkonen, S., & Kostama, V.-P. (2018). Mapping and dating based evolution studies of the Niger Vallis outflow channel, Mars. Planetary and Space Science, 153, 54–71. https://doi.org/10.1016/j.pss.2017.12.012 Korteniemi, J., & Kukkonen, S. (2018). Volcanic Structures Within Niger and Dao Valles, Mars, and Implications for Outflow Channel Evolution and Hellas Basin Rim Development. Geophysical Research Letters, 45(7), 2934–2944. https://doi.org/10.1002/2018gl077067 http://jultika.oulu.fi/Record/nbnfi-fe201902226008

Over the last fifty years, our knowledge of the Solar System has increased exponentially. Many planetary surfaces were seen for the first time through spacecraft observations. Yet the interiors of most planetary bodies remain poorly studied. This dissertation focuses on two main topics: the formation of central pit craters and what this reveals about the subsurface volatile content of the target material, and the mantle dynamics of Io and how they relate to the extensive volcanism on its surface. Central pit craters are seen on icy satellites, Mars, the Moon, and Mercury. They have terraced rims, flat floors, and a pit at or near their center. Several formation mechanisms have been suggested. This dissertation assesses the feasibility of central pit crater formation via drainage of impact melt through impact-generated fractures. For impacts on Ganymede, the expected volume of melt and volume of fracture space generated during the impact and the volume of melt able to drain before fractures freeze shut all exceed the observed central pit volumes on Ganymede. This suggests that drainage of impact melt could contribute to central pit crater formation on Ganymede. Molten rock draining through solid rock fractures will freeze shut more rapidly, so this work suggests that impact melt drainage is unlikely to be a significant factor in the formation of central pit craters on rocky bodies unless a significant amount of volatiles are present in the target. Io is the most volcanically active body in the Solar System. While volcanoes are most often associated with plate tectonics on Earth, Io shows no signs of plate tectonics. Previous work has suggested that Io could lose a significant fraction of its internal heat through volcanic eruptions. In this dissertation, I investigate the relationship between mantle convection and magma generation, migration by porous flow, and eruptions on Io. I couple convective scaling laws to a model solving the two-phase flow equations applied to a rising column of mantle. I show that Io has a partially molten upper mantle and loses the majority of its internal heat through volcanic eruption. Next, I present two-dimensional numerical simulations that self-consistently solve the two-phase flow equations including mantle convection and magma generation, migration by porous flow, and eruption. These simulations produce a high heat flux due to volcanic eruption, a thick lithosphere, a partially molten upper mantle, and a high eruption rate—all consistent with observations of Io. This model also reveals the eruption rate oscillates around the statistical steady state average eruption rate suggesting that the eruption rate and total heat flux measurements from the past 35 years may not be representative of Io's long term behavior.

abstract: Lunar Reconnaissance Orbiter (LRO) and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft missions provide new data for investigating the youngest impact craters on Mercury and the Moon, along with lunar volcanic end-members: ancient silicic and young basaltic volcanism. The LRO Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) in-flight absolute radiometric calibration used ground-based Robotic Lunar Observatory and Hubble Space Telescope data as standards. In-flight radiometric calibration is a small aspect of the entire calibration process but an important improvement upon the pre-flight measurements. Calibrated reflectance data are essential for comparing images from LRO to missions like MESSENGER, thus enabling science through engineering. Relative regolith optical maturation rates on Mercury and the Moon are estimated by comparing young impact crater densities and impact ejecta reflectance, thus empirically testing previous models of faster rates for Mercury relative to the Moon. Regolith maturation due to micrometeorite impacts and solar wind sputtering modies UV-VIS-NIR surface spectra, therefore understanding maturation rates is critical for interpreting remote sensing data from airless bodies. Results determined the regolith optical maturation rate on Mercury is 2 to 4 times faster than on the Moon. The Gruithuisen Domes, three lunar silicic volcanoes, represent relatively rare lunar lithologies possibly similar to rock fragments found in the Apollo sample collection. Lunar nonmare silicic volcanism has implications for lunar magmatic evolution. I estimated a rhyolitic composition using morphologic comparisons of the Gruithuisen Domes, measured from NAC 2-meter-per-pixel digital topographic models (DTMs), with terrestrial silicic dome morphologies and laboratory models of viscoplastic dome growth. Small, morphologically sharp irregular mare patches (IMPs) provide evidence for recent lunar volcanism widely distributed across the nearside lunar maria, which has implications for long-lived nearside magmatism. I identified 75 IMPs (100-5000 meters in dimension) in NAC images and DTMs, and determined stratigraphic relationships between units common to all IMPs. Crater counts give model ages from 18-58 Ma, and morphologic comparisons with young lunar features provided an additional age constraint of <100 Ma. The IMPs formed as low-volume basaltic eruptions significantly later than previous evidence of lunar mare basalt volcanism's end (1-1.2 Ga). / Dissertation/Thesis / Ph.D. Geological Sciences 2013

The Siljan Ring in Dalarna, Sweden is the site of the largest meteor impact crater in Europe and has long been a topic of discussion regarding methane production. However, the source of this methane and the timing of production in relation to the impact remain unclear. An outcrop of red Ordovician limestone preserved on the edge of a downfaulted zone encircling the crater’s central plateau is crosscut by fractures surrounded by pale-coloured reduction haloes within which precipitates can be observed. These haloes suggest interaction with a reducing agent mobilised within a fluid flow, of which methane would be a prime candidate. A field study was subsequently undertaken to establish the reaction whereby these haloes were formed, as well as the timing of their formation relative to the Siljan impact based upon petrological, geochemical, and structural data obtained in the field. Results from this study show that a methane-bearing hydrothermal fluid mobilised within the fractures has preserved the original mineralogy of the limestone within the reaction haloes whilst the country rock beyond was being oxidised. Pyrite is shown to be preserved within the pale reaction haloes, whilst its oxidation within the country rock is shown to be the source of the limestone’s distinct red colouring. Fracture and bedding orientation at the study site suggest the hydrothermal event to have been simultaneous with the meteor impact, with the fractures forming part of a wider complex network of impact features. Whilst mobilisation associated with the meteor impact is a likely cause of methane release, the exact source of the methane active at the study site is unclear.