Veronica Josefine Bray Durfey

Interests

Teaching

Astrobiology PTYS214

Research

Developing of spacecraft instrumentation for landed missions throughout the solar system.Impact craters, their environmental effects, and discovery with remote sensing. Analysis of crater morphology and impact melt generation across the solar system as a means to compare the surface and subsurface properties of planetary bodies. Recreation of cratering with numerical models, and the development of suitable strength models and equations of state to approximate a variety of planetary crusts. 

Courses

Scholarly Contributions

Journals/Publications

• Ballouz, R. -., Agrusa, H., Barnouin, O., Walsh, K., Zhang, Y., Binzel, R., Bray, V., DellaGiustina, D., Jawin, E., DeMartini, J., Marusiak, A., Michel, P., Murdoch, N., Richardson, D., Rivera-Valent{\'\in}, E., Rivkin, A., & Tang, Y. (2024). Shaking and Tumbling: Short- and Long-timescale Mechanisms for Resurfacing of Near-Earth Asteroid Surfaces from Planetary Tides and Predictions for the 2029 Earth Encounter by (99942) Apophis. \psj, 5(11), 251.
• Bland, M. T., & Bray, V. J. (2024). The inevitability of large shallow craters on Callisto and Ganymede: Implications for crater depth-diameter trends. \icarus, 408, 115811.
• Bray, V., & Schenk, P. (2024). Crater Morphometry on Callisto. \psj, 5(8), 188.
• Bray, V., Schenk, P., Melosh, H., Morgan, J., & Collins, G. (2024). Corrigendum to ``Ganymede crater dimensions - Implications for central peak and central pit formation and development'' [Icarus (2012) 115-129]. \icarus, 407, 115799.
• DellaGiustina, D., Ballouz, R. -., Walsh, K., Marusiak, A., Bray, V., & Bailey, S. (2024). Seismology of rubble-pile asteroids in binary systems. \mnras, 528(4), 6568-6580.
• Fraser, W. C., Porter, S. B., Peltier, L., Kavelaars, J. J., Verbiscer, A. J., Buie, M. W., Stern, S. A., Spencer, J. R., Benecchi, S. D., Terai, T., Ito, T., Yoshida, F., Gerdes, D. W., Napier, K. J., Lin, H. W., Gwyn, S. D., Smotherman, H., Fabbro, S., Singer, K. N., , Alexander, A. M., et al. (2024). Candidate Distant Trans-Neptunian Objects Detected by the New Horizons Subaru TNO Survey. \psj, 5(10), 227.
• McEwen, A., Byrne, S., Hansen, C., Daubar, I., Sutton, S., Dundas, C., Bardabelias, N., Baugh, N., Bergstrom, J., Beyer, R., Block, K., Bray, V., Bridges, J., Chojnacki, M., Conway, S., Delamere, W., Ebben, T., Espinosa, A., Fennema, A., , Grant, J., et al. (2024). The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009\textendash2023). \icarus, 419, 115795.
• Nicholson, U., Powell, W., Gulick, S., Kenkmann, T., Bray, V. J., Duarte, D., & Collins, G. S. (2024). 3D anatomy of the Cretaceous\textendashPaleogene age Nadir Crater. Communications Earth and Environment, 5(1), 547.
• Hedgepeth, J. E., Neish, C. D., & Bray, V. J. (2023). Impact Crater Morphometry on Pluto: Implications for Surface Composition and Evolution. \psj, 4(10), 190.
• Leiva, R., Spencer, J., Lauer, T., Benecchi, S., Singer, K., Glass, F., Skrutskie, M., Alexander, A., Hong, P., Reitsema, H., Lin, E., Lykawka, P., Ito, T., Marschall, R., Simpson, A., Banks, M., Ishimaru, R., Holt, T., Postman, M., , Olkin, C., et al. (2023). 2013 LU35. Minor Planet Electronic Circulars, 2023-F108.
• Leiva, R., Spencer, J., Lauer, T., Benecchi, S., Singer, K., Glass, F., Skrutskie, M., Alexander, A., Hong, P., Reitsema, H., Lin, E., Lykawka, P., Ito, T., Marschall, R., Simpson, A., Banks, M., Ishimaru, R., Holt, T., Postman, M., , Olkin, C., et al. (2023). 2014 MH105. Minor Planet Electronic Circulars, 2023-U28.
• Leiva, R., Spencer, J., Lauer, T., Benecchi, S., Singer, K., Glass, F., Skrutskie, M., Alexander, A., Hong, P., Reitsema, H., Lin, E., Lykawka, P., Ito, T., Marschall, R., Simpson, A., Banks, M., Ishimaru, R., Holt, T., Postman, M., , Olkin, C., et al. (2023). 2014 PN70. Minor Planet Electronic Circulars, 2023-F106.
• Leiva, R., Spencer, J., Lauer, T., Benecchi, S., Singer, K., Glass, F., Skrutskie, M., Alexander, A., Hong, P., Reitsema, H., Lin, E., Lykawka, P., Ito, T., Marschall, R., Simpson, A., Banks, M., Ishimaru, R., Holt, T., Postman, M., , Olkin, C., et al. (2023). 2021 LD44. Minor Planet Electronic Circulars, 2023-F109.
• Leiva, R., Spencer, J., Lauer, T., Benecchi, S., Singer, K., Glass, F., Skrutskie, M., Alexander, A., Hong, P., Reitsema, H., Lin, E., Lykawka, P., Ito, T., Marschall, R., Simpson, A., Banks, M., Ishimaru, R., Holt, T., Postman, M., , Olkin, C., et al. (2023). 2021 LP44. Minor Planet Electronic Circulars, 2023-F110.
• Leiva, R., Spencer, J., Lauer, T., Benecchi, S., Singer, K., Glass, F., Skrutskie, M., Alexander, A., Hong, P., Reitsema, H., Lin, E., Lykawka, P., Ito, T., Marschall, R., Simpson, A., Banks, M., Ishimaru, R., Holt, T., Postman, M., , Olkin, C., et al. (2023). Six New Tnos. Minor Planet Electronic Circulars, 2023-F132.
• Rae, A., & Bray, V. (2023). Effects on Target Geology. EarthArXiv eprints, X5H97T.
• Avenson, B., Bailey, S. H., Bray, V. J., Brodbeck, J. I., Carr, C. G., Dahl, P. H., Dellagiustina, D. N., Habib, N., Marusiak, A. G., Pettit, E. C., Schmerr, N. C., Wagner, N., & Weber, R. C. (2021). The Deployment of the Seismometer to Investigate Ice and Ocean Structure (SIIOS) in Northwest Greenland: An Analog Experiment for Icy Ocean World Seismic Deployments. Seismological Research Letters, 92(3), 2036-2049. doi:10.1785/0220200291
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  Abstract In anticipation of future spacecraft missions to icy ocean worlds, the Seismometer to Investigate Ice and Ocean Structure (SIIOS) was funded by National Aeronautics and Space Administration, to prepare for seismologic investigations of these worlds. During the summer of 2018, the SIIOS team deployed a seismic experiment on the Greenland ice sheet situated, approximately, 80 km north of Qaanaaq, Greenland. The seismometers deployed included one Trillium 120 s Posthole (TPH) broadband seismometer, 13 Silicon Audio flight-candidate seismometers, and five Sercel L28 4.5 Hz geophones. Seismometers were buried 1 m deep in the firn in a cross-shaped array centered on a collocated TPH and Silicon Audio instrument. One part of the array consisted of Silicon Audio and Sercel geophones situated 1 m from the center of the array in the ordinal directions. A second set of four Silicon Audio instruments was situated 1 km from the center of the array in the cardinal directions. A mock-lander spacecraft was placed at the array center and instrumented with four Silicon Audio seismometers. We performed an active-source experiment and a passive-listening experiment that lasted for, approximately, 12 days. The active–source experiment consisted of 9–12 sledgehammer strikes to an aluminum plate at 10 separate locations up to 100 m from the array center. The passive experiment recorded the ice-sheet ambient background noise, as well as local and regional events. Both datasets will be used to quantify differences in spacecraft instrumentation deployment strategies, and for evaluating science capabilities for single-station and small-aperture seismic arrays in future geophysical missions. Our initial results indicate that the flight-candidate seismometer performs comparably to the TPH at frequencies above 0.1 Hz and that instruments coupled to the mock-lander perform comparably to ground-based instrumentation in the frequency band of 0.1–10 Hz. For future icy ocean world missions, a deck-coupled seismometer would perform similarly to a ground-based deployment across the most frequency bands.
• Beddingfield, C. B., Beyer, R. A., Binzel, R. P., Bray, V. J., Parker, A. H., Riggs, J. D., Robbins, S. J., Runyon, K. D., Schenk, P. M., & Verbiscer, A. J. (2021). Depths of Pluto's and Charon's craters, and their simple-to-complex transition. Icarus, 356, 113902. doi:10.1016/j.icarus.2020.113902
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  Abstract Impact craters form as point-like explosions on solar system bodies, excavating a cavity within the surface. Most information about the impactor itself is lost, save its energy, such that the target itself controls much of the final crater size and shape given the energy input. For this reason, impact craters are a useful probe of surface differences across a single body and between bodies. Two properties that are commonly used to compare craters from one body to another are the ratio between crater depth and diameter, and the diameter at which craters transition between simple, bowl-shaped morphologies to more complex morphologies that include flat floors, central peaks, wall terraces, and scalloped rims. Both metrics are important as input into theoretical models and for probing the strength of the surface material. In this work, we have measured these properties on Pluto and Charon and report on the results. However, the analysis is not entirely straightforward; a secondary goal of this work is to explore how to measure and quantify the two properties accurately (depth vs diameter and simple-to-complex transitions). We arrive at different results based on the method, and we report on that variation as a way to reasonably estimate the uncertainty in each quantity. For those reasons, it is difficult to place a single, exact value on each, but we do conclude that the morphology-based simple-to-complex transition occurs at approximately 11–12½ km on Pluto, and 13½–16 km on Charon. We also conclude that the existing, public topography data for at least Charon is likely too low in resolution to measure the simple crater depth vs diameter function accurately, such that a morphometry-based simple-to-complex transition diameter is not quantifiable at this time.
• Bland, M. T., Bray, V. J., Buczkowski, D. L., Castillo-rogez, J., Corre, L. L., Hiesinger, H., Hoogenboom, T., Hughson, K., Kramer, G. Y., Krohn, K., Marchi, S., Mcfadden, L. A., Neesemann, A., O'brien, D. P., Otto, K. A., Platz, T., Raymond, C. A., Russell, C. T., Sanctis, M. C., , Schenk, P. M., et al. (2021). Compositional control on impact crater formation on mid-sized planetary bodies: Dawn at Ceres and Vesta, Cassini at Saturn. Icarus, 359, 114343. doi:10.1016/j.icarus.2021.114343
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  Abstract High-resolution mapping of Ceres, Vesta and the icy satellites of Saturn, Uranus and Pluto reveals a rich variety of well-preserved impact crater morphologies on these low gravity bodies. These objects provide a natural laboratory to study effects of composition on crater formation processes under similar surface gravity conditions (though mean impact velocities vary by several factors). Simple craters occur on all these bodies but subtle differences in morphology on Ceres and Vesta are recognized. Immature complex craters (with large floor mounds but not terraces or conical central peaks) occur on Vesta and while smaller than predicted are consistent with its silicate composition. Asymmetric simple craters (with incomplete scarp development) on all bodies are likely related to differential overburden stresses in the rim, and their occurrence is consistent with lower crustal strength on icy bodies including Ceres. Immature and mature complex craters exhibit increasing degrees of complexity, including spiral floor deformation patterns (related to failure in converging floor material), central peaks, and impact melt. Cerean crater morphologic types and simple-complex transition diameters are smaller than on Vesta but similar to those on icy satellites, indicating a much weaker rheology for Ceres' outer layers under impact conditions. These are consistent with geophysical indications of a low-density water ice and probably clathrate rich outer shell. Fluidized floor deposits (impact melt or melt-solid mixtures) are significant in craters >25 km across on Ceres but absent on Saturn satellites. Central pit craters are common on Ceres (at diameters of ~75 to 150 km consistent with gravity scaling from the larger Galilean satellites) but are absent on Saturnian satellites and Charon. The contrasting impact melt and central pit behaviors on Ceres and Saturn's moons is contrary to expectation given the higher impact velocities at Saturn but might be related to lower internal temperatures, or the higher fraction of non-ice material on Ceres. The correlation or scaling of transition diameters to surface gravity is near −0.65 rather than −1, perhaps due to increased porosity on lower gravity bodies. The fundamental similarity of crater morphologies on Ceres and icy satellites, however, indicates that the weaker rheology of water ice results in similar craters even if the non-(ice+clathrate) components are as high as ~30 vol%.
• Avenson, B., Bailey, H., Bray, V. J., Broadbeck, J. I., Dellagiustina, D., Gardner, C., Habib, N., Maguire, R., Marusiak, A. G., Pettit, E. C., Riverman, K., Schmerr, N., & Wagner, N. (2020). Geophysical constraints on the properties of a subglacial lake innorthwest Greenland. The Cryosphere Discussions, 1-19. doi:10.5194/tc-2020-321
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  Abstract. We report the first ground-based observations of a subglacial lake in Greenland, confirming previous work base on airborne radar data. Here, we perform an active source seismology and ground penetrating radar survey in northwest Greenland where Palmer et al. (2013) first proposed the presence of a subglacial lake. From reflections of both the lake top and lake bottom, we observe a subglacial lake underlying approximately 845 m of ice, and constrain its depth to be between 10–15 m. Additionally, using previously reported estimates of the lake's lateral extent, we estimate the total volume of liquid water to be 0.15 km3 (0.15 Gt of water). Thermal and hydropotential modeling both suggest that the lake should not exist unless it either sits over a localized geothermal flux high or has high salinity due to significant evaporite source in the bedrock. Our study indicates that this field site in northwestern Greenland is a good candidate for future investigations aimed at understanding lake properties and origins or for direct lake sampling via drilling.
• Beddingfield, C. B., Beyer, R. A., Singer, K. N., Mckinnon, W. B., Runyon, K., Stern, S. A., Moore, J. M., Ennico, K., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Bray, V. J., Dhingra, R. D., Grundy, W. M., Schenk, P. M., & Team, N. H. (2020). Landslides on Charon. Icarus, 335, 113383. doi:10.1016/j.icarus.2019.07.017
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  Abstract We investigated five large landslides identified in the Serenity Chasma region of Charon. The identification of these landslides involved a search for these features in images taken by cameras onboard the New Horizons spacecraft. Various landslide properties were analyzed based on their morphologies using a digital terrain model of the region. We found that landslides are confined to the walls of the large normal fault scarps that make up Serenity Chasma. Based on extensive landslide runout lengths (L) relative to their drop heights (H), we classified these features as long-runout landslides. By analyzing their geometries, we estimated the friction coefficients of the landslide material (H/L) to be between 0.15 to 0.31 and the runout efficiencies (L/H) to be between 3.2 and 6.8. We also estimated that the specific energy released during landslide motion ranged from 0.8 to 1.3 kJ kg−1. These amounts of energy were too low to have generated significant melt around landslide particles.
• Marusiak, A. G., Schmerr, N. C., Dellagiustina, D. N., Pettit, E. C., Dahl, P. H., Avenson, B., Bailey, S. H., Bray, V. J., Wagner, N., Carr, C. G., & Weber, R. C. (2020). The Deployment of the Seismometer to Investigate Ice and Ocean Structure (SIIOS) on Gulkana Glacier, Alaska. Seismological Research Letters, 91(3), 1901-1914. doi:10.1785/0220190328
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  AbstractThe Seismometer to Investigate Ice and Ocean Structure (SIIOS) is a NASA-funded analog mission program to test flight-candidate instrumentation on icy-ocean world analog sites. In September 2017, an SIIOS experiment was deployed on Gulkana Glacier. The instrumentation included a Nanometrics Trillium 120 s Posthole seismometer, four Nanometrics Trillium Compact (TC) seismometers, four Mark Products L28 geophones, and five each of Silicon Audio (SiA) 203P-15 and 203P-60 seismometers. The SiA sensors served as our flight-candidate instruments. The instrumentation was arranged in a small (6.0. The active- and passive-source signals are being used to constrain the local glacial hydrological structure, environmental seismicity, to develop algorithms to detect and locate seismic sources, and to quantify the similarities and differences in science capabilities between sensors. Initial results indicate the flight-candidate instrumentation performs comparably to the Trillium Posthole up to periods of 3 s, after which the flight-candidate performs more comparably to the TCs.
• Spencer, J. R., Stern, S. A., Moore, J. M., Weaver, H. A., Singer, K. N., Olkin, C. B., Verbiscer, A. J., Mckinnon, W. B., Parker, J. W., Beyer, R. A., Keane, J. T., Lauer, T. R., Porter, S. B., White, O. L., Buratti, B. J., El-maarry, M. R., Lisse, C. M., Parker, A. H., Throop, H. B., , Robbins, S. J., et al. (2020). The geology and geophysics of Kuiper Belt object (486958) Arrokoth.. Science (New York, N.Y.), 367(6481), eaay3999. doi:10.1126/science.aay3999
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  The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.
• Brandt, P., Mcnutt, R., Grava, C., Russell, C. T., Szalay, J. R., Colwell, J., Kotova, A., Achterberg, R. K., Allegrini, F., Allen, R., Andre, N., Arridge, C. S., Aslam, S., Azari, A., Baines, K. H., Barnes, J. W., Bergman, J., Brandt, P. C., Bray, V. J., , Bunce, E. J., et al. (2019). Solar System Ice Giants: Exoplanets in our Backyard.. Bulletin of the American Astronomical Society, 51(3).
• Bray, V. J., Henning, W. G., Hurford, T. A., Kattenhorn, S. A., Lekic, V., Maguire, R., Manga, M., Panning, M. P., Quick, L. C., Rhoden, A. R., & Schmerr, N. (2019). Seismicity on tidally active solid-surface worlds.. Icarus, 338, 113466. doi:10.1016/j.icarus.2019.113466
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  Tidal interactions between planets or stars and the bodies that orbit them dissipate energy in their interiors. The dissipated energy heats the interior and a fraction of that energy will be released as seismic energy. Here we formalize a model to describe the tidally-driven seismic activity on planetary bodies based on tidal dissipation. To constrain the parameters of our model we use the seismic activity of the Moon, driven by tidal dissipation from the Earth-Moon interactions. We then apply this model to predict the amount of seismic energy release and largest seismic events on other moons in our Solar System and exoplanetary bodies. We find that many moons in the Solar System should be more seismically active than the Earth's Moon and many exoplanets should exhibit more seismic activity than the Earth. Finally, we examine how temporal-spatial variations in tidal dissipation manifest as variations in the locations and timing of seismic events on these bodies.
• Cruikshank, D. P., Materese, C. K., Pendleton, Y. J., Boston, P. J., Grundy, W. M., Schmitt, B., Lisse, C. M., Runyon, K. D., Keane, J. T., Beyer, R. A., Summers, M. E., Scipioni, F., Stern, S. A., Ore, C. M., Olkin, C. B., Young, L. A., Ennico, K., Weaver, H. A., & Bray, V. J. (2019). Prebiotic Chemistry of Pluto.. Astrobiology, 19(7), 831-848. doi:10.1089/ast.2018.1927
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  We present the case for the presence of complex organic molecules, such as amino acids and nucleobases, formed by abiotic processes on the surface and in near-subsurface regions of Pluto. Pluto's surface is tinted with a range of non-ice substances with colors ranging from light yellow to red to dark brown; the colors match those of laboratory organic residues called tholins. Tholins are broadly characterized as complex, macromolecular organic solids consisting of a network of aromatic structures connected by aliphatic bridging units (e.g., Imanaka et al., 2004; Materese et al., 2014, 2015). The synthesis of tholins in planetary atmospheres and in surface ices has been explored in numerous laboratory experiments, and both gas- and solid-phase varieties are found on Pluto. A third variety of tholins, exposed at a site of tectonic surface fracturing called Virgil Fossae, appears to have come from a reservoir in the subsurface. Eruptions of tholin-laden liquid H2O from a subsurface aqueous repository appear to have covered portions of Virgil Fossae and its surroundings with a uniquely colored deposit (D.P. Cruikshank, personal communication) that is geographically correlated with an exposure of H2O ice that includes spectroscopically detected NH3 (C.M. Dalle Ore, personal communication). The subsurface organic material could have been derived from presolar or solar nebula processes, or might have formed in situ. Photolysis and radiolysis of a mixture of ices relevant to Pluto's surface composition (N2, CH4, CO) have produced strongly colored, complex organics with a significant aromatic content having a high degree of nitrogen substitution similar to the aromatic heterocycles pyrimidine and purine (Materese et al., 2014, 2015; Cruikshank et al., 2016). Experiments with pyrimidines and purines frozen in H2O-NH3 ice resulted in the formation of numerous nucleobases, including the biologically relevant guanine, cytosine, adenine, uracil, and thymine (Materese et al., 2017). The red material associated with the H2O ice may contain nucleobases resulting from energetic processing on Pluto's surface or in the interior. Some other Kuiper Belt objects also exhibit red colors similar to those found on Pluto and may therefore carry similar inventories of complex organic materials. The widespread and ubiquitous nature of similarly complex organic materials observed in a variety of astronomical settings drives the need for additional laboratory and modeling efforts to explain the origin and evolution of organic molecules. Pluto observations reveal complex organics on a small body that remains close to its place of origin in the outermost regions of the Solar System.
• Robbins, S. J., Beyer, R. A., Spencer, J. R., Grundy, W. M., White, O. L., Singer, K. N., Moore, J. M., Ore, C. M., Mckinnon, W. B., Lisse, C. M., Runyon, K., Beddingfield, C. B., Umurhan, O. M., Cruikshank, D. P., Lauer, T. R., Bray, V. J., Binzel, R. P., Buie, M. W., Buratti, B. J., , Cheng, A. F., et al. (2019). Geologic Landforms and Chronostratigraphic History of Charon as Revealed by a Hemispheric Geologic Map. Journal of Geophysical Research, 124(1), 155-174. doi:10.1029/2018je005684
• Singer, K. N., Mckinnon, W. B., Greenstreet, S., Bierhaus, E. B., Stern, S. A., Parker, A. H., Robbins, S. J., Schenk, P. M., Grundy, W. M., Bray, V. J., Beyer, R. A., Binzel, R. P., Weaver, H. A., Young, L. A., Spencer, J. R., Kavelaars, J. J., Moore, J. M., Zangari, A. M., Olkin, C. B., , Lauer, T. R., et al. (2019). Impact craters on Pluto and Charon indicate a deficit of small Kuiper belt objects.. Science (New York, N.Y.), 363(6430), 955-959. doi:10.1126/science.aap8628
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  The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters ≲13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (≲1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely ≳4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.
• Stern, S. A., Weaver, H. A., Spencer, J. R., Olkin, C. B., Gladstone, G. R., Grundy, W. M., Moore, J. M., Cruikshank, D. P., Elliott, H. A., Mckinnon, W. B., Parker, J. W., Verbiscer, A. J., Young, L. A., Aguilar, D. A., Albers, J. M., Andrews, J. P., Bagenal, F., Banks, M. E., Bauer, B. A., , Bauman, J. A., et al. (2019). Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper Belt object.. Science (New York, N.Y.), 364(6441), eaaw9771. doi:10.1126/science.aaw9771
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  The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69's origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.
• Benecchi, S. D., Beyer, R. A., Binzel, R. P., Bray, V. J., Buie, M. W., Buratti, B. J., Chavez, C. L., Cheng, A. F., Cruikshank, D. P., Dhingra, R. D., Gladstone, G. R., Grundy, W. M., Howard, A. D., Howett, C., Lauer, T. R., Lisse, C. M., Mckinnon, W. B., Moore, J. M., Olkin, C. B., , Parker, A. H., et al. (2018). Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU 69 ("Ultima Thule"). Geophysical Research Letters, 45(16), 8111-8120. doi:10.1029/2018gl078996
• Bray, V. J., Artemieva, N. A., Atwood-stone, C., Mcelwaine, J. N., Mcewen, A. S., & Neish, C. D. (2018). Lobate impact melt flows within the extended ejecta blanket of Pierazzo crater. Icarus, 301, 26-36. doi:10.1016/j.icarus.2017.10.002
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  Abstract Impact melt flows are observed within the continuous and discontinuous ejecta blanket of the 9 km lunar crater Pierazzo, from the crater rim to more than 40 km away from the center of the crater. Our mapping, fractal analysis, and thermal modeling suggest that melt can be emplaced ballistically and, upon landing, can become separated from solid ejecta to form the observed flow features. Our analysis is based on the identification of established melt morphology for these in-ejecta flows and supported by fractal analysis and thermal modeling. We computed the fractal dimension for the flow boundaries and found values of D = 1.05–1.17. These are consistent with terrestrial basaltic lava flows (D = 1.06–1.2) and established lunar impact melt flows (D = 1.06–1.18), but inconsistent with lunar dry granular flows (D = 1.31–1.34). Melt flows within discontinuous ejecta deposits are noted within just 1.5% of the mapping area, suggesting that the surface expression of impact melt in the extended ejecta around craters of this size is rare, most likely due to the efficient mixing of melts with solid ejecta and local target rocks. However, if the ejected fragments (both, molten and solid) are large enough, segregation of melt and its consequent flow is possible. As most of the flows mapped in this work occur on crater-facing slopes, the development of defined melt flows within ejecta deposits might be facilitated by high crater-facing topography restricting the flow of ejecta soon after it makes ground contact, limiting the quenching of molten ejecta through turbulent mixing with solid debris. Our study confirms the idea that impact melt can travel far beyond the continuous ejecta blanket, adding to the lunar regolith over an extensive area.
• Robbins, S. J., Runyon, K., Singer, K. N., Bray, V. J., Beyer, R. A., Mckinnon, W. B., Grundy, W. M., Nimmo, F., Moore, J. M., Spencer, J. R., White, O. L., Binzel, R. P., Buie, M. W., Buratti, B. J., Cheng, A. F., Linscott, I. R., Reitsema, H. J., Reuter, D. C., Showalter, M. R., , Tyler, G. L., et al. (2018). Investigation of Charon's Craters With Abrupt Terminus Ejecta, Comparisons With Other Icy Bodies, and Formation Implications. Journal of Geophysical Research, 123(1), 20-36. doi:10.1002/2017je005287
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  NASA's New Horizons mission within the New Frontiers program; NASA's Mars Data Analysis Program [NNX15AM48G]
• Robbins, S. J., Watters, W. A., Chappelow, J. E., Bray, V. J., Daubar, I. J., Craddock, R. A., Beyer, R. A., Ostrach, L. R., Riggs, J. D., Weaver, B. P., Landis, M. E., & Tornabene, L. L. (2018). Measuring impact crater depth throughout the solar system. Meteoritics & Planetary Science, 53(4), 583-637. doi:10.1111/maps.12956
• Robbins, S. J., Singer, K. N., Bray, V. J., Lauer, T. R., Weaver, H. A., Runyon, K., Mckinnon, W. B., Beyer, R. A., White, O. L., Hofgartner, J. D., Zangari, A. M., Moore, J. M., Young, L. A., Spencer, J. R., Binzel, R. P., Buie, M. W., Buratti, B. J., Cheng, A. F., Grundy, W. M., , Linscott, I. R., et al. (2017). Craters of the Pluto-Charon System. Icarus, 287, 187-206. doi:10.1016/j.icarus.2016.09.027
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  Abstract NASA's New Horizons flyby mission of the Pluto-Charon binary system and its four moons provided humanity with its first spacecraft-based look at a large Kuiper Belt Object beyond Triton. Excluding this system, multiple Kuiper Belt Objects (KBOs) have been observed for only 20 years from Earth, and the KBO size distribution is unconstrained except among the largest objects. Because small KBOs will remain beyond the capabilities of ground-based observatories for the foreseeable future, one of the best ways to constrain the small KBO population is to examine the craters they have made on the Pluto-Charon system. The first step to understanding the crater population is to map it. In this work, we describe the steps undertaken to produce a robust crater database of impact features on Pluto, Charon, and their two largest moons, Nix and Hydra. These include an examination of different types of images and image processing, and we present an analysis of variability among the crater mapping team, where crater diameters were found to average ± 10% uncertainty across all sizes measured (∼0.5–300 km). We also present a few basic analyses of the crater databases, finding that Pluto's craters' differential size-frequency distribution across the encounter hemisphere has a power-law slope of approximately –3.1 ± 0.1 over diameters D ≈ 15–200 km, and Charon's has a slope of –3.0 ± 0.2 over diameters D ≈ 10–120 km; it is significantly shallower on both bodies at smaller diameters. We also better quantify evidence of resurfacing evidenced by Pluto's craters in contrast with Charon's. With this work, we are also releasing our database of potential and probable impact craters: 5287 on Pluto, 2287 on Charon, 35 on Nix, and 6 on Hydra.
• White, O. L., Schenk, P. M., Bellagamba, A. W., Grimm, A. M., Dombard, A. J., & Bray, V. J. (2017). Impact crater relaxation on Dione and Tethys and relation to past heat flow. Icarus, 288, 37-52. doi:10.1016/j.icarus.2017.01.025
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  Abstract Relating relaxation of impact crater topography to past heat flow through the crusts of icy satellites is a technique that has been applied to satellites around Jupiter and Saturn. We use global digital elevation models of the surfaces of Dione and Tethys generated from Cassini data to obtain crater depth/diameter ( d/D ) data. Relaxation is found to affect craters down to smaller diameters on these satellites compared to Rhea. We perform relaxation simulations in order to assess the heat flow necessary to relax craters on Dione and Tethys to their present morphologies. Heat flows exceeding 60 mW m −2 are required to relax several craters on both satellites, and relaxation appears to be subject to geographical controls. On Dione, we define a ‘relaxation dichotomy’ that separates the more relaxed craters in sparsely cratered plains from the less relaxed craters in heavily cratered terrain. The configuration of this dichotomy resembles that of the structural-geological dichotomy on Enceladus, implying that a similar resonance-induced tidal heating mechanism concentrated in the southern hemisphere may have affected both satellites. Defining geographical distribution of relaxation on Tethys is hindered by the presence of the young Odysseus impact and its associated ejecta.
• Bray, V. J., Atwood-stone, C., & Mcewen, A. S. (2016). A new study of crater concentric ridges on the Moon. Icarus, 273, 196-204. doi:10.1016/j.icarus.2016.03.012
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  Abstract Crater concentric ridges (CCRs) are topographic ridges found in the ejecta blankets of fresh few-kilometer-scale lunar craters. These ridges, which were last studied in detail in the late 1970 s (referred to as ‘lunar concentric dunes’), were hypothesized to form due to ballistic impact sedimentation and erosion. We have surveyed the Moon to find 59 craters with CCRs and have constructed mosaics of these craters where possible using high-resolution LROC NAC (Lunar Reconnaissance Orbiter Camera—Narrow Angle Camera) images. We then map from some of these mosaics in order to measure the CCRs and examine their morphologies. Ejecta scaling models and some of our observations of the CCRs contradict the current hypothesis for the formation of these features. We therefore propose new hypotheses to consider for the formation of CCRs, specifically interaction of ejecta with initial topography or formation via interactions of shocks in the ejecta. Additionally, for the first time we have found CCRs on Mercury, but they are rare or absent on Mars.
• Grundy, W. M., Cruikshank, D. P., Gladstone, G. R., Howett, C. J., Lauer, T. R., Spencer, J. R., Summers, M. E., Buie, M. W., Earle, A. M., Ennico, K., Parker, J. W., Porter, S. B., Singer, K. N., Stern, S. A., Verbiscer, A. J., Beyer, R. A., Binzel, R. P., Buratti, B. J., Cook, J. C., , Ore, C. M., et al. (2016). The formation of Charon's red poles from seasonally cold-trapped volatiles.. Nature, 539(7627), 65-68. doi:10.1038/nature19340
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  A unique feature of Pluto's large satellite Charon is its dark red northern polar cap. Similar colours on Pluto's surface have been attributed to tholin-like organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location on Charon implicates the temperature extremes that result from Charon's high obliquity and long seasons in the production of this material. The escape of Pluto's atmosphere provides a potential feedstock for a complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon's winter pole was proposed as an explanation for the dark coloration on the basis of an image of Charon's northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase that show the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon and the supply and temporary cold-trapping of material escaping from Pluto, as well as the photolytic processing of this material into more complex and less volatile molecules while cold-trapped. The model results are consistent with the proposed mechanism for producing the observed colour pattern on Charon.
• Moore, J. M., Mckinnon, W. B., Spencer, J. R., Howard, A. D., Schenk, P. M., Beyer, R. A., Nimmo, F., Singer, K. N., Umurhan, O. M., White, O. L., Stern, S. A., Ennico, K., Olkin, C. B., Weaver, H. A., Young, L. A., Binzel, R. P., Buie, M. W., Buratti, B. J., Cheng, A. F., , Cruikshank, D. P., et al. (2016). The geology of Pluto and Charon through the eyes of New Horizons.. Science (New York, N.Y.), 351(6279), 1284-93. doi:10.1126/science.aad7055
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  NASA's New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Pluto's encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than ~10 million years. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, the latter likely caused by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest impactor size-frequency distributions proposed for the Kuiper belt.
• Neish, C. D., Molaro, J. L., Lora, J. M., Howard, A. D., Kirk, R. L., Bray, V. J., Lorenz, R. D., & Schenk, P. M. (2016). Fluvial erosion as a mechanism for crater modification on Titan. Icarus, 270, 114-129. doi:10.1016/j.icarus.2015.07.022
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  Abstract There are few identifiable impact craters on Titan, especially in the polar regions. One explanation for this observation is that the craters are being destroyed through fluvial processes, such as weathering, mass wasting, fluvial incision and deposition. In this work, we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on Titan. We find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as Cassini, given enough time and a large enough erosion rate. A difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in Titan’s crater population. Fluvial erosion also removes central peaks and fills in central pits, possibly explaining their infrequent occurrence in Titan craters. Although many craters on Titan appear to be modified by aeolian infilling, fluvial modification is necessary to explain the observed impact crater morphologies. Thus, it is an important secondary modification process even in Titan’s drier equatorial regions.
• Weaver, H. A., Buie, M. W., Buratti, B. J., Grundy, W. M., Lauer, T. R., Olkin, C. B., Parker, A. H., Porter, S. B., Showalter, M. R., Spencer, J. R., Stern, S. A., Verbiscer, A. J., Mckinnon, W. B., Moore, J. M., Robbins, S. J., Singer, K. N., Barnouin, O. S., Cheng, A. F., Ernst, C. M., , Lisse, C. M., et al. (2016). The small satellites of Pluto as observed by New Horizons.. Science (New York, N.Y.), 351(6279), aae0030. doi:10.1126/science.aae0030
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  The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of ~40 kilometers for Nix and Hydra and ~10 kilometers for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of ~2. All four moons have high albedos (~50 to 90%) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages of at least 4 billion years. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary.
• Bray, V. J., & Schenk, P. M. (2015). Pristine impact crater morphology on Pluto – Expectations for New Horizons. Icarus, 246, 156-164. doi:10.1016/j.icarus.2014.05.005
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  Abstract This paper combines previous cratering studies and numerical modeling of the impact process at different impact velocities to predict crater morphology on Pluto. As an icy body, Pluto’s craters are expected to be similar in morphology to those on the icy satellites: lesser depth–diameter ratios ( d / D ), shallower wall slopes and the development of central uplifts in craters of smaller rim-to-rim diameter than craters on rocky bodies of similar gravity. The low impact velocity of the Pluto system (∼2 km s −1 ) might cause deviation from this generalization as the simulations presented in this work suggest that decreasing impact velocity from 10 km s −1 to 2 km s −1 results in deeper craters (larger d / D ) and a simple-to-complex transition diameter at larger crater sizes than predicted based on gravity scaling alone ( D > 6 km). Conversely, decreasing impact velocity from 2 km s −1 to 300 m s −1 produced smaller d / D , akin to the lower d / D noted for secondary craters. This complex relationship between impact velocity and d / D suggests that there might be a larger range of ‘pristine’ simple crater depths on Pluto than on bodies with higher mean impact velocity. The low impact velocities and correspondingly low volumes of impact melt generated at Pluto might prevent the occurrence, or limit the size, of floor-pits if their formation involves impact melt water. The presence, or not, of central floor-pit craters on Pluto will thus provide a valuable test of floor-pit formation theories. The presence of summit-pits or concentric craters on Pluto is plausible and would indicate the presence of layering in the near sub-surface. Palimpsests, multi-ring basins and other crater morphologies associated with high heat flow are not expected and would have important implications for Pluto’s thermal history if observed by New Horizons.
• Bray, V. J., Chojnacki, M., Ding, N., Mattson, S. S., Mcewen, A. S., Okubo, C. H., & Tornabene, L. L. (2015). The central uplift of Ritchey crater, Mars. Icarus, 252, 255-270. doi:10.1016/j.icarus.2014.11.001
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  Abstract Ritchey crater is a ∼79 km diameter complex crater near the boundary between Hesperian ridged plains and Noachian highland terrain on Mars (28.8°S, 309.0°E) that formed after the Noachian. High Resolution Imaging Science Experiment (HiRISE) images of the central peak reveal fractured massive bedrock and megabreccia with large clasts. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral analysis reveals low calcium pyroxene (LCP), olivine (OL), hydrated silicates (phyllosilicates) and a possible identification of plagioclase bedrock. We mapped the Ritchey crater central uplift into ten units, with 4 main groups from oldest and originally deepest to youngest: (1) megabreccia with large clasts rich in LCP and OL, and with alteration to phyllosilicates; (2) massive bedrock with bright and dark regions rich in LCP or OL, respectively; (3) LCP and OL-rich impactites draped over the central uplift; and (4) aeolian deposits. We interpret the primitive martian crust as igneous rocks rich in LCP, OL, and probably plagioclase, as previously observed in eastern Valles Marineris. We do not observe high-calcium pyroxene (HCP) rich bedrock as seen in Argyre or western Valles Marineris. The association of phyllosilicates with deep megabreccia could be from impact-induced alteration, either as a result of the Richey impact, or alteration of pre-existing impactites from Argyre basin and other large impacts that preceded the Ritchey impact, or both.
• Moore, J. M., Howard, A. D., Schenk, P. M., Mckinnon, W. B., Pappalardo, R. T., Ewing, R. C., Bierhaus, E. B., Bray, V. J., Spencer, J. R., Binzel, R. P., Grundy, W. M., Olkin, C. B., Reitsema, H. J., Reuter, D. C., Stern, S. A., Young, L. A., Beyer, R. A., Buratti, B. J., & Weaver, H. A. (2015). Geology before Pluto: Pre-encounter considerations. Icarus, 246, 65-81. doi:10.1016/j.icarus.2014.04.028
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  The cameras of New Horizons will provide robust data sets that should be imminently amenable to geological analysis of the Pluto system’s landscapes. In this paper, we begin with a brief discussion of the planned observations by the New Horizons cameras that will bear most directly on geological interpretability. Then we broadly review the major geological processes that could potentially operate on the surfaces of Pluto and its major moon Charon. We first survey exogenic processes (i.e. those for which energy for surface modification is supplied externally to the planetary surface): impact cratering, sedimentary processes (including volatile migration), and the work of wind. We conclude with an assessment of the prospects for endogenic activity in the form of tectonics and cryovolcanism.
• Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., Mckinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Bauman, J., Barnouin, O. S., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Bogan, D. J., Bray, V. J., Brozovic, M., , Buckley, M. R., et al. (2015). The Pluto system: Initial results from its exploration by New Horizons.. Science (New York, N.Y.), 350(6258), aad1815. doi:10.1126/science.aad1815
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  The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.
• Bray, V. J., Collins, G. S., Morgan, J. V., Melosh, H. J., & Schenk, P. M. (2014). Hydrocode simulation of Ganymede and Europa cratering trends – How thick is Europa’s crust?. Icarus, 231, 394-406. doi:10.1016/j.icarus.2013.12.009
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  Abstract One of the continuing debates of outer Solar System research centers on the thickness of Europa’s ice crust, as it affects both the habitability and accessibility of its sub-surface ocean. Here we use hydrocode modeling of the impact process in layered ice and water targets and comparison to Europan cratering trends and Galileo-derived topographic profiles to investigate the crustal thickness. Full or partial penetration of the ice crust by an impactor occurred in simulations in which the ice thickness was less than 14 times the projectile radius. Craters produced in these thin-shell simulations were consistently smaller than for larger ice thicknesses, which will complicate inference of large impactor population sizes. Simulations in which the resultant crater was 3 times the ice layer thickness resulted in summit-pit morphology. This work supports that summit pit craters noted on both rocky and icy bodies, can be created by the presence of a weaker layer at depth. We suggest that floor pits, seen only on ice-rich bodies, require a different formation mechanism to summit pits. Pristine craters formed in a target with high heat flow were shallower than for the same impact into a target of lesser heat flow, suggesting that the ‘starting’ crater morphology for viscous relaxation, isostatic readjustments and erosion rate studies is different for craters formed in times of different heat flow. We find that the crater depth–diameter trend of Europa can only be recreated when simulating impact into an upper brittle ice layer of 7 km depth, with a corresponding geothermal gradient of 0.025 K/m. As this ice thickness estimate is below ∼10 km, results from this work suggest that convective overturn of the surface ice may occur, or have occurred, on Europa making the development of indigenous life a possibility.
• Neish, C. D., Madden, J., Carter, L. M., Hawke, B. R., Bray, V. J., Osinski, G. R., Cahill, J. T., & Giguere, T. A. (2014). Global Distribution of Lunar Impact Melt Flows. Icarus, 239, 105-117. doi:10.1016/j.icarus.2014.05.049
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  Abstract In this study, we analyzed the distribution and properties of 146 craters with impact melt deposits exterior to their rims. Many of these craters were only recently discovered due to their unusual radar properties in the near-global Mini-RF data set. We find that most craters with exterior deposits of impact melt are small, ⩽20 km, and that the smallest craters have the longest melt flows relative to their size. In addition, exterior deposits of impact melt are more common in the highlands than the mare. This may be the result of differing target properties in the highlands and mare, the difference in titanium content, or the greater variation of topography in the highlands. We find that 80% of complex craters and 60% of simple craters have melt directions that are coincident or nearly coincident with the lowest point in their rim, implying that pre-existing topography plays a dominant role in melt emplacement. This is likely due to movement during crater modification (complex craters) or breached crater rims (simple craters). We also find that impact melt flows have very high circular polarization ratios compared to other features on the Moon. This suggests that their surfaces are some of the roughest material on the Moon at the centimeter to decimeter scale, even though they appear smooth at the meter scale.
• Neish, C. D., Kirk, R. L., Lorenz, R. D., Bray, V. J., Stiles, B. W., Hayes, A., Mitchell, K. F., Schenk, P. M., & Turtle, E. P. (2013). Crater Topography on Titan: Implications for Landscape Evolution. Icarus, 223(1), 82-90. doi:10.1016/j.icarus.2012.11.030
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  Abstract We present a comprehensive review of available crater topography measurements for Saturn’s moon Titan. In general, the depths of Titan’s craters are within the range of depths observed for similarly sized fresh craters on Ganymede, but several hundreds of meters shallower than Ganymede’s average depth vs. diameter trend. Depth-to-diameter ratios are between 0.0012 ± 0.0003 (for the largest crater studied, Menrva, D ∼ 425 km) and 0.017 ± 0.004 (for the smallest crater studied, Ksa, D ∼ 39 km). When we evaluate the Anderson–Darling goodness-of-fit parameter, we find that there is less than a 10% probability that Titan’s craters have a current depth distribution that is consistent with the depth distribution of fresh craters on Ganymede. There is, however, a much higher probability that the relative depths are uniformly distributed between 0 (fresh) and 1 (completely infilled). This distribution is consistent with an infilling process that is relatively constant with time, such as aeolian deposition. Assuming that Ganymede represents a close ‘airless’ analogue to Titan, the difference in depths represents the first quantitative measure of the amount of modification that has shaped Titan’s surface, the only body in the outer Solar System with extensive surface–atmosphere exchange.
• Bray, V. J., Atwood-stone, C., & Mcewen, A. M. (2012). Investigating the transition from central peak to peak‐ring basins using central feature volume measurements from the Global Lunar DTM 100 m. Geophysical Research Letters, 39(21), n/a-n/a. doi:10.1029/2012gl053693
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  [1] Several theories have been suggested to explain the transition from peak to peak-ring crater morphology. In order to explore the transition and assess the currently advocated peak-ring formation theories, we have collected measurements of central feature volumes and heights for relatively fresh lunar impact craters. We employed the Global Lunar DTM 100 m, which has the vertical precision and spatial coverage necessary to accurately measure peak and peak-ring volumes in more craters than previously possible. The similarity in both trend and magnitude of peak and peak-ring volumes suggests that peak-ring formation is closely related to the development of central peaks as crater size increases. Our data thus lends support to those peak-ring formation theories involving peak collapse.
• Bray, V. J., Boyce, J. M., Caudill, C. M., Grant, J. A., Hamilton, C. W., Mattson, S., Mcewen, A. S., Mouginis-mark, P. J., Osinski, G. R., & Tornabene, L. L. (2012). Widespread crater-related pitted materials on Mars: Further evidence for the role of target volatiles during the impact process. Icarus, 220(2), 348-368. doi:10.1016/j.icarus.2012.05.022
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  Abstract Recently acquired high-resolution images of martian impact craters provide further evidence for the interaction between subsurface volatiles and the impact cratering process. A densely pitted crater-related unit has been identified in images of 204 craters from the Mars Reconnaissance Orbiter. This sample of craters are nearly equally distributed between the two hemispheres, spanning from 53°S to 62°N latitude. They range in diameter from ∼1 to 150 km, and are found at elevations between −5.5 to +5.2 km relative to the martian datum. The pits are polygonal to quasi-circular depressions that often occur in dense clusters and range in size from ∼10 m to as large as 3 km. Pit sizes scale with both the host crater’s diameter and the host deposit size. These pits have subtle raised rims, and unlike primary and secondary impact craters, they lack well-defined ejecta deposits and overlapping stratigraphic relationships. They also lack any sign of any preferential alignment expected of volcanic or tectonic collapse features. Morphologic and stratigraphic evidence in support of an impact origin includes the observation that pitted materials primarily occur as ponded and flow-like deposits on crater floors, behind terraces, and infilling the lowest local topographic depressions atop the ejecta blanket—similar to the distribution of impact melt-bearing bodies on the Moon. Based on the observations and comparisons to terrestrial and lunar analogs, we conclude that the pit-bearing materials are impactite deposits. The presence of these deposits in older craters, where preserved, suggests that they have formed on Mars throughout most of its geologic history; thus, understanding their origin may help to constrain the hydrological and climate history of Mars.
• Bray, V. J., Schenk, P. M., Morgan, J. V., Collins, G. S., & Melosh, H. J. (2012). Ganymede crater dimensions - Implications for central peak and central pit formation and development. Icarus, 217(1), 115-129. doi:10.1016/j.icarus.2011.10.004
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  The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. The differences are thought due to the relative weakness of ice and the possible presence of sub-surface water layers. Digital elevation models constructed from Galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of Ganymede. Measurements were made from multiple profiles across each crater, so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed. The additional depth, slope and volume information reported in this work has enabled study of central peak formation and development, and allowed a quantitative assessment of the various theories for central pit formation. We note a possible difference in the size-morphology progression between small craters on icy and silicate bodies, where central peaks occur in small craters before there is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely, our crater dimension analyses suggest that the size-morphology progression of large lunar craters from central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequently modified to a central pit morphology. Pit formation may occur via the collapse of surface material into a void left by the gradual release of impact-induced volatiles or the drainage of impact melt into sub-crater fractures.
• Elder, C. M., Bray, V. J., & Melosh, H. J. (2012). The theoretical plausibility of central pit crater formation via melt drainage. Icarus, 221(2), 831-843. doi:10.1016/j.icarus.2012.09.014
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  Central pit craters are seen in large craters on some icy satellites and on Mars. We investigate the hypothesis that central pits form when impact melt drains into fractures beneath the impact crater. For this process to occur, the volume of melt generated during the impact, the volume of void space in fractures beneath the impact crater, and the volume of melt able to drain before the fractures freeze shut all must exceed the volume of the observed central pits. We estimate the volume of melt generated using results from previous numerical modeling studies. The fracture volume is estimated using gravity anomalies over terrestrial craters. To estimate the amount of melt able to drain before freezing, we consider flow through plane parallel fractures. These calculations all suggest that enough liquid water could drain into fractured ice beneath a crater on Ganymede to form a central pit. On Earth and the Moon, silicate impact melt will freeze before a large volume is able to drain, so we do not expect to see central pits in impact craters in targets with no ice. In summary, we find our calculations are consistent with observed central pits in craters on Ganymede and the lack of central pits in craters on Earth and the Moon.
• Bray, V. J., Dundas, C. M., Keszthelyi, L. P., & Mcewen, A. S. (2010). Role of material properties in the cratering record of young platy‐ridged lava on Mars. Geophysical Research Letters, 37(12), 1-5. doi:10.1029/2010gl042869
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  [1] Platy-ridged surfaces in the Elysium Planitia region of Mars exhibit different crater densities on rafted plates and polygonally patterned areas between them. Rather than being indicative of different ages, these differences provide insight into the variable strength of different types of lava surface. The sizes of small craters, and the resulting size-frequency distribution (SFD), depend on the material strength of target surfaces. Brecciated lava surfaces are likely to have higher crater densities than coherent lava.
• Bray, V. J., Keszthelyi, L. P., Caudill, C. M., Bogert, C. H., Caudill, C. M., Gaddis, L. R., Garry, W. B., Giguere, T. A., Hawke, B. R., Kattenhorn, S. A., Keszthelyi, L. P., Mcewen, A. S., Rizk, B., & Tornabene, L. L. (2010). New insight into lunar impact melt mobility from the LRO camera. Geophysical Research Letters, 37(21), n/a-n/a. doi:10.1029/2010gl044666
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  [1] The Lunar Reconnaissance Orbiter Camera (LROC) is systematically imaging impact melt deposits in and around lunar craters at meter and sub-meter scales. These images reveal that lunar impact melts, although morphologically similar to terrestrial lava flows of similar size, exhibit distinctive features (e.g., erosional channels). Although generated in a single rapid event, the post-impact mobility and morphology of lunar impact melts is surprisingly complex. We present evidence for multi-stage influx of impact melt into flow lobes and crater floor ponds. Our volume and cooling time estimates for the post-emplacement melt movements noted in LROC images suggest that new flows can emerge from melt ponds an extended time period after the impact event.
• Byrne, S., Bray, V. J., Banks, M. E., Dundas, C. M., Fishbaugh, K. E., Galla, K., Herkenhoff, K. E., Mcewen, A. S., & Murray, B. C. (2010). Crater population and resurfacing of the Martian north polar layered deposits. Journal of Geophysical Research, 115(8). doi:10.1029/2009je003523
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  Present-day accumulation in the north polar layered deposits (NPLD) is thought to occur via deposition on the north polar residual cap. Understanding current mass balance in relation to current climate would provide insight into the climatic record of the NPLD. To constrain processes and rates of NPLD resurfacing, a search for craters was conducted using images from the Mars Reconnaissance Orbiter Context Camera. One hundred thirty craters have been identified on the NPLD, 95 of which are located within a region defined to represent recent accumulation. High Resolution Imaging Science Experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal. A classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth/diameter ratios were determined. The temporal and spatial distribution of crater degradation is interpreted to be close to uniform. Through comparison of the size-frequency distribution of these craters with the expected production function, the craters are interpreted to be an equilibrium population with a crater of diameter D meters having a lifetime of ~30.75D^(1.14) years. Accumulation rates within these craters are estimated at 7.2D^(−0.14) mm/yr, which corresponds to values of ~3–4 mm/yr and are much higher than rates thought to apply to the surrounding flat terrain. The current crater population is estimated to have accumulated in the last ~20 kyr or less.
• Reufer, A., Thomas, N., Benz, W., Byrne, S., Bray, V. J., Dundas, C. M., & Searls, M. L. (2010). Models of high velocity impacts into dust-covered ice: Application to Martian northern lowlands. Planetary and Space Science, 58(10), 1160-1168. doi:10.1016/j.pss.2010.04.008
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  The detection of fresh impact craters with bright floors and ejecta (arising from fresh clean water ice) in the northern lowlands of Mars (Byrne et al., 2009b, Science 325, 1674), together with observations of polygonal structures and evidence from the Phoenix probe, suggests that there are substantial water ice deposits just below the surface over large areas. Specifically in cases of the larger craters observed, the impacts themselves may have raised the temperature and the pressure of the water ice deposits locally to values which allow phase changes. In this paper, we use smoothed particle hydrodynamics to model hyper-velocity impacts. We estimate peak shock pressures in a solid water ice target covered by a layer of loose material, modeled by pre-damaged dunite. In addition, we account for the possibility of a thin layer of sub-surface water ice by using a three-layer model where the ice is surrounded by dunite. We find that the peak shock pressures reached in the simulated events are high enough to produce several 100–1000 kg of liquid water depending upon the impact parameters and the exact shock pressure needed for the phase change. A difficulty remains however in determining whether liquid is generated or whether a type of fluidized ice is produced (or indeed some combination of the two). We also note that the process can become rather complex as the number of layers increases because of reflections of the shock at sub-surface boundaries—a process which should lead to increased fluidization.
• Bray, V. J., Collins, G. S., Morgan, J. V., & Schenk, P. M. (2008). The effect of target properties on crater morphology: Comparison of central peak craters on the Moon and Ganymede. Meteoritics & Planetary Science, 43(12), 1979-1992. doi:10.1111/j.1945-5100.2008.tb00656.x
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  We examine the morphology of central peak craters on the Moon and Ganymede in order to investigate differences in the near-surface properties of these bodies. We have extracted topographic profiles across craters on Ganymede using Galileo images, and use these data to compile scaling trends. Comparisons between lunar and Ganymede craters show that crater depth, wall slope and amount of central uplift are all affected by material properties. We observe no major differences between similar-sized craters in the dark and bright terrain of Ganymede, suggesting that dark terrain does not contain enough silicate material to significantly increase the strength of the surface ice. Below crater diameters of ?12 km, central peak craters on Ganymede and simple craters on the Moon have similar rim heights, indicating comparable amounts of rim collapse. This suggests that the formation of central peaks at smaller crater diameters on Ganymede than the Moon is dominated by enhanced central floor uplift rather than rim collapse. Crater wall slope trends are similar on the Moon and Ganymede, indicating that there is a similar trend in material weakening with increasing crater size, and possibly that the mechanism of weakening during impact is analogous in icy and rocky targets. We have run a suite of numerical models to simulate the formation of central peak craters on Ganymede and the Moon. Our modeling shows that the same styles of strength model can be applied to ice and rock, and that the strength model parameters do not differ significantly between materials.

Proceedings Publications

• Bray, V., Nicholson, U., & Gulick, S. (2024, apr). The Importance of Drill Cores for Impact Cratering and Astrobiology Studies. In Integrating Ocean Drilling and NASA Science: A Workshop to Explore Missions to Planet Earth, 3013.
• Bray, V., Nicholson, U., Gulick, S., Collins, G., Powell, W., Kenkmann, T., & Duarte, D. (2024, mar). A Seismic Treasure Trove: 3D Anatomy of the Nadir Marine-Target Impact Crater. In 55th Lunar and Planetary Science Conference, 3040.
• Dundas, C., Daubar, I., McEwen, A., & Bray, V. (2024, mar). Controls on the Formation of Secondary Markings Around New Impacts on Mars. In 55th Lunar and Planetary Science Conference, 3040.
• Sandtorf-McDonald, J., Bray, V., & Chevrier, V. (2024, mar). Titan Craters in Ice Targets: Comparing Updated Ice Strength with Previous Values. In 55th Lunar and Planetary Science Conference, 3040.
• Sandtorf-McDonald, J., Bray, V., Craft, K., & Rhoden, A. (2024, mar). Comparing Europa Crater Results with Updated Ice Hardness in iSALE. In 55th Lunar and Planetary Science Conference, 3040.
• Schmerr, N., Benna, M., McCall, N., Marusiak, A., Bailey, S., DellaGiustina, D., Bray, V., Byrne, P., Avenson, B., Kim, D., & Shah, N. (2024, jul). The Lunar Environmental Monitoring Station: An Artemis 3 Deployed Instrument. In Mars Interior and Geophysics After InSight, 3060.
• Bland, M., & Bray, V. (2023, mar). Large Shallow Craters on Callisto and Ganymede as an Inevitable Result of Viscous Relaxation. In LPI Contributions, 2806.
• Bray, V., Zeilnhofer, M., Schenk, P., Bland, M., & Robbins, S. (2023, mar). Complex Impact Crater Dimensions on Large Icy Bodies. In LPI Contributions, 2806.
• Avenson, B., Bailey, S. H., Bray, V. J., Dahl, P. H., Della-giustina, D. N., Dellagiustina, D., Durfey, V. J., Marusiak, A. G., Pettit, E. C., Schmerr, N., Wagner, N., & Weber, R. C. (2020). Cluster Analysis of Thermal Icequakes Using the Seismometer to Investigate Ice and Ocean Structure (SIIOS): Implications for Ocean World Seismology. In LPSC.
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  Introduction: Ocean Worlds are of high interest to the planetary community [1, 2] due to the potential habitability of their subsurface oceans [3–5]. Over the next few decades several missions will...
• Daubar, I., Dundas, C. M., Bray, V. J., Tornabene, L. L., Bart, G. D., & Speyerer, E. J. (2019). THE THRILLING IMPACT OF CRATERS IN HIGH RESOLUTION. In GSA.
• Dellagiustina, D., Bailey, S. H., Avenson, B., Weber, R. C., Schmerr, N., Wagner, N., Bray, V. J., Della-giustina, D. N., Durfey, V. J., Marusiak, A. G., & Pettit, E. C. (2019). Ambient Seismicity on Europan Analogs using the Seismometer to Investigate Ice and Ocean Structure (SIIOS). In NASA instrument development update.
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  The Seismometer to Investigate Ice and Ocean Structure (SIIOS) project is exploring the science capabilities of seismometers in ocean world analog environments. Ocean worlds, such as Europa, Encela...
• Smith, D. E., Zuber, M. T., Canup, R. M., Hurford, T., Bierhaus, B., Bland, M. T., Connerney, J. E., Genova, A., Johnson, C. L., Khurana, K., Lunine, J. I., Mazarico, E., Neumann, G. A., Nimmo, F., Pappalardo, R. T., Paty, C. S., Wieczorek, M. A., Durfey, V. J., Prockter, L. M., & Rhoden, A. R. (2019). MAGIC, A Discovery Proposal to the Icy Moon Callisto. In Discovery Proposal.
• Robbins, S. J., Beyer, R. A., Spencer, J. R., White, O. L., Singer, K. N., Ore, C. M., Mckinnon, W. B., Lisse, C. M., Runyon, K. D., Beddingfield, C. B., Schenk, P. M., Cruikshank, D. P., Lauer, T. R., Bray, V. J., Binzel, R. P., Buie, M. W., Buratti, B. J., Cheng, A. C., Linscott, I. R., , Reuter, D. C., et al. (2018). Geologic Map of New Horizons' Encounter Hemisphere of Charon, III. In GSA.
• Grundy, W. M., Berry, K. L., Beyer, R. A., Binzel, R. P., Bray, V. J., Buie, M. W., Buratti, B. J., Cheng, A. C., Cook, J. C., Cruikshank, D. P., Ore, C. M., Earle, A. M., Ennico, K., Jennings, D. E., Howett, C. J., Kaiser, R. I., Lauer, T. R., Linscott, I. R., Lisse, C. M., , Lunsford, A. W., et al. (2016). WHAT HAVE WE LEARNED ABOUT CHARON FROM NEW HORIZONS. In GSA.
• Mckinnon, W. B., Schenk, P. M., Moore, J. M., Howard, A. D., Nimmo, F., Singer, K. N., Bray, V. J., Young, L. A., Olkin, C., Ennico, K., Weaver, H. A., & Stern, S. A. (2016). AN IMPACT BASIN ORIGIN FOR SPUTNIK “PLANITIA” AND SURROUNDING TERRAINS, PLUTO. In GSA.
• Singer, K. N., Mckinnon, W. B., Greenstreet, S., Gladman, B., Parker, A., Robbins, S. J., Schenk, P. M., Spencer, J. R., Stern, S. A., Bray, V. J., Weaver, H. A., Howard, A. D., Young, L. A., Ennico, K., Binzel, R. P., Moore, J. M., Olkin, C. B., & Team, N. H. (2016). PLUTO SYSTEM CRATERING HISTORY AND SURFACE AGES. In GSA.
• Robbins, S. J., Singer, K. N., Schenk, P. M., Zangari, A. M., Mckinnon, W. B., Runyon, K. D., Beyer, R. A., Porter, S. B., Lauer, T. R., Olkin, C., Smith, K. E., Stern, A., Durfey, V. J., Weaver, H. A., & Young, L. A. (2015). Crater Mapping in the Pluto-Charon System: Considerations, Approach, and Progress. In AGU.