The contamination of the surface of Vesta by impacts and the delivery of the dark material

The Dawn spacecraft observed the presence of dark material, which in turn proved to be associated with OH and H-rich material, on the surface of Vesta. The source of this dark material has been identified with the low albedo asteroids, but it is still a matter of debate whether the delivery of the dark material is associated with a few large impact events, to micrometeorites or to the continuous, secular flux of impactors on Vesta. The continuous flux scenario predicts that a significant fraction of the exogenous material accreted by Vesta should be due to non-dark impactors likely analogous to ordinary chondrites, which instead represent only a minor contaminant in the HED meteorites. We explored the continuous flux scenario and its implications for the composition of the vestan regolith, taking advantage of the data from the Dawn mission and the HED meteorites. We used our model to show that the stochastic events scenario and the micrometeoritic flux scenario are natural consequences of the continuous flux scenario. We then used the model to estimate the amounts of dark and hydroxylate materials delivered on Vesta since the LHB and we showed how our results match well with the values estimated by the Dawn mission. We used our model to assess the amount of Fe and siderophile elements that the continuous flux of impactors would mix in the vestan regolith: concerning the siderophile elements, we focused our attention on the role of Ni. The results are in agreement with the data available on the Fe and Ni content of the HED meteorites and can be used as a reference frame in future studies of the data from the Dawn mission and of the HED meteorites. Our model cannot yet provide an answer to the fate of the missing non-carbonaceous contaminants, but we discuss possible reasons for this discrepancy.Comment: 31 pages, 7 figures, 4 tables. Accepted for publication on the journal ICARUS, "Dark and Bright Materials on Vesta" special issu

Second International Colloquium on Mars: Abstracts for a colloquium

Abstracts of 110 papers relating to investigations of the planet Mars and intended for consideration at the colloquium are presented. Entries are arranged alphabetically according to the author's name

Icy Satellite Tectonic, Geodynamic and Mass Wasting Surface Features: Constraints on Interior Processes and Evolution

Empirical data collected from mapping campaigns combined with modeling of geologic processes improves our understanding of planetary geology. Many planet- or satellite-scale processes cannot be reproduced in labs, thus analyzing surface features provides insights to confirm, discount, or improve models. I present the methods used to map and characterize the morphometry of several types of geologic features found on three icy satellites of Jupiter and Saturn, and the resulting data. Trends in the data provide insight into feature formation, and to both surface and interior processes occurring in icy satellites. Topics include: i) linear features and despinning stresses on Iapetus, ii) long-runout landslides and friction reduction on Iapetus, iii) pits, uplifts, and small chaos regions on Europa and what they reveal about ice shell thickness, iv) relaxed impact craters and the thermal history of Ganymede, and v) the size-velocity distribution of ejecta fragments from large cratering events on Europa and Ganymede

Enceladus and the Icy Moons of Saturn : July 26-29, 2016, Boulder, Colorado

Topics include (but are not limited to) geology, geophysics, geochemistry and mineralogy, active jets and their properties and origins, formation and evolution, astrobiology, and future investigations of these bodies. Comparative planetology is encouraged. A major focus will be the new results from the 2015 Cassini encounters with Enceladus and the other icy moons. Contributions from Cassini, Voyager, and groundbased studies are welcomeUniversities Space Research Association (USRA), Lunar and Planetary Institute (LPI)Local Organizing Committee, Larry Esposito, University of Colorado Carly Howett, Southwest Research Institute Laura Bloom, University of Colorado ; Science Organizing Committee Paul Schenk, Lunar and Planetary Institute [and 12 others

Bridging the Gap II, effect of target properties on the impact cratering process: September 22-26, 2007, Saint-Hubert, Canada

The purpose of this workshop is to bring together researchers from various disciplines to address one of its major outstanding problems: the effect of target properties, such as porosity, volatiles, and layering, on the impact cratering process.Canadian Space Agencysponsors, Canadian Space Agency ... [and others] ; conveners, Robert Herrick, Gordon Osinski, Elizabetta Pierazzo ; scientific organizing committee, Mark Burchell ... [and others]

Large-scale volcanism on the terrestrial planets

Evidence for mafic volcanism has been found on each planet in the inner Solar System. Lava flows on these planets range in size from 10s to 1000s of kilometers in extent. I investigated large-scale lava flows on Mercury, Earth, and Mars throughout the chapters in this dissertation. Each of these lava flows provides an avenue to study the emplacement and evolution of lava on various planets and under differing conditions, the factors that affect their overall extent, and potential source areas. Chapter One investigates large-scale lava flows in the Cerberus region on Mars, specifically to understand their emplacement history, material properties, and possible magma sources. Mapping and crater counting are used to investigate these flows. The derived absolute age estimates suggest an anomalous trend of decreasing ages with increasing distance from the flow source. Through pi-group scaling, changes to the material properties of the lavas during emplacement are identified as the cause for this decreasing age trend and are attributed to increased strength, and decreased porosity, of the lava. These newly derived absolute age estimates are also used to infer the source of the magma feeding these young and extensive lava flows originated below the Cerberus region. Chapter Two focuses on long and areally extensive lava flows on Earth and Mars, in order to determine the effect of viscosity on the emplacement of 1000+ km flows. In particular, low viscosity lavas are expected to generate such large lava flows. The terrestrial and martian lava flows are interpreted to have been emplaced rapidly, with their final extents limited by the total erupted volume of lava. Through computer modeling, simulations are performed to determine the viscosity values responsible for the observed lava flow extents. The results of this work support low bulk viscosities that correspond to a basaltic composition produce the best reproductions of the martian flows. Chapter Three investigates volcanism on Mercury, which hosts broad smooth plains in three locales, which have varying interpretations for their emplacement, though volcanic processes are favored. The smooth plains units located in the annulus surrounding the Caloris impact basin contain intermingled high-reflectance red and low-reflectance blue plains. Mapping, crater counting, and spectral analyses are used to suggest the emplacement mechanism for these smooth plains. The results of this work support a volcanic origin, though impact related processes cannot be discounted

Simulation of Europa's water plume and structures related to energetic activities on solar system bodies from satellite images

This PhD thesis focuses on the analysis of different high energetic processes that affect the surface of planets, satellites and minor bodies as well as modify their surrounding environment. Specifically, this work concerns three main topics: (i) the simulation and analysis of one of the most geological energetic process, i.e. impact cratering; (ii) the investigation of the fragmentation processes that could have generated boulders on comet Churyumov-Gerasimenko 67P; (iii) the analysis of a possible transient plume originating from cryovolcanic events on Europa, the Jovian icy satellite, combined with an accurate characterisation of its exospheric background. The first topic addresses the investigation of the impact formation process through numerical modelling. Shocks code represent the most feasible method for studying impact craters, as they can simulate a large span of conditions beyond the reach of experiments (e.g., velocity, size). The iSALE hydrocode was used to simulate two different impact structures located on Mercury and Mars. On Mercury, the simulation allows to determine the genesis of a particular landform, i.e. a steep-sided cone with associated pyroclastic deposits, which was revealed by images acquired by MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. On Mars, the simulation of the Firsoff crater in Arabia Terra permits a better understanding the subsequent geologic processes that led to crater post modification, defining which rheological structure is more likely in that region. In both cases, we conclude that the numerical modelling of impact process is a powerful tool to improve the comprehension of the Solar System. The second topic of the thesis has been developed after the Rosetta mission got inserted around the comet Churyumov-Gerasimenko 67P. We investigated the surface of comet Churyumov-Gerasimenko 67P focusing on the possible energetic events that lead to the formation of boulders; i.e. blocks that are ubiquitous on the surface of the comet. Different energetic formation processes were invoked to explain the presence of boulders, such as sublimation, fragmentation, outbursts and gravitational falls. Using images acquired by OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) and CIVA (Comet Infrared and Visible Analyser) cameras on board the spacecraft and the lander respectively, a quantitative analysis of different-size boulders has been performed in order to understand if the same energetic formation processes occur equally on different scales on the comet (m, cm and mm). Specifically, by means of different resolution images, we obtained several size-frequency distribution for: (i) boulders larger than 7 m, (ii) boulders larger than 1 m from higher resolution images used to analyse the Abydos site, the location where Philae is supposed to be, and (iii) pebbles (mm-scale structures) visible on CIVA images. The third topic is the icy satellite Europa in view of the future ESA/JUICE mission and because of our involvement in JANUS (Jovis, Amorum ac Natorum Undique Scrutator) visible camera. The presence of a subsurface ocean is a primary topic on Europa, in addition the recent discovery of a transient plume at the south pole by HST observations has raised many questions regarding the interaction between the subsurface/surface and the outer environment of Europa in terms of active processes affecting the icy surface. In this context, a possible plume deposit originating from cryovolcanic events was simulated to understand its detectability by JANUS camera during the Europa flyby phase of the JUICE mission. In addition, since the study of transient plumes has as a mandatory prerequisite an accurate characterisation of the exospheric background, a detailed study of the loss rates of Europa's tenuous atmosphere was performed. In particular, loss rates for electron impact dissociation and ionization processes, for charge-exchange (considering plasma torus, pick up and ionosphere ions) and for photo processes (for both cases of quite and active Sun) were calculated