Icy Surfaces Research Articles

Framework of simulation-based vehicle safety performance assessment of highway system under hazardous driving conditions

Vehicles are extremely vulnerable to single-vehicle accidents under some hazardous driving conditions (i.e. strong wind, icy or snowy road surface). An integrated framework is proposed to assess single-vehicle traffic safety performance of stochastic traffic flow under hazardous driving conditions. Different from most existing studies focusing on a single vehicle moving at a constant speed, for the first time, the proposed work evaluates individual vehicle safety performance based on the time-dependent simulation results of stochastic traffic flow, including instantaneous speeds and positions of each vehicle as a part of simulated traffic flow. Simultaneously, complex geometric and other environmental conditions of the highway system are also considered realistically, not only during the safety assessment process, but also in quantifying the wind loads applied on the vehicles. Finally, with the safety information of each individual vehicle, an overall safety performance index of the whole traffic flow on the highway system is further introduced, which serves as a potential traffic safety performance measure and resilience indicator of transportation infrastructure systems under various hazards. This study has potential applications to not only regular vehicles, but also advanced traffic management and control algorithms for connected and autonomous vehicles in hazardous driving environments.

Louder Than Films: Memory, Affect and the ‘Sublime Image’ in the Work of Joachim Trier

“We have to believe that new images are still possible”. This remark by Norwegian filmmaker Joachim Trier during a recent event in Oslo entitled ‘The Sublime Image’ speaks to the centrality in his work of images, often of trauma, that aspire to the condition of photographic stills or paintings. A hand against a window, cheerleaders tumbling against an azure sky, an infant trapped under a lake’s icy surface: these can certainly be read as sublime images insofar as we might read the sublime as an affect—a sense of the ineffable or the shock of the new. However, for Trier, cinema is an art of memory and here too, this article argues, his films stage an encounter with the temporal sublime and the undecidability of memory. Offering readings of Trier’s four feature films to date which center on their refraction of memory through crystal-images, the article emphasizes the affective encounter with the films as having its own temporality.

Using cosmogenic Lithium, Beryllium and Boron to determine the surface ages of icy objects in the outer solar system

Given current uncertainties in the cratering rates and geological histories of icy objects in the outer solar system, it is worth considering how the ages of icy surfaces could be constrained with measurements from future landed missions. A promising approach would be to determine cosmic-ray exposure ages of surface deposits by measuring the amounts of cosmogenic Lithium, Beryllium and Boron at various depths within a few meters of the surface. Preliminary calculations show that ice that has been exposed to cosmic radiation for one billion years should contain these cosmogenic nuclei at concentrations of a few parts per trillion, so any future experiment that might attempt to perform this sort of measurement will need to meet stringent sensitivity requirements.

Safety aspects on icy asphalt pavement in cold region through field investigations

It has been proved that ice shows different friction regimes. This work focuses on rubber friction on ice, a topic of great practical significance when it comes to grip of tires on icy road surfaces. Here the possibility of using Dynamic Friction Tester (DFT) for assessing skid resistance under icy condition is presented. The ice thickness was then controlled by the volume of the freezing water spraying on a consistent area so that the surfaces were characterized by different degrees of ice coverage. As a consequence, eight surface conditions were considered and tests were conducted at different temperatures ranging from −5 to −20 °C. In addition, aiming at the analysis of the changes due to wear of ice, several cycles of measurements were conducted and the effect of the temperature was investigated. The results showed that the dynamic friction coefficient reached steady state on icy surfaces during decelerating process, which is much lower than other conditions. Moreover, the data reached a low point at −14 °C, resulting from the thermal equilibrium between the dissipation of frictional heat during the contact and the melting of the ice layer between two consecutive passages.

Slip resistance and wearability of safety footwear used on icy surfaces for outdoor municipal workers.

BACKGROUND:Outdoor workers experience high injury rates in the winter due to slipping on ice and snow. Our testing program has demonstrated that most safety footwear does not provide adequate slip-resistance and/or comfort in icy conditions.OBJECTIVE:Our objective was to determine which of the most commonly worn safety footwear available to outdoor municipal workers in Toronto, Ontario, Canada would best prevent slips on icy surfaces and which models had good wearability.METHODS:We selected 45 of the most popular types of winter footwear worn by these workers and applied our Maximum Achievable Angle (MAA) test method to rate the slip-resistance of the footwear. A ten-point rating scale was used for recording participants’ perceptions of wearability. The MAA test measured the steepest ice-covered incline that participants can walk up and down without experiencing a slip.RESULTS:Of the 45 types of footwear tested, only one model achieved an MAA score of 8 degrees that exceeded our cut-off for acceptable performance set at 7 degrees. Secondary measures of performance including thermal insulation; wearability and heaviness of footwear tested were also ranked.CONCLUSION:Our results demonstrate that footwear manufactures have the opportunity to differentiate their footwear by investing in slip-resistant outsole materials.

Survival of Radioresistant Bacteria on Europa’s Surface after Pulse Ejection of Subsurface Ocean Water

We briefly present preliminary results of our study of the radioresistant bacteria in a low temperature and pressure and high-radiation environment and hypothesize the ability of microorganisms to survive extraterrestrial high-radiation environments, such as the icy surface of Jupiter’s moon, Europa. In this study, samples containing a strain of Deinococcus radiodurans VKM B-1422T embedded into a simulated version of Europa’s ice were put under extreme environmental (−130 °C, 0.01 mbar) and radiation conditions using a specially designed experimental vacuum chamber. The samples were irradiated with 5, 10, 50, and 100 kGy doses and subsequently studied for residual viable cells. We estimate the limit of the accumulated dose that viable cells in those conditions could withstand at 50 kGy. Combining our numerical modelling of the accumulated dose in ice with observations of water eruption events on Europa, we hypothesize that in the case of such events, it is possible that putative extraterrestrial organisms might retain viability in a dormant state for up to 10,000 years, and could be sampled and studied by future probe missions.

Meet IceWorm: NASA’s New Ice-Climbing Robot

A robot that can inch up icy surfaces may help scientists reach new heights in some of Earth’s most dangerous and remote landscapes.

Combined IR and XPS characterization of organic refractory residues obtained by ion irradiation of simple icy mixtures

Context. Multi-year laboratory experiments have demonstrated that frozen icy mixtures containing simple organic and inorganic molecules (such as H2O, N2, CH4, CO, CO2, C2H6, etc.), if exposed to a flux of energetic ions or UV photons, give rise to new more complex molecules at low temperatures (10–50 K). A fraction of the new synthesized molecules is volatile while the remaining fraction is refractory and therefore it is preserved after the warm-up of the substrate to room temperature. Moreover, a part of the refractory material is formed during the annealing to room temperature, when molecules and radicals into the processed ice become mobile and react to form non-volatile molecules. By means of similar mechanisms, complex organic materials may be formed on the icy surfaces of some objects in the outer solar system, such as trans-Neptunian objects, comets and some satellites of the giant planets: in fact the interaction with solar wind and solar flares ions, solar photons and galactic cosmic rays could produce more refractory materials, analogous to those produced in the laboratory. In some cases, the materials thus synthesized may contain functional groups considered relevant to the pre-biotic chemistry in the hypothesis that interplanetary dust particles, comets and meteoroids contributed to seed the early Earth with the building blocks of life. Aims. The aim of this work is to investigate the chemical similarities and differences between some organic residues left over after ion bombardment (200 keV H+) of different ice mixtures followed by subsequent warm up under vacuum to room temperature. Methods. Seven organic residues have been prepared in our laboratory following a procedure involving the proton irradiation of seven different icy mixtures and their warm-up to room temperature. All the organic samples were characterized by FTIR spectroscopy with measurements performed in situ, in the ultra-high vacuum condition preventing any sample degradation. Three of them were selected to be characterized by XPS spectroscopy as well. Results. Among the organic residues presented in this paper, only those containing nitrogen and carbon exhibit the multi-component band centred at 2200 cm−1. This multi-component band presents interest from the astrobiological point of view due to its attribution to nitriles (–C≡N) and isonitriles (–N≡C). Our results demonstrate that this band is present in the IR spectra of organic nitrogen residues regardless the use of oxygen-bearing species in the icy mixture. This finding is of interest since the 2200 cm−1 band has been observed in some extraterrestrial samples (micro-meteorites) collected in the Antarctica.

Effects of multi-functional surface-texturing on the ice friction and abrasion characteristics of hybrid composite materials for footwear

There is growing demand for composite materials for use with slip-resistant footwear. This paper reports on the optimization of a surface-textured hybrid composite material with good slip-resistance on ice. Our material has a unique design consisting of a soft rubber compound reinforced with a combination of soft and hard microscopic fibers embedded within it that protrude out from its surface. These fibers can penetrate icy surfaces, while the soft rubber component deforms to mold against hard substrates resulting in mechanical interlocking.Our previous work has shown our initial formulations of this composite has superior slip-resistance and abrasion resistance compared to other materials on the market. The objective of this work was to systematically vary manufacturing (fiber content and molding temperature) and testing parameters (normal load and sliding velocity) to evaluate the effects on slip-resistance before and after abrasion.Our hybrid thermoplastic polyurethane (TPU) composites composed of carbon fiber (CF) and poly (p-phenylene-2,6-benzobisoxazole) (PBO) fibers were fabricated by means of compounding followed by ablation. The coefficient of friction on ice was measured before and after simulated wear using SATRA STM 603 slip-resistance testing machine (SATRA). The surface morphology of each composite was also characterized visually using scanning electron microscopy (SEM). The set of experiments used was derived by applying the Taguchi method for robust design.The optimal combination of parameters maximizing the coefficient of friction on ice after abrasion was determined. Before abrasion, the only control factor that affected the ice friction properties of the composite was fiber content (p = 0.024). After abrasion, ice friction was independent of all control factors with no interaction effects and no sensitivity to the testing parameters, indicating the capability of the material to retain its slip-resistance even after extensive wear (COF = 0.61 ± 0.05). The SEM images indicated that there was significant fiber protrusion from the textured surfaces after abrasion. These findings suggest that our hybrid composite material has good potential for use in applications such as winter footwear for providing traction on icy surfaces even after extended use.

Assessing the formation of valley networks on a cold early Mars: Predictions for erosion rates and channel morphology

The ancient Noachian highlands of Mars host an extensive population of valley networks which formed predominantly during the early geologic history of the planet. Morphologic characteristics of the valley networks have been interpreted to indicate the formation of these features through precipitation-derived fluvial activity and therefore as evidence for a relatively warm and wet Noachian Mars climate. However, these interpretations conflict with the results of sophisticated global climate modeling studies, which suggest that early Mars was dominated by a cold and icy climate with conditions characterized by adiabatic cooling and regional ice sheets within the highlands. Difficulties in replicating the warm and wet early climate conditions interpreted from the valley networks has served as the basis for alternative suggestions for the formation of valley networks by transient heating and snowmelt in an otherwise cold and icy climate. Here we test a conceptual model for valley network formation and incision under cold and icy conditions with a substrate characterized by the presence of an ice-free, desiccated surface regolith and subjacent ice-cemented regolith, similar to that found in the Antarctic McMurdo Dry Valleys on Earth. We implement numerical thermal models, quantitative erosion and transport estimates, and morphometric analyses in order to outline and test predictions for: (1) the nature and structure of the cold and icy Noachian substrate, (2) valley network fluvial erosion and incision rates, and (3) resulting channel/valley morphology. Morphologic predictions are compared against observational data to determine if the valley networks characteristics are consistent with formation in a cold and icy climate. Through this approach we present and develop the underlying conceptual model, identify and generate the fundamental data inputs required to evaluate it, and perform a preliminary first-order assessment to serve as a basis for further investigation. While these analyses have been performed over a broad parameter space to address relative uncertainties, we report findings with a specific emphasis on the nominal results.We find that under cold conditions, the substrate is characterized by a kilometers-thick, globally-continuous cryosphere with a ∼ 50–100 m thick ice-free surface layer in diffusive equilibrium with the atmosphere and underlying ice-cemented regolith, the top of which forms the ice-table. Estimates of the potential infiltration capacity of the ice-free surface regolith layer indicate that surface runoff generation does not require excessively large precipitation rates, and thus does not preclude fluvial activity sourced by rainfall. Additionally, due to the predicted thicknesses of the ice-free surface regolith, any transient period of warming would need to be sustained in duration (∼ 2 kyr) to induce melting of ground ice to initiate solifluction/gelifluction activity. The predicted range of ice-table depths is exceeded by the incised depths of a majority of the valley network population, therefore suggesting interactions were possible. Evaluation of the rates of mechanical substrate erosion and thermal ice-cement erosion by valley network fluvial activity are subject to large uncertainties due to several poorly constrained parameters (i.e. the substrate erodibility factor and the valley network fluvial water temperature) but generally indicate that at low water temperatures, consistent with a cold and icy surface environment, thermal erosion of the ice-cement can be outpaced by mechanical erosion of the substrate. In this scenario, the relative efficiency of lateral erosion is predicted to be enhanced during incision below the ice-table, causing preferential channel/valley widening and increased width-to-depth ratios. Assessment of this prediction through a morphometric analysis of valley network width-to-depth ratios and occurrence of U-shaped cross sections indicates no significant correlation to ice-table depths. This result suggests that either: (1) permafrost was not present in the Noachian Mars substrate, indicating a warmer climate, (2) the permafrost ice-table did not significantly influence valley network width-to-depth ratios, possibly owing to more rapid thermal erosion rates than mechanical, or (3) additional factors not accounted for in this analysis are involved. Potential additional factors which could influence the results of this analysis include variable surface geothermal heat flux, substrate thermal conductivity, substrate composition and physical state as well as valley network preservation state, and morphometric sampling biases (due to data availability constraints). These factors represent areas for future investigation to refine assessments of valley network formation under cold early Mars conditions.

Thermal Properties of Icy Surfaces in the Outer Solar System

The thermal properties of airless icy surfaces are providing a wealth of information on their regolith structure after eons of space weathering. Numerous observations of the thermal cycles of Jupiter and Saturn icy satellites or Centaurs and TNOs have been acquired in the latest decades thanks to the Galileo and Cassini missions and to the Spitzer and Herschel telescopes. These observations and the latest developments on thermophysical modeling which have been achieved to link the thermal inertia to the regolith structure are reviewed here. Measured thermal inertias of these surfaces covered with water ice are very low, roughly between about 1 and 100 J/m2/K/s1/2. Often interpreted as due to unconsolidated or highly porous regoliths, these low values may result from a composition of amorphous ice or from the roughness of grains defacing contacts in a regolith of normal compaction. Taken together, thermal inertias appear to increase with probed depth and to decrease with heliocentric distance. This latter effect can be easily reproduced if heat transfer is dominated by radiation in pores, despite low temperatures, because the conduction through grains is limited, either due to the presence of amorphous ice or because of the roughness of grains.

Dust Motions in Magnetized Turbulence: Source of Chemical Complexity

Abstract In addition to the manufacture of complex organic molecules from impacting cometary and icy planet surface analogs, which is well-established, dust grain–grain collisions driven by turbulence in interstellar or circumstellar regions may represent a parallel chemical route toward the shock synthesis of prebiotically relevant species. Here we report on a study, based on the multi-scale shock-compression technique combined with ab initio molecular dynamics approaches, where the shock-wave-driven chemistry of mutually colliding isocyanic acid (HNCO) containing icy grains has been simulated by first principles. At the shock-wave velocity threshold triggering the chemical transformation of the sample (7 km s−1), formamide is the first synthesized species, thus being the springboard for the further complexification of the system. Also, upon increasing the shock impact velocity, formamide is formed in progressively larger amounts. More interestingly, at the highest velocity considered (10 km s−1), impacts drive the production of diverse carbon–carbon bonded species. In addition to glycine, the building block of alanine (i.e., ethanimine) and one of the major components of a plethora of amino acids including, e.g., asparagine, cysteine, and leucine (i.e., vinylamine), have been detected after shock compression of samples containing the most widespread molecule in the universe (H2) and the simplest compound bearing all of the primary biogenic elements (HNCO). The present results indicate novel chemical pathways toward the chemical complexity typical of interstellar and circumstellar regions.

Polarimetry of Water Ice Particles Providing Insights on Grain Size and Degree of Sintering on Icy Planetary Surfaces

AbstractThe polarimetry of the light scattered by planetary surfaces is a powerful tool to provide constraints on their microstructure. To improve the interpretation of polarimetric data from icy surfaces, we have developed the POLarimeter for ICE Samples complementing the measurement facilities of the Ice Laboratory at the University of Bern. The new setup uses a high precision Stokes polarimeter to measure the degree of polarization in the visible light scattered by surfaces at moderate phase angles (from 1.5° to 30°). We present the photometric and polarimetric phase curves measured on various surfaces made of pure water ice particles having well‐controlled size and shape (spherical, crushed, and frost). The results show how the amplitude and the shape of the negative polarization branch change with the particles sizes and the degree of metamorphism of the ice. We found that fresh frost formed by water condensation on cold surfaces has a phase curve characterized by resonances (Mie oscillations) indicating that frost embryos are transparent micrometer‐sized particles with a narrow size distribution and spherical shape. Comparisons of these measurements with polarimetric observations of the icy satellites of the Solar System suggest that Europa is possibly covered by relatively coarser (~40–400 μm) and more sintered grains than Enceladus and Rhea, more likely covered by frost‐like particles of few micrometers in average. The great sensitivity of polarization to grain size and degree of sintering makes it an ideal tool to detect hints of ongoing processes on icy planetary surfaces, such as cryovolcanism.

Testing S isotopes as biomarkers for Mars

AbstractWe suggest testing S isotopes as biomarkers for Mars. An analogous robust biosignature has recently been proposed for the forthcoming exploration of the icy surface of Europa, and in the long term for the exploration of the surfaces of other icy moons of the outer solar system. We discuss relevant instrumentation for testing the presence of life itself in some sites, whether extinct or extant in order to complement a set of other independent biosignatures. We pay special attention to the possible early emergence of sulphate-metabolizing microorganisms, as it happened on the early Earth. Fortunately, possible sites happen to be at likely landing sites for future missions ExoMars and Mars 2020, including Oxia Planum and Mawrth Vallis. We suggest how to make additional feasible use of the instruments that have already been approved for future missions. With these instruments, the proposed measurements can allow testing S isotopes on Mars, especially with the Mars Organic Molecule Analyzer.

Ocean Worlds in the Outer Regions of the Solar System (Review)

There is an astonishing variety of celestial bodies in the outer regions of the Solar System: Europa, with its bizarre surface features, Enceladus, small but geologically active, Titan, the only moon with a significant atmosphere, Pluto, with its nitrogen glaciers, and many others. Over the past 25 years, measurements from spacecraft have shown that many of these celestial bodies are ocean worlds with large volumes of liquid water trapped under icy surfaces. This new group of celestial bodies, ocean worlds, is important for research for several reasons, but the most convincing and at the same time the simplest reason is that they can be potential habitats. Life, as we know it, requires liquid water in addition to energy, nutrients, and a sustainable environment. All these requirements can be met for some of these celestial bodies. The moons of the giant planets on which the presence of the subsurface ocean is established (Europa, Ganymede, Titan, and Enceladus) and their astrobiological potential are discussed.

Patterns of Traffic Accidents Among Elderly Pedestrians in Sweden

The objective of this study is to characterize the nature and space-time patterns of traffic accidents involving elderly pedestrians in Sweden, in order to suggest preventive measures. The analysis is based on elderly pedestrian accidents from 2010 to 2014 using an age adjusted standardized elderly accidents ratios (ASEAR), Geographical Information Systems (GIS) and spatial statistics techniques. Findings show that the geography of elderly traffic accidents is far from being homogenous across the country: although most accidents happen in urban municipalities, 30 per cent of municipalities classified as accessible rural exhibit relatively high-standardized accidents ratios. They happen often in daylight hours, on weekdays and in the coldest months of the year. Most of the cases are single accidents (e.g. self-inflicted fall); they happen in street segments/intersections and pedestrian/bicycle path, some affected by environment conditions such as icy or uneven surfaces. Findings of the study call for preventive actions that are sensitive to the nature of these accidents in different temporal and spatial contexts.

Morphological mapping of Ganymede: Investigating the role of strike-slip tectonics in the evolution of terrain types

The heavily fractured surface of Ganymede displays many morphologically distinctive regions of inferred distributed shear and strike-slip faulting that may be important to the structural development of its surface. To better understand the role of strike-slip tectonism in shaping this complex icy surface, we perform detailed mapping at nine sites using Galileo and Voyager imagery, noting key examples of strike-slip morphologies where present. These four morphological indicators are: en echelon structures, strike-slip duplexes, laterally offset pre-existing features, and possible strained craters. We map sites of both light, grooved terrain (Nun Sulci, Dardanus Sulcus, Tiamat Sulcus, Uruk Sulcus, and Arbela Sulcus), and terrains that are transitional from dark to light terrains (Nippur and Philus Sulci, Byblus Sulcus, Anshar Sulcus, and the Transitional Terrain of Northern Marius Regio). At least one, if not more, of the four strike-slip morphological indicators are observed at every site, suggesting strike-slip tectonism is indeed important to Ganymede's evolutionary history. Byblus Sulcus is the only mapped site where the presence of strike-slip indicators is limited to only a few en echelon structures; every other mapped site displays examples of at least two types, with Arbela Sulcus containing candidate examples of all four. In addition, quantification of morphological characteristics suggests related rotation between sites, as evidenced by the predominant NW/SE trend of mapped features within the light terrain present in five different sites (Nun, Tiamat, Uruk, Nippur/Philus, Byblus, and Anshar Sulcus). Moreover, incorporation of strike-slip tectonism with pre-existing observations of extensional behavior provides an improved, synoptic representation of Ganymede's tectonic history.

Band Formation and Ocean‐Surface Interaction on Europa and Ganymede

AbstractGeologic activity in the outer H2O ice shells of Europa and Ganymede, Galilean moons of Jupiter, may facilitate material exchange between global water oceans and the icy surface, fundamentally affecting potential habitability and the future search for life. Spacecraft imagery reveals surfaces rich with tectonic bands, predominantly attributed to the extension of brittle ice overlaying a convecting ice layer. However, the details of band‐forming processes and links to potential ocean‐surface exchange have remained elusive. We simulate ice shell faulting and convection with two‐dimensional numerical models and track the movement of “fossil” ocean material frozen into the base of the ice shell and deformed through geologic time. We find that distinct band types form within a spectrum of extensional terrains correlated to lithosphere strength, governed by lithosphere thickness and cohesion. Furthermore, we find that smooth bands formed in weak lithosphere promote exposure of fossil ocean material at the surface.

Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures

The icy surface of Jupiter’s moon, Europa, is thought to lie on top of a global ocean1–4. Signatures in some Hubble Space Telescope images have been associated with putative water plumes rising above Europa’s surface5,6, providing support for the ocean theory. However, all telescopic detections reported were made at the limit of sensitivity of the data5–7, thereby calling for a search for plume signatures in in-situ measurements. Here, we report in-situ evidence of a plume on Europa from the magnetic field and plasma wave observations acquired on Galileo’s closest encounter with the moon. During this flyby, which dropped below 400 km altitude, the magnetometer 8 recorded an approximately 1,000-kilometre-scale field rotation and a decrease of over 200 nT in field magnitude, and the Plasma Wave Spectrometer 9 registered intense localized wave emissions indicative of a brief but substantial increase in plasma density. We show that the location, duration and variations of the magnetic field and plasma wave measurements are consistent with the interaction of Jupiter’s corotating plasma with Europa if a plume with characteristics inferred from Hubble images were erupting from the region of Europa’s thermal anomalies. These results provide strong independent evidence of the presence of plumes at Europa.

Europa’s ice-related atmosphere: The sputter contribution

Europa, Jupiter’s innermost icy satellite, is embedded well within Jupiter’s magnetospheric plasma, an intense flux of ions and electrons that approximately co-rotate with Jupiter. The plasma can be thought of as consisting of two populations: The cold, thermal plasma containing charged particles with energies ranging from 1 eV to 1 keV, and the hot, energetic plasma containing charged particles with energies ranging from 10 keV to 100 MeV. When the charged particles interact with Europa’s surface, they not only chemically and physically alter the icy surface, but also liberate material from the surface through a process called sputtering, which in turn forms a tenuous atmosphere.In this paper we calculate the sputter contribution to the atmosphere by modeling the formation of Europa’s ice-sputtered atmosphere ab initio. We consider the species H, H2, O, OH, H2O, O2, HO2, H2O2, and O3, all of which are related to the water–ice surface. Whereas the ice sputter yields of H2O, H2, and O2 have been well established, the ice sputter yields (and the resulting density profiles) of H, O, OH, HO2 and O3 are small and largely unknown. As model input we use available plasma ion and electron energy spectra as well as available water-ice sputter yields. Based on first principles, i.e., without applying any scaling to observed data, we calculate atmospheric densities ab initio.Our results match available observational data and previously published modeling efforts well. Europa’s exosphere is dominated by thermally accommodated O2 close to the surface (below a few 100 km), and the much lighter H2 molecules at higher altitudes. The water-ice related species that stick to the surface (freeze out) are liberated by cold and hot plasma sputtering in about equal amounts. In addition, in the case of H2, O2, and H2O2, electrons contribute almost as significantly to the sputter yield as ions do.