How the Enceladus dust plume feeds Saturn’s E ring

Pre-Cassini models of Saturn’s E ring [Horányi, M., Burns, J., Hamilton, D., 1992. Icarus 97, 248-259; Juhász, A., Horányi, M., 2002. J. Geophys. Res. 107, 1-10] failed to reproduce its peculiar vertical structure inferred from Earth-bound observations [de Pater, I., Martin, S.C., Showalter, M.R., 2004. Icarus 172, 446-454]. After the discovery of an active ice-volcanism of Saturn’s icy moon Enceladus the relevance of the directed injection of particles for the vertical ring structure of the E ring was swiftly recognised [Juhász, A., Horányi, M., Morfill, G.E., 2007. Geophys. Res. Lett. 34, L09104; Kempf, S., Beckmann, U., Moragas-Klostermeyer, G., Postberg, F., Srama, R., Economou, T., Schmidt, J., Spahn, F., Grün, E., 2008. Icarus 193, 420-437]. However, simple models for the delivery of particles from the plume to the ring predict a too small vertical ring thickness and overestimate the amount of the injected dust.Here we report on numerical simulations of grains leaving the plume and populating the dust torus of Enceladus. We run a large number of dynamical simulations including gravity and Lorentz force to investigate the earliest phase of the ring particle life span. The evolution of the electrostatic charge carried by the initially uncharged grains is treated selfconsistently. Freshly ejected plume particles are moving in almost circular orbits because the Enceladus orbital speed exceeds the particles’ ejection speeds by far. Only a small fraction of grains that leave the Hill sphere of Enceladus survive the next encounter with the moon. Thus, the flux and size distribution of the surviving grains, replenishing the ring particle reservoir, differs significantly from the flux and size distribution of the particles freshly ejected from the plume. Our numerical simulations reproduce the vertical ring profile measured by the Cassini Cosmic Dust Analyzer (CDA) [Kempf, S., Beckmann, U., Moragas-Klostermeyer, G., Postberg, F., Srama, R., EconoDmou, T., Smchmidt, J., Spahn, F., Grün, E., 2008. Icarus 193, 420-437]. From our simulations we calculate the deposition rates of plume particles hitting Enceladus’ surface. We find that at a distance of 100 m from a jet a 10 m sized ice boulder should be covered by plume particles in 10⁵-10⁶ years.     

Numerical simulation of three-dimensional saltwater–freshwater fingering instabilities observed in a porous medium

We consider saltwater–freshwater fingering instabilities in a saturated porous medium. In the first part, we present three-dimensional results obtained from a laboratory experiment using non-invasive imaging. In the second part, we define a set of model problems in which the performed laboratory experiments can be ranged in. Due to its highly non-linear behavior and inevitable modeling errors, a detailed numerical reproduction of the physical concentration measurements cannot be expected. Nevertheless, four criteria have been identified, two quantitative and two qualitative, which facilitate a substantiated comparison of the physical experiment and the numerical simulation. With respect to these criteria a high degree of similarity could be observed. The use of these features allows a deeper understanding of the physical processes and the influence of the initial conditions.     

Late Cretaceous eclogite in the Eastern Rhodopes (Bulgaria): evidence for subduction under the Sredna Gora magmatic arc

International Journal of Earth Sciences - The Rhodopes in Bulgaria and Greece represent a nappe stack of high-grade units with polymetamorphic history. Constraining the time of metamorphism in...     

Numerical investigation of soil plugging inside open-ended piles with respect to the installation method

The development of a soil plug inside an open-ended pile with respect to the installation method is examined using numerical simulations. In this paper, the penetration process of an open-ended tubular pile with diameter D = 61 cm into granular soil is investigated. The aim is to achieve a better understanding of the mechanisms of soil plugging inside open-ended piles with respect to the installation method. As an example, the horizontal stress distribution inside the tubular pile after installation shows significant increase depending on the installation method. The numerical results are compared to experimental data.     

Uncertainty management and the dynamic adjustment of deep decarbonization pathways

Contrary to ‘static’ pathways that are defined once for all, this article deals with the need for policy makers to adopt a dynamic adaptive policy pathway for managing decarbonization over the period of implementation. When choosing a pathway as the most desirable option, it is important to keep in mind that each decarbonization option relies on the implementation of specific policies and instruments. Given structural, effectiveness, and timing uncertainties specific to each policy option, they may fail in delivering the expected outcomes in time. The possibility of diverging from an initial decarbonization trajectory to another one without incurring excessive costs should therefore be a strategic element in the design of an appropriate decarbonization strategy. The article relies on initial experiences in France and Germany on decarbonization planning and implementation to define elements for managing dynamic adjustment issues. Such an adaptive pathway strategy should combine long-lived incentives, like a pre-announced escalating carbon price, to form consistent expectations, as well as adaptive policies to improve overall robustness and resilience. We sketch key elements of a monitoring process based on an ex ante definition of leading indicators that should be assessed regularly and combined with signposts and trigger values at the subsector level.

Policy relevance

These research questions are of special interest and urgency following the Paris Agreement in 2015. It calls on all countries to monitor the implementation of their national contributions and review their ambition regularly. The regular revision of decarbonization pathways constitute a great research opportunity to gather experiences on decarbonization pathway implementation and on dynamic management issues to progress towards an operational dynamic adaptive policy pathway mechanism.     

The Impact of Global/Local Bias on Task-Solving in Map-Related Tasks Employing Extrinsic and Intrinsic Visualization of Risk Uncertainty Maps

The form of visual representation affects both the way in which the visual representation is processed and the effectiveness of this processing. Different forms of visual representation may require the employment of different cognitive strategies in order to solve a particular task; at the same time, the different representations vary as to the extent to which they correspond with an individual’s preferred cognitive style. The present study employed a Navon-type task to learn about the occurrence of global/local bias. The research was based on close interdisciplinary cooperation between the domains of both psychology and cartography. Several different types of tasks were made involving avalanche hazard maps with intrinsic/extrinsic visual representations, each of them employing different types of graphic variables representing the level of avalanche hazard and avalanche hazard uncertainty. The research sample consisted of two groups of participants, each of which was provided with a different form of visual representation of identical geographical data, such that the representations could be regarded as ‘informationally equivalent’. The first phase of the research consisted of two correlation studies, the first involving subjects with a high degree of map literacy (students of cartography) (intrinsic method: N?=?35; extrinsic method: N?=?37). The second study was performed after the results of the first study were analyzed. The second group of participants consisted of subjects with a low expected degree of map literacy (students of psychology; intrinsic method: N?=?35; extrinsic method: N?=?27).The first study revealed a statistically significant moderate correlation between the students’ response times in extrinsic visualization tasks and their response times in a global subtest (r?=?0.384, p?<?0.05); likewise, a statistically significant moderate correlation was found between the students’ response times in intrinsic visualization tasks and their response times in the local subtest (r?=?0.387, p?<?0.05). At the same time, no correlation was found between the students’ performance in the local subtest and their performance in extrinsic visualization tasks, or between their scores in the global subtest and their performance in intrinsic visualization tasks. The second correlation study did not confirm the results of the first correlation study (intrinsic visualization/‘small figures test’: r?=?0.221; extrinsic visualization/‘large figures test’: r?=?0.135). The first phase of the research, where the data was subjected to statistical analysis, was followed by a comparative eye-tracking study, whose aim was to provide more detailed insight into the cognitive strategies employed when solving map-related tasks. More specifically, the eye-tracking study was expected to be able to detect possible differences between the cognitive patterns employed when solving extrinsic- as opposed to intrinsic visualization tasks. The results of an exploratory eye-tracking data analysis support the hypothesis of different strategies of visual information processing being used in reaction to different types of visualization.     

Interplanetary dust detected by the Cassini CDA Chemical Analyser

During its cruise phase, prior to encountering Jupiter, the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft returned time of flight mass spectra (TOF MS) of two interplanetary dust particles. Both particles were found to be iron-rich, with possible traces of hydrogen, carbon, nickel, chromium, manganese, titanium, vanadium and minor silicates. Carbon, hydrogen, oxygen and potassium are also present as possible contaminants of the impact target of CDA. Silicates and magnesium do not feature predominantly in the spectra; this is surprising considering the expected dominance of silicate-rich minerals in interplanetary dust particles. The particle masses are and . The corresponding radii ranges for the particles, assuming densities from 7874-2500 kg m⁻³ are 0.7-4 μm and 2.6-6.8 μm, respectively. With the same density assumptions the β values (ratio of radiation pressure to gravitational force) are estimated as 0.027-0.21 and 0.016-0.06 respectively, allowing possible orbits to be calculated. The resulting orbits are bound and prograde with semi-major axes, eccentricities and inclinations in the region of 0.3-1.26 AU, 0.4-1.0 and 0-60° for the first particle and 0.8-2.5 AU, 0.2-0.9 and 0-30° for the second. The more probable orbits within these ranges indicate that the first particle is in an Aten-like orbit, whilst the second particle is in an Apollo-like orbit, despite both grains having very similar, predominantly metallic compositions. Other possible orbital solutions for both particles encompass orbits which more closely resemble those of Jupiter-family comets.     

Sample return of interstellar matter (SARIM)

The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We propose a new mission concept, SARIM, that collects interstellar and interplanetary dust particles and returns them to Earth. SARIM is optimised for the collection and discrimination of interstellar dust grains. Improved active dust collectors on-board allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important constraints for subsequent laboratory analysis. The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and inside the solar-wind charging environment. SARIM is three-axes stabilised and collects interstellar grains between July and October when the relative encounter speeds with interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection period several hundred interstellar and several thousand interplanetary grains will be collected by a total sensitive area of 1 m². At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule. SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of interstellar samples by latest laboratory technologies.