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Predicting transport rates of windblown sand is a central problem in aeolian research, with implications for climate, environmental, and planetary sciences. Though studied since the 1930s, the underlying many-body dynamics is still incompletely understood, as underscored by the recent empirical discovery of an unexpected third-root scaling in the particle-fluid density ratio. Here, by means of grain-scale simulations and analytical modeling, we elucidate how a complex coupling between grain-bed collisions and granular creep within the sand bed yields a dilatancy-enhanced bed erodibility. Our minimal saltation model robustly predicts both the observed scaling and a new undersaturated steady transport state that we confirm by simulations for rarefied atmospheres.

Iron (Fe) is an essential micronutrient in glacial ecosystems and modulates global biogeochemical cycles. To find out the deposition concentration, multiple origins and release form of iron in various glacier areas of central Asia, this study investigated the total Fe (TFe) and dissolved-Fe (dFe, diameter < 0.45 or <0.2 μm) deposition in glaciers and snowpack of northeast Tibetan Plateau, based on snow and meltwater sampling in ablation period of 2014-2017. The composition and concentration of dFe in the samples were measured, and the spatial distribution and temporal variations of dFe in glacial surface snow and meltwater runoff were investigated. Results showed that average TFe and dFe contents exhibited a generally heterogeneous geographic distribution that varied from north to south. The northern locations in eastern Tianshan Mountains (e.g. Miaoergou Glacier) showed the highest TFe and dFe values, followed by Yuzhufeng Glacier of eastern Kunlun Mountains, whereas the Qilian Mountains locations displayed relatively lower TFe and dFe contents spanning a wide range. Based on the good correlation between TFe and dFe, we infer that aeolian dust and anthropogenic aerosols, and their chemical interactions are likely the important origins for dFe deposition. In meltwater runoff the peak values of dFe release flux appeared in July, with maximum appeared earlier (the early of July) than TFe (the end of July). Moreover, the annual dFe release flux from Laohugou glacier terminus meltwater runoff is estimated to be 1740 kg yr -1 (with 9256 kg yr -1 for TFe), and meltwater showed higher mean concentration of dFe than that of glacier snowpack. We also provided a conceptual framework showing the multiple origins and transport dynamics of dissolved Fe along the atmosphere-glacier-meltwater runoff path. Compared to Fe release in other global glacier/ice-sheet, the TP glacier is an important potential dFe reservoir and may have a profound effect on regional downstream ecosystem through Fe biochemistry cycle., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The angle of repose-i.e., the angle [Formula: see text] between the sloping side of a heap of particles and the horizontal-provides one of the most important observables characterizing the packing and flowability of a granular material. However, this angle is determined by still poorly understood particle-scale processes, as the interactions between particles in the heap cause resistance to roll and slide under the action of gravity. A theoretical expression that predicts [Formula: see text] as a function of particle size and gravity would have impact in the engineering, environmental, and planetary sciences. Here we present such an expression, which we have derived from particle-based numerical simulations that account for both sliding and rolling resistance, as well as for nonbonded attractive particle-particle interactions (van der Waals). Our expression is simple and reproduces the angle of repose of experimental conical heaps as a function of particle size, as well as [Formula: see text] obtained from our simulations with gravity from 0.06 to 100 times that of Earth. Furthermore, we find that heaps undergo a transition from conical to irregular shape when the cohesive to gravitational force ratio exceeds a critical value, thus providing a proxy for particle-scale interactions from heap morphology., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

The surface of Pluto is more geologically diverse and dynamic than had been expected, but the role of its tenuous atmosphere in shaping the landscape remains unclear. We describe observations from the New Horizons spacecraft of regularly spaced, linear ridges whose morphology, distribution, and orientation are consistent with being transverse dunes. These are located close to mountainous regions and are orthogonal to nearby wind streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes, and relationships with the underlying convective glacial ice, imply that the dunes have formed in the very recent geological past., (Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

When a thin tube is dipped into water, the water will ascend to a certain height, against the action of gravity. While this effect, termed capillarity, is well known, recent experiments have shown that agitated granular matter reveals a similar behavior. Namely, when a vertical tube is inserted into a container filled with granular material and is then set into vertical vibration, the particles rise up along the tube. In the present Letter, we investigate the effect of granular capillarity by means of numerical simulations and show that the effect is caused by convection of the granular material in the container. Moreover, we identify two regimes of behavior for the capillary height H&#95;{c}^{∞} depending on the tube-to-particle-diameter ratio, D/d. For large D/d, a scaling of H&#95;{c}^{∞} with the inverse of the tube diameter, which is reminiscent of liquids, is observed. However, when D/d decreases down to values smaller than a few particle sizes, a uniquely granular behavior is observed where H&#95;{c}^{∞} increases linearly with the tube diameter.