The role of Jupiter in driving Earth’s orbital evolution: an update

In the coming decades, the discovery of the first truly Earth-like exoplanets is anticipated. The characterisation of those planets will play a vital role in determining which are chosen as targets for the search for life beyond the Solar system. One of the many variables that will be considered in that characterisation and selection process is the nature of the potential climatic variability of the exoEarths in question. In our own Solar system, the Earth’s long-term climate is driven by several factors – including the modifying influence of life on our atmosphere, and the temporal evolution of Solar luminosity. The gravitational influence of the other planets in our Solar system add an extra complication – driving the Milankovitch cycles that are thought to have caused the ongoing series of glacial and interglacial periods that have dominated Earth’s climate for the past few million years. Here, we present the results of a large suite of dynamical simulations that investigate the influence of the giant planet Jupiter on the Earth’s Milankovitch cycles. If Jupiter was located on a different orbit, we find that the long-term variability of Earth’s orbit would be significantly different. Our results illustrate how small differences in the architecture of planetary systems can result in marked changes in the potential habitability of the planets therein, and are an important first step in developing a means to characterise the nature of climate variability on planets beyond our Solar system

An inversion approach for analysing the physical properties of a seismic low-velocity layer in the upper mantle

International audienceIn this article, we propose a new inversion scheme to calculate the melt volume 17 fractions from observed seismic anomalies in a low-velocity layer (LVL) located atop 18 the mantle transition zone. Our method identifies the trade-offs in the seismic 19 signature caused by temperature, solid composition, melt volume fraction, and 20 dihedral angle at the solid-melt interface. Using the information derived from the 2

Subsurface Flow Batteries:Concept, Benefits and Hurdles

Storage of flow-battery electrolytes in aquifers is a novel concept for storing electrical energy in the subsurface. Flow-batteries operate by electrochemical transformations of electrolytes, rather than of electrodes, and their energy capacity can therefore be increased indefinitely by using larger electrolyte tanks. Saline aquifers may be the cheapest way to provide large-scale storage for this purpose. Storage would be within high-porosity, high-permeability reservoirs sealed by impermeable layers but—in contrast to hydrocarbon, H2 or CO2 storage—electrolytes would be trapped in lows (rather than highs) of such formations as a consequence of their high density compared to natural brines.We investigate a range of electrochemical, geochemical, microbiological and engineering hurdles which must be overcome if subsurface flow-batteries are to become a practical technology. No insurmountable problems were found but further laboratory studies are needed. Our economic assessment suggests that subsurface flow batteries should be more cost effective than hydrogen-based power-to-gas approaches for discharge/charge timescales of around a day but that hydrogen will be cheaper for longer-term storage. Hence, meeting future energy-storage needs may involve a combination of both approaches

Enabling planetary science across light-years. Ariel Definition Study Report

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution

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Analogue modelling of pyroclastic density current deposition

A series of analogue flume experiments are used to investigate initiation, flow and deposition of static piles of polymict materials, the sorting during transport, and the three dimensional geometry of the resulting deposits. Sequential charges are used to investigate the effects and extent of reworking. The particle heterogeneity is designed to simulate typical PDC make-up, with analogues for juvenile pumice and lithic clasts, as well as the fine-grained pumiceous material which makes up the bulk of the flow. Analogue flume experiments are used to investigate the generation of complex facies variations typical of pyroclastic density current (PDC) deposits. Polymict charges are developed to behave as analogues for the particle size and density contrasts present in PDC (i.e. lithic and juvenile pumice clasts), and investigate the effect of granular sorting during flow on the geometry of deposit architectures. Multiple charges are used to simulate pulses or sequences of separate PDC in order to assess the extent and effects of reworking. 3D visualisation of the resulting deposits reveals stratigraphies analogous to those seen in PDC, including pumice ‘rafting' or over-passing and inverse grading of pumice, and normal grading of lithics by simple gravitational granular sorting. Reworking between differentially-coloured layers makes several complex shear-derived Kelvin-Helmholtz instability features apparent, from fully developed rotational eddies, to less developed recumbent flame structures. The implications for the formation of these in PDC are assessed, including the potential influences on temperature proxy data, radiogenic dating by included phenocrysts (40Ar/39Ar) or charcoals (14C), calculation of eruptive volumes, sedimentation rates and flow velocity.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Shear-derived mixing in dense granular flows

In flume experiments, granular avalanches run onto loose substrates develop 3-D architectures that record shear-derived mixing between the flow and the substrate. Spherical silica beads 0.250 mm diameter are run onto stratified substrates of various topographies composed of identical but colored materials. A method of setting and serial sectioning experimental granular deposits is presented. Experiments investigating the interactions between these granular charges and substrates reveal that centimeter-scale vortical reworking features are produced by the highly unsteady flows, with localized erosion depth of the same order as the flow thickness. The structure of the reworking features indicates predominantly bed-normal and streamwise particle motions and is interpreted as most likely to reflect velocity-shear instability growth, similar to Kelvin-Helmholtz instabilities formed in Newtonian fluids. This constitutes the first observation of such features formed within granular fluids by motions within the vertical plane. The scale of the features and degree of mixing generated by them has implications for the reliability of stratigraphic interpretations of geophysical granular flow deposits, such as those formed by debris avalanches and pyroclastic density currents. Sheared "flame structures" commonly observed at the bases of geophysical flow deposits might be explained in some cases by reworking by unsteady currents, or by rapid vertical migration of the active shear zone in long-lived steady currents. Copyright © 2011, SEPM (Society for Sedimentary Geology)