Craters as sand traps: Dynamics, history, and morphology of modern sand transport in an active Martian dune field

Aeolian transport of sand is abundant on modern-day Mars, as revealed by remote sensing measurements of the motion of dunes, and of the meter-scale ripples that mantle them. We study a large-scale natural sand trap within the Meroe Patera dune field: a 1.8-km diameter crater which features a dune-free “shadow” in its lee. We compare the volume of sand trapped within this crater to the sand volume that would be expected to cover the area of the crater and its dune-free shadow behind it if the crater were not present. We find that the crater holds less sand than this “missing” volume would predict, implying that sand escapes from the crater over time. Modern day imagery shows an apparent lack of sand escaping from the Meroe crater, however, suggesting that changes in the wind regime at the site may have allowed sand to escape in the past. The persistence of an altered dune morphology all the way to the far downwind edge of the dune field suggests consistent wind conditions over the time of the crater-dune field interaction

Craters as sand traps: Dynamics, history, and morphology of modern sand transport in an active Martian dune field

Aeolian transport of sand is abundant on modern-day Mars, as revealed by remote sensing measurements of the motion of dunes, and of the meter-scale ripples that mantle them. We study a large-scale natural sand trap within the Meroe Patera dune field: a 1.8-km diameter crater which features a dune-free “shadow” in its lee. We compare the volume of sand trapped within this crater to the sand volume that would be expected to cover the area of the crater and its dune-free shadow behind it if the crater were not present. We find that the crater holds less sand than this “missing” volume would predict, implying that sand escapes from the crater over time. Modern day imagery shows an apparent lack of sand escaping from the Meroe crater, however, suggesting that changes in the wind regime at the site may have allowed sand to escape in the past. The persistence of an altered dune morphology all the way to the far downwind edge of the dune field suggests consistent wind conditions over the time of the crater-dune field interaction

Lunar International Science Coordination/Calibration Targets

A new era of international lunar exploration has begun and will expand over the next four years with data acquired from at least four sophisticated remote sensing missions: KAGUYA (SELENE) [Japan], Chang'E [China], Chandrayaan-l [India], and LRO [United States]. It is recognized that this combined activity at the Moon with modern sophisticated sensors wi II provide unprecedented new information about the Moon and will dramatically improve our understanding of Earth's nearest neighbor. It is anticipated that the blooming of scientific exploration of the Moon by nations involved in space activities will seed and foster peaceful international coordination and cooperation that will benefit all. Summarized here are eight Lunar International Science Coordination/Calibration Targets (L-ISCT) that are intended to a) allow cross-calibration of diverse multi-national instruments and b) provide a focus for training young scientists about a range of lunar science issues. The targets, discussed at several scientific forums, were selected for coordinated science and instrument calibration of orbital data. All instrument teams are encouraged to participate in a coordinated activity of early-release data that will improve calibration and validation of data across independent and diverse instruments

Lewis number effects on lean premixed combustion characteristics of multi-component fuel blends

Variation in natural gas composition, alongside the potential for H2 enrichment, creates the potential for significant changes to premixed flame behaviour. To strengthen fundamental understanding of lean multi-component alternative fuel blends, an outwardly propagating spherical flame was employed to measure the flame speeds and Markstein lengths of C1single bondC4 hydrocarbons, alongside precisely mixed blends of CH4/C2H6, CH4/C3H8 and CH4/H2. Theoretical relationships between Markstein length and Lewis Number are explored alongside effective Lewis number formulations. Under lean conditions, equal volumetric additions of H2 and C3H8 (30% vol.) to CH4 resulted in similar augmentation of burning velocity, however, opposite susceptibility to preferential diffusional instability was noted. At a fixed equivalence ratio of 0.65, limited changes in composition provide a marked change in the premixed flame response with the addition of C2H6 and C3H8 to CH4. For lean CH4/H2 mixtures, a diffusional based Lewis Number formulation yielded a favourable correlation, whilst a heat-release model resulted in better agreement for lean CH4/C3H8 blends. Modelling work suggests that measured enhancement of lean CH4 flames upon H2 or C3H8 is strongly correlated to changes in volumetric heat release rates and production of H radicals. Furthermore, a systematic analysis of the flame speed enhancement effects (thermal, kinetic, diffusive) of H2 and C3H8 addition to methane was undertaken. Augmented flame propagation of CH4/H2 and CH4/C3H8 was demonstrated to be principally an Arrhenius effect, predominantly through reduction of associated activation energy. Finally, plausible short-term variations in composition with hydrogen-enriched multi-component natural gas flames were investigated experimentally and numerically. At the leanest conditions, small variations in CH4:C3H8 content at a fixed H2 fraction resulted in discernible changes in stretch related behaviour, a reflection of the thermo-diffusive behaviour of each fuel's response

Integrated analysis of topographically high Mafic exposures at Apollo-17 landing site using data from imaging sensors of Chandrayaan-1

This article does not have an abstract

Curie: Constraining Solar System Bombardment Using In Situ Radiometric Dating

The Curie mission would constrain the existence of the putative cataclysm by determining the age of samples directly sourced from the impact melt sheet of a major pre-Imbrium lunar basin. The measurements would also enable further understanding of lunar evolution by characterizing new lunar lithologies far from the Apollo and Luna landing sites, including the very low-Ti basalts in Mare Crisium and potential olivine rich lithologies in the margins of both Mare Nectaris and Mars Crisium. Equipped with a mass spectrometer and a LIBS, Curie would also be well-placed to survey volatile components of the lunar regolith, including surface-bound hydrogen

Pluto's Far Side

The New Horizons spacecraft provided near-global observations of Pluto that far exceed the resolution of Earth-based datasets. However, most previous Pluto New Horizons analyses focused on the New Horizons encounter hemisphere (i.e., the anti-Charon hemisphere containing Sputnik Planitia). In this work, we summarize and interpret data on Pluto's “far side” (i.e., its non-encounter or alternatively, its sub-Charon hemisphere), providing the first integrated New Horizons overview of Pluto's far side terrains. We find strong evidence for widespread bladed (i.e., aligned CH₄-mountain) deposits, evidence for an impact crater about as large as any on the “near side” hemisphere, evidence for complex lineations approximately antipodal to Sputnik Planitia that may be causally related, evidence that the far side maculae (i.e., equatorial dark regions) are smaller and more structured than Pluto's encounter hemisphere maculae, and more

Dissociative influence of H2O vapour/spray on lean blowoff and NOx reduction for heavily carbonaceous syngas swirling flames

Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O with heavily carbonaceous syngas mixtures. In this study, the potential benefits of these subtle changes in water loading and hence reaction pathways are explored in terms of delayed lean blowoff, and primary emission reduction in a premixed turbulent swirling flame (Ø = 0.6–0.8), scaled for practical relevance. Chemical kinetic models initially confirm that H2O has a substantial impact on the employed fuel behaviour; increasing flame speed by up to 60% across an experimental range representative of fluctuation in atmospheric humidity (∼1.8 mol%). OH* chemiluminescence and OH planar laser induced fluorescence (PLIF) were employed to analyse the changes in heat release structure resulting from the experimental addition of H2O vapour to the combustor. Equivalent concentrations of liquid H2O were introduced into the central recirculation zone of the premixed flame as an atomised spray, to investigate the influence of phase changes on the catalytic effect. Near the lean stability limit, H2O addition compresses heat release to shorten the elongated flame structure. Whereas with a stable and well-defined flame structure, the addition triggers a change in axial heat release location, causing the flame front to retract upstream toward the burner outlet. Higher quantities of two-phase flow were combined to explore the possibility of employing the spray as a stabilising mechanism, effectively dampening the observed influence of humidity. The chemical enhancement induced by the controlled supply was shown to reduce the lean blowoff stability limit, enabling an increase in additional air flow of almost 10%. However, the catalytic effect of H2O diminishes with excessive supply and thermal quenching prevails. There is a compound benefit of NOx reduction from the use of H2O as a flame stabiliser with the practically-relevant syngas: First NOx production decreases due to thermal effect of H2O addition, with potential for further reduction from the change in lean stability limit; leanest experimental concentrations reduced by up to a factor of four with two-phase flow at the highest rates of supply. Hence, the catalytic effect of H2O on reaction pathways and reaction rate predicted and observed in the laminar environment, is shown to translate into practical benefits in the challenging environment of turbulent, swirl-stabilised flames

Mineralogy of the Lunar Crust in Spatial Context: First Results from the Moon Mineralogy Mapper (M3)

India's Chandrayaan-1 successfully launched October 22, 2008 and went into lunar orbit a few weeks later. Commissioning of instruments began in late November and was near complete by the end of the year. Initial data for NASA's Moon Mineralogy Mapper (M3) were acquired across the Orientale Basin and the science results are discussed here. M 3 image-cube data provide mineralogy of the surface in geologic context. A major new result is that the existence and distribution of massive amounts of anorthosite as a continuous stratigraphic crustal layer is now irrefutable