Carbonates in CM chondrites: Complex formational histories and comparison to carbonates in CI chondrites

Abstract– CM chondrites are primitive solar‐system materials that have undergone high degrees of aqueous alteration, resulting in the formation of secondary minerals including carbonates. Two different carbonate minerals (calcite/aragonite and dolomite) together constitute 1.4–2.8 vol% of CM chondrites. In contrast, CI chondrites contain four different carbonate minerals: calcite/aragonite, dolomite, breunnerite, and siderite. CI chondrites have abundant dolomite, a mineral that seems to be absent in the most aqueously altered CM chondrites. In this study, carbonates in seven CM chondrites (Y‐791198, LaPaz Icefield 04796, Cold Bokkeveld, Nogoya, Queen Alexandra Range 93005, Allan Hills 83100, and Meteorite Hills 01070) were studied petrographically and by electron microprobe. The results indicate that carbonate formation in CM chondrites differs from that in CI chondrites and is more complex than previously recognized. Our studies of CM chondrites indicate that (1) carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition, (2) at some stage, Ca and Mg activities in the environment were high enough to form metastable dolomite, and (3) dolomites disappeared in the most aqueously altered CM chondrites.     

Trails of solar system minor bodies on WFC/ACS images

In this paper, we analyse very short arcs of minor bodies of the Solar System detected on Hubble Space Telescope (HST) Wide Field Channel ACS images. In particular, we address how to constrain the Keplerian orbital elements for minor body detections, illustrating the method for two objects. One of the minor bodies left 13 successive trails, making it the most well-sampled object yet identified in the HST archive. Most interestingly, we also address the problem of ephemeris prediction and show that in the particular case of HST very short arcs the confinement window for subsequent recovery is significantly reduced to a narrow linear region, that would facilitate successive observations.     

What can we learn from Neutron Star X-Ray Binaries' JETS?

We review our current knowledge of the disk-jet coupling in neutron star X-ray binaries. We compare neutron star and black hole X-ray binaries, by means of radio and X-ray observations, in order to understand the role played in the production of the jet, by characteristics proper of the accreting compact object involved: the existence of a solid surface, the presence of an ergosphere/event horizon, the strength of the magnetic field, the spin of the compact object.     

The intrinsic fraction of broad-absorption line quasars

We carefully reconsider the problem of classifying broad-absorption line quasars (BALQSOs) and derive a new, unbiased estimate of the intrinsic BALQSO fraction from the Sloan Digital Sky Survey (SDSS) DR3 quasi-stellar object (QSO) catalogue. We first show that the distribution of objects selected by the so-called 'absorption index' (AI) is clearly bimodal in log AI, with only one mode corresponding to definite BALQSOs. The surprisingly high BALQSO fractions that have recently been inferred from AI-based samples are therefore likely to be overestimated. We then present two new approaches to the classification problem that are designed to be more robust than the AI, but also more complete than the traditional 'balnicity index' (BI). Both approaches yield observed BALQSO fractions around 13.5 per cent, while a conservative third approach suggests an upper limit of 18.3 per cent. Finally, we discuss the selection biases that affect our observed BALQSO fraction. After correcting for these biases, we arrive at our final estimate of the intrinsic BALQSO fraction. This is   f _BALQSO= 0.17 ± 0.01 (stat) ± 0.03 (sys)  with an upper limit of   f _BALQSO≃ 0.23  . We conclude by pointing out that the bimodality of the log AI distribution may be evidence that the BAL-forming region has clearly delineated physical boundaries.     

Global variations in regolith properties on asteroid Vesta from Dawn's low‐altitude mapping orbit

We investigate the depth, variability, and history of regolith on asteroid Vesta using data from the Dawn spacecraft. High‐resolution (15–20 m pixel^?1) Framing Camera images are used to assess the presence of morphologic indicators of a shallow regolith, including the presence of blocks in crater ejecta, spur‐and‐gully–type features in crater walls, and the retention of small (<300 m) impact craters. Such features reveal that the broad, regional heterogeneities observed on Vesta in terms of albedo and surface composition extend to the physical properties of the upper ~1 km of the surface. Regions of thin regolith are found within the Rheasilvia basin and at equatorial latitudes from ~0–90°E and ~260–360°E. Craters in these areas that appear to excavate material from beneath the regolith have more diogenitic (Rheasilvia, 0–90°E) and cumulate eucrite (260–360°E) compositions. A region of especially thick regolith, where depths generally exceed 1 km, is found from ~100–240°E and corresponds to heavily cratered, low‐albedo surface with a basaltic eucrite composition enriched in carbonaceous chondrite material. The presence of a thick regolith in this area supports the idea that this is an ancient terrain that has accumulated a larger component of exogenic debris. We find evidence for the gardening of crater ejecta toward more howarditic compositions, consistent with regolith mixing being the dominant form of “weathering” on Vesta.     

Integrated use of archival aerial photogrammetry,GNSS, and InSAR data for the monitoring of the Patigno landslide (Northern Apennines,Italy)

Landslides - The morphological changes of unstable areas can be identified using different methodologies that allow repeated surveys over time. The integration between the data obtained from...     

Validation of Geant4 10.3 simulation of proton interaction for space radiation effects

Monte Carlo simulation of space radiation effects induced by protons is important for design of space missions. Geant4 is a well established toolkit for Monte Carlo simulation focused on high energy physics applications. In this work, a set of new validation results versus data for Geant4 electromagnetic and hadronic interaction of protons is presented and discussed. Optimal configuration of Geant4 physics for space applications is proposed.     

Additive effects of climate change and human hunting explain population decline and extinction in cave bears

Cave bears (Ursus spelaeus) are an iconic component of the European late Quaternary Ice Age megafauna. Recent demographic analyses based on cave bear mtDNA sequences and refined radiocarbon dating indicate that cave bear population size and genetic diversity started to decline some 50 kilo years ago (kya). Hence, neither the coldest phase of the last glaciation (started some 24 kya), nor the colonization of Europe by Palaeolithic hunters (started some 45 kya) coincides with the beginning of population decline. Here, we reconstructed cave bear climatic niche evolution through time. Then, we performed spatially explicit population viability analyses to assess cave bear demographics through time in response to climatic changes, human effects on bear survival and their combination. We found that climate change was responsible for a 10‐fold decrease in cave bear population size after 40 kya. However, climate change on its own could not explain U. spelaeus extinction at 24 kya. Additional negative effects consistent with human population expansion are required to explain both U. spelaeus' retreat from eastern Europe since 40 kya and its final extinction.     

The cross-correlation between galaxies and groups: probing the galaxy distribution in and around dark matter haloes

Some massive binaries should contain energetic pulsars which inject relativistic leptons from their inner magnetospheres and/or pulsar wind regions. If the binary system is compact enough, then these leptons can initiate inverse Compton (IC) e^± pair cascades in the anisotropic radiation field of a massive star. γ-rays can be produced in the IC cascade during its development in a pulsar wind region and above a shock in a massive star wind region where the propagation of leptons is determined by the structure of a magnetic field around the massive star. For a binary system with specific parameters, we calculate phase-dependent spectra and fluxes of γ-rays escaping as a function of the inclination angle of the system and for different assumptions on injection conditions of the primary leptons (their initial spectra and location of the shock inside the binary). We conclude that the features of γ-ray emission from such massive binaries containing energetic pulsars should allow us to obtain important information on the acceleration of particles by the pulsars, and on interactions of a compact object with the massive star wind. Predicted γ-ray light curves and spectra in the GeV and TeV energy ranges from such binary systems within our Galaxy and Magellanic Clouds should be observed by future AGILE and GLAST satellites and low-threshold Cherenkov telescopes, such as MAGIC, HESS, VERITAS or CANGAROO III.     

Channelization of a large Alpine river: what is left of its original morphodynamics?

The Adige River drains 12 200 km² of the Eastern Alps and flows for 213 km within this mountain range. Similar to other large rivers in Central Europe, the Adige River was subject to massive channelization works during the 19th century. Thanks to the availability of several historical maps, this river represents a very valuable case study to document the extent to which the morphology of the river changed due to channelization and to understand how much is left of its original morphodynamics. The study was based on the analysis of seven sets of historical maps dating from 1803–1805 to 1915–1927, on geomorphological analysis, on the application of mathematical morphodynamic theories and on the application of bar and channel pattern prediction models. The study concerns 115 km of the main stem and 29 km of its tributaries. In the pre‐channelization conditions, the Adige River presented a prevalence of single‐thread channel planforms. Multi‐thread patterns developed only immediately downstream of the main confluences. During the 19th century, the Adige underwent considerable channel adjustment, consisting of channel narrowing, straightening, and reduction of bars and islands. Multi‐thread and single‐thread reaches evolved through different evolutionary trajectories, considering both the channel width and the bar/vegetation interaction. Bar and channel pattern predictors showed good correspondence with the observed patterns, including the development of multi‐thread morphologies downstream of the confluences. Application of the free‐bar predictor helped to interpret the strong reduction – almost complete loss – of exposed sediment bars after the channelization works, quantifying the riverbed inclination to form alternate bars. This morphological evolution can be observed in other Alpine rivers of similar size and similar massive channelization, therefore, a simplified conceptual model for large rivers subjected to channelization is proposed, showing that a relatively small difference in the engineered channel width may have a strong impact on the river dynamics, specifically on bar formation. Copyright © 2017 John Wiley & Sons, Ltd.