Rocky Material Research Articles

Making the Planetary Material Diversity during the Early Assembling of the Solar System

Abstract Chondritic meteorites, the building blocks of terrestrial planets, are made of an out-of-equilibrium assemblage of solids formed at high and low temperatures, either in our Solar system or previous generations of stars. For decades this was considered to result from large-scale transport processes in the Sun’s isolated accretion disk. However, mounting evidence suggests that refractory inclusions in chondrites formed contemporaneously with the disk building. Here we numerically investigate, using a 1D model and several physical and chemical processes, the formation and transport of rocky materials during the collapse of the Sun’s parent cloud and the consequent assembling of the Solar Nebula. The interplay between the cloud collapse, the dynamics of gas and dust, vaporization, recondensation, and thermal processing of different species in the disk results in a local mixing of solids with different thermal histories. Moreover, our results also explain the overabundance of refractory materials far from the Sun and their short-formation timescales, during the first tens of kyr of the Sun, corresponding to class 0-I, opening new windows into the origin of the compositional diversity of chondrites.

Implications of Captured Interstellar Objects for Panspermia and Extraterrestrial Life

Abstract We estimate the capture rate of interstellar objects by means of three-body gravitational interactions. We apply this model to the Sun–Jupiter system and the Alpha Centauri A&B binary system, and find that the radius of the largest captured object is a few tens of km and Earth-sized, respectively. We explore the implications of our model for the transfer of life by means of rocky material. The interstellar comets captured by the “fishing net” of the solar system can be potentially distinguished by their differing orbital trajectories and ratios of oxygen isotopes through high-resolution spectroscopy of water vapor in their tails.

The first 200 kyr of the Solar System: making the planetary material diversity

AbstractChondrites are made of a mixture of solids formed at high and low temperatures. This heterogeneity was thought to be produced by large scale transport processes in the Sun’s isolated accretion disk. However, mounting evidences suggest that refractory inclusions in chondrites were produced together with the disk formation.We present numerical simulations of the formation and transport of rocky materials during the collapse of the Solar Nebula’s parent cloud and the consequent disk assembling.We find that the interplay between the cloud collapse, the dynamics of gas and dust and thermal processing of different species in the disk, results in a local mixing of solids with different thermal histories. Our simulations return an heterogeneous distribution of refractory material with higher concentration in the outer disk. This refractory material has a short formation timescales, during the first tens of kyr of the Sun (class 0-I). Our results open new frontiers into the origin of the compositional diversity of chondrites.

An asteroseismic view of the radius valley: stripped cores, not born rocky

Various theoretical models treating the effect of stellar irradiation on planetary envelopes predict the presence of a radius valley: i.e. a bimodal distribution of planet radii, with super-Earths and sub-Neptune planets separated by a valley at around $\approx 2~R_\oplus$. Such a valley was observed recently, owing to an improvement in the precision of stellar, and therefore planetary radii. Here we investigate the presence, location and shape of such a valley using a small sample with highly accurate stellar parameters determined from asteroseismology, which includes 117 planets with a median uncertainty on the radius of 3.3%. We detect a clear bimodal distribution, with super-Earths ($\approx 1.5~R_\oplus$) and sub-Neptunes ($\approx 2.5~R_\oplus$) separated by a deficiency around $2~R_\oplus$. We furthermore characterize the slope of the valley as a power law $R \propto P^\gamma$ with $\gamma = {-0.09^{+0.02}_{-0.04}}$. A negative slope is consistent with models of photo-evaporation, but not with the late formation of rocky planets in a gas-poor environment, which would lead to a slope of opposite sign. The exact location of the gap further points to planet cores consisting of a significant fraction of rocky material.

Interior structure models and fluid Love numbers of exoplanets in the super-Earth regime

Space missions such as CoRoT and Kepler have made the transit method the most successful technique in observing extrasolar planets. However, although the mean density of a planet can be derived from its measured mass and radius, no details about its interior structure, such as the density profile, can be inferred so far. If determined precisely enough, the shape of the transiting light curve might, in principle, reveal the shape of the planet, and in particular, its deviation from spherical symmetry. These deformations are caused, for instance, by the tidal interactions of the planet with the host star and by other planets that might orbit in the planetary system. The deformations depend on the interior structure of the planet and its composition and can be parameterized as Love numbers kn. This means that the diversity of possible interior models for extrasolar planets might be confined by measuring this quantity. We present results of a wide-ranging parameter study in planet mass, surface temperature, and layer mass fractions on such models for super-Earths and their corresponding Love numbers. Based on these data, we find that k2 is most useful in assessing the ratio of rocky material to iron and in ruling out certain compositional configurations for measured mass and radius values, such as a prominent core consisting of rocky material. Furthermore, we apply the procedure to exoplanets K2-3b and c and predict that K2-3c probably has a thick outer water layer.

The chemical composition of α Centauri AB revisited

The two solar-like stars α Cen A and B have long served as cornerstones for stellar physics in virtue of their immediate proximity, association in a visual binary, and masses that bracket that of the Sun. The recent detection of a terrestrial planet in the cool, suspected tertiary Proxima Cen now makes the system also of prime interest in the context of planetary studies. It is therefore of fundamental importance to tightly constrain the properties of the individual stellar components. We present a fully self-consistent, line-by-line differential abundance analysis of α Cen AB based on high-quality HARPS data. Various line lists are used and analysis strategies implemented to improve the reliability of the results. Abundances of 21 species with a typical precision of 0.02–0.03 dex are reported. We find that the chemical composition of the two stars is not scaled solar (e.g. Na and Ni excess, depletion of neutron-capture elements), but that their patterns are strikingly similar, with a mean abundance difference (A – B) with respect to hydrogen of –0.01 ± 0.04 dex. Much of the scatter may be ascribed to physical effects that are not fully removed through a differential analysis because of the mismatch in parameters between the two components. We derive an age for the system from abundance indicators (e.g. [Y/Mg] and [Y/Al]) that is slightly larger than solar and in agreement with most asteroseismic results. Assuming coeval formation for the three components belonging to the system, this implies an age of about ~6 Gyrs for the M dwarf hosting the terrestrial planet Proxima Cen b. After correction for Galactic chemical evolution effects, we find a trend between the abundance ratios and condensation temperature in α Cen A akin to that of the Sun. However, taking this finding as evidence for the sequestration of rocky material locked up in planets may be premature given that a clear link between the two phenomena remains to be established. The similarity between the abundance pattern of the binary components argues against the swallowing of a massive planet by one of the stars after the convective zones have shrunk to their present-day sizes.

Assessment of the ecological efficiency of the open development of non-metallic deposits of useful minerals

The object of research is the environmental safety of the functioning of mining enterprises. One of the most problematic places there are significant differences in the mining and geological conditions and geometrical parameters of the quarries, the type and technical condition of the mining and transportation equipment used in mining enterprises, as well as the need to refine reserves in a reduced sanitary protection zone. Changes in the procedure for assessing the environmental impact of a planned activity by mining enterprises should include the development and implementation of additional technological solutions that will help reduce pollution in the adjacent territories. Therefore, there is a need to develop standardized approaches, the use of which will allow analyzing the technological processes of mining enterprises and be more dangerous from an environmental point of view, where significant amounts of pollutant emissions are generated.In the course of the study, three typical technological schemes for the development of deposits of rocky building materials, differing in productivity and emissions of pollutants to adjacent territories, have been analyzed. It has been established that the use of belt conveyors allows reducing the zone of influence of an enterprise on the ecological state of adjacent territories and minimizing the environmental risks of the functioning of mining enterprises.For the localization of emissions of pollutants in the mining enterprise, it is reasonable to place mobile and portative crushing and screening plants in a quarry directly in the faces or at work sites. This will reduce environmental pollution levels and increase the comfort of living in the mining regions.Thanks to the use of modern research methods, methods of cartographic modeling and scientific forecasting and the use of computer programs, optimal environmental-friendly field development technologies have been developed. Their use will reduce emissions of pollutants outside the sanitary protection zone and improve the environmental image of the mining enterprise. Such approaches will contribute to the successful passage of the environmental audit of mining enterprises, obtaining international environmental certificates and the development of new markets for products.

Ejection of rocky and icy material from binary star systems: implications for the origin and composition of 1I/‘Oumuamua

Abstract In single-star systems like our own Solar system, comets dominate the mass budget of bodies ejected into interstellar space, since they form further away and are less tightly bound. However, 1I/‘Oumuamua, the first interstellar object detected, appears asteroidal in its spectra and lack of detectable activity. We argue that the galactic budget of interstellar objects like 1I/‘Oumuamua should be dominated by planetesimal material ejected during planet formation in circumbinary systems, rather than in single-star systems or widely separated binaries. We further show that in circumbinary systems, rocky bodies should be ejected in comparable numbers to icy ones. This suggests that a substantial fraction of interstellar objects discovered in future should display an active coma. We find that the rocky population, of which 1I/‘Oumuamua seems to be a member, should be predominantly sourced from A-type and late B-star binaries.

Kronos and Krios: Evidence for Accretion of a Massive, Rocky Planetary System in a Comoving Pair of Solar-type Stars

Abstract We report and discuss the discovery of a significant difference in the chemical abundances of a comoving pair of bright solar-type stars, HD 240430 and HD 240429. The two stars have an estimated 3D separation of ≈0.6 pc (≈0.01 pc projected) at a distance of r ≈ 100 pc with nearly identical 3D velocities, as inferred from Gaia TGAS parallaxes and proper motions, and high-precision radial velocity measurements. Stellar parameters determined from high-resolution spectra obtained with the High Resolution Echelle Spectrometer (HIRES) at the Keck Observatory indicate that the two stars are ∼4 Gyr old. The more metal-rich of the two, HD 240430, shows an enhancement of refractory ( K) elements by ≈0.2 dex and a marginal enhancement of (moderately) volatile elements ( K; , , , , and ). This is the largest metallicity difference found in a wide binary pair to date. Additionally, HD 240430 shows an anomalously high surface lithium abundance ( ), higher than its cooler companion by 0.5 dex. The proximity in phase-space and ages between the two stars suggests that they formed together with the same composition, which is at odds with the observed differences in metallicity and abundance patterns. We therefore suggest that the star HD 240430, “Kronos,” accreted of rocky material after birth, selectively enhancing the refractory elements as well as lithium in its surface and convective envelope.

Deep Blue Geomediations: Following Lapis Lazuli in Three Ecological Assemblages

Deep Blue Geomediations:Following Lapis Lazuli in Three Ecological Assemblages Patricia Pisters (bio) Stones, like us, stand at the intersection of countless lines crossing one another and receding to infinity, at the center of a field of forces too unpredictable to be measured… (Yourcenar xix) Mining the Blue Mountain: Matter-Flow of the Machinic Phylum On my desk, next to my laptop, a small piece of lapis lazuli. My eye is captured by the intense blue from its most important component, the mineral lazurite. The stone also contains white calcite specks and some metallic glistering from its pyrite elements. Looking at the play of colors, feeling the weight and the surface of the rocky material, I am reminded of Marguerite Yourcenar's words at the end of her introduction to Caillois's The Writing of Stones when she invokes stones as force fields "at the intersection of countless lines crossing one another" (Yourcenar xix). And I wonder, what are the force fields and intersecting lines "receding to infinity" contained in this small piece of earthly material? How has this ultramarine blue become "the most perfect of all colors" (Cennini 36), as described by Cennini in his famous The Craftman's Handbook of the late Middle Ages? How has lapis lazuli traveled in the world, as an aesthetic object, as a perfect pigment for the most beautiful blue, but also been implicated in economic and political forces? What kind of "geomediations" traverse this deep blue stone? And if all these forces are too unpredictable to measure, as Yourcenar contended, is there another way to uncover some of the complex entanglements of the material and immaterial dimensions of this particular aspect of the lithosphere? A good starting place might be the Blue Mountain (Koh-e-Laguard) of the Sar-e-Sang mines in East Afghanistan where since 6,000 BC the best quality lapis lazuli has been extracted from the earth. In 2009, artist Pieter Paul Pothoven traveled to Afghanistan in search for the Sar-e-Sang mines.1 Intrigued by the extreme stability of the rocky [End Page 36] material in an extremely unstable environment (Afghanistan is a contested and mediated area in geopolitics, as will be discussed below), Pothoven started his investigations by traversing the inhospitable landscape of the Hindu Kush Mountains in Badakhshan, reaching the mines after an arduous journey. He was able to buy some of the stones from the local miners and, since then, has made a series of ongoing art works that invoke both the material and spiritual qualities of the stone and question the geophysical and political dimensions of art history and contemporary media culture. These works will be my guides in uncovering some of the hidden dimensions of the blue stone. Other guidelines are offered by new materialist philosophy that acknowledges the profound connections between the human and nonhuman, inspired by the work of Deleuze and Guattari.2 In A Thousand Plateaus, Deleuze and Guattari discuss mining in connection to metallurgy, miners and smiths being the first metallurgists that know how to follow and transform the forces of matter (404–415). While their remarks are mostly related to metal, Deleuze and Guattari indicate that also wood, clay, stones and minerals can be taken into account when they argue that metallurgy is not an exact science that discovers universal stable laws, since metallurgy is inseparable from several lines of variation: according to different qualities of the material itself (quality of the ore, varieties of the stones) and according to different processes of transformation (washing, polishing, grinding, mixing with wax and gum, heating, etc.). These variables make the materials both of singular order (each piece of rock is different), and according to its transformation processes, expressive of different levels of affective qualities. Deleuze and Guattari introduce the concept of a "machinic phylum," which they define as "materiality, natural or artificial, and both simultaneously; it is matter in movement, in flux, in variation, matter as a conveyor of singularities and traits of expression" (409). Because of its constant flow and variation, the machinic phylum is very hard to measure indeed. Therefore, Deleuze and Guattari argue that the "matter-flow can only be followed" (409).3 So let...

Exploration of potential groundwater resources at Thuwal area, north of Jeddah, Saudi Arabia, using remote sensing data analysis and geophysical survey

The study uses the applications of remote sensing in analyzing the main topographic features of the study area. The digital elevation model derived from the Shuttle Radar Topography Mission (SRTM) satellite is used to devise spillway torrents and their tributaries of the different drainage basins in the study area. The digital rainfall data recorded by the Tropical Rainfall Measuring Mission (TRMM) climate research satellite is used to determine places with the highest rainfall within the different drainage basins in the area. Other satellite data (e.g. Landsat-8) are used in identifying and studying the various geological structures in the study area, which intersect the spillway torrents. Such areas may allow seizure of large quantities of water as potential, close to the surface, groundwater (Quaternary) aquifer. Areas of potential hydrological traps have been identified and marked for further geophysical (geoelectrical) surveys. The geophysical studies helped in identifying the shallow geological structures and the thickness of the subsurface sediments. It also assists in determining the size of the groundwater aquifer and the water quality within these aquifers. The study showed a decline of freshwater aquifer in Quaternary sediments. The Tertiary groundwater aquifer is the most prevalent, where this appears normal saline aquifer. All the aquifers within the study area are being recharged from Quaternary sediments by rainwater. The cumulative annual precipitation rate increases in the South-East of the study area, specifically over Wadi Khulais and significantly drops to lower rainfall rates in the rest of the region. Running water permeates the Quaternary sediments, which in turn infiltrates and recharges the Tertiary aquifer. The salinity of the latter depends mostly on the nature of its constituent rocky material.

Humusica 2, article 16: Techno humus systems and recycling of waste

Techno humus systems correspond to man-made topsoils under prominent man influence. They may be purposely conceived for supporting agricultural activities or dumping of waste products, sometimes abandoned to an unknown evolution. Both categories needed a more scientific frame. This is the reason we classified them as morpho-functional humus systems. Improving agricultural soils with organic waste products is an ancestral practice. We present four examples of techno humus systems purposely created for supporting plant growth. Considering a simple home-made composting pile, we give a few basic notions about the biological functioning of these artificial humus systems. Humipedon functioning and structuration are similar to those observed in natural humus systems. Using even animal manure, we illustrate how to manage larger compost piles of waste for application in farming areas. Composting waste that contains animal proteins needs a more careful measurement of the temperature of the pile and a longer period of elevated temperature in the core of the pile. Mulching of pruning residues is presented in a large urban context. The use of mulch must take into account quality and composition of woody material. The lack of nutrients in some residues has to be compensated by a moderate use of appropriate mineral fertilizers. Municipal solid waste, anaerobic digestion residues (grape remains) and spent mushroom compost, eventually mixed with mineral fertilizers, have been tested in horticulture. Benefits and drawbacks are listed for each experiment, with the evolution of carbon storage along 8 years of horticultural practice. Finally, we present an example of “dump” humus system. Mine tailing wastes represent a huge problem in many countries. Pointing on their microbial activity, we show that they must be seen as manageable living humipedons, not as piles of inert rocky material.

Modeling concentric crater fill in Utopia Planitia, Mars, with an ice flow line model

Impact craters in the mid-latitudes of Mars are commonly filled to variable degrees with some combination of ice, dust, and rocky debris. Concentric surface features visible in these craters have been linked to debris transportation and glacial and periglacial processes. Concentric crater fill (CCF) observed today are interpreted to be the remains of repeated periods of accumulation and sublimation during the last tens to hundreds of million years. Previous work suggests that during phases of high obliquity, ice accumulates in crater interiors and begins to flow down steep crater slopes, slowly filling the crater. During times of low obliquity ice is protected from sublimation through a surface debris layer consisting of dust and rocky material. Here, we use an ice flow line model to understand the development of concentric crater fill.In a regional study of Utopia Planitia craters, we address questions about the influence of crater size on the CCF formation process, the time scales needed to fill an impact crater with ice, and explore commonly described flow features of CCF. We show that observed surface debris deposits as well as asymmetric flow features can be reproduced with the model. Using surface mass balance data from global climate models and a credible obliquity scenario, we find that craters less than 80 km in diameter can be entirely filled in less than 8 My, beginning as recently as 40 Ma ago. Uncertainties in input variables related to ice viscosity do not change the overall behavior of ice flow and the filling process. We model CCF for the Utopia Planitia region and find subtle trends for crater size versus fill level, crater size versus sublimation reduction by the surface debris layer, and crater floor elevation versus fill level.

Lithium abundance and6Li/7Li ratio in the active giant HD 123351

Current three-dimensional (3D) hydrodynamical model atmospheres together with NLTE spectrum synthesis, permit to derive reliable atomic and isotopic chemical abundances from high-resolution stellar spectra. Not much is known about the presence of the fragile 6Li isotope in evolved solar-metallicity RGB stars, not to mention its production in magnetically active targets like HD123351. From fits of the observed CFHT spectrum with synthetic line profiles based on 1D and 3D model atmospheres, we seek to estimate the abundance of the 6Li isotope and to place constraints on its origin. We derive A(Li) and the 6Li/7Li isotopic ratio by fitting different synthetic spectra to the Li-line region of a high-resolution CFHT spectrum (R=120 000, S/R=400). The synthetic spectra are computed with four different line lists, using in parallel 3D hydrodynamical CO5BOLD and 1D LHD model atmospheres and treating the line formation of the lithium components in non-LTE (NLTE). We find A(Li)=1.69+/-0.11 dex and 6Li/7Li=8.0+/-4.4 % in 3D-NLTE, using the line list of Mel\'endez et al. (2012), updated with new atomic data for V I, which results in the best fit of the lithium line profile of HD123351. Two other line lists lead to similar results but with inferior fit qualities. Our 2-sigma detection of the 6Li isotope is the result of a careful statistical analysis and the visual inspection of each achieved fit. Since the presence of a significant amount of 6Li in the atmosphere of a cool evolved star is not expected in the framework of standard stellar evolution theory, non-standard, external lithium production mechanisms, possibly related to stellar activity or a recent accretion of rocky material, need to be invoked to explain the detection of 6Li in HD123351.

Earth’s thermal evolution, mantle convection, and Hadean onset of plate tectonics

During Solar System condensation, the early Earth formed through planetesimal accretion, including collision of a Mars-sized asteroid. These processes rapidly increased the overall thermal budget and partial fusion of the planet. Aided by heat supplied by radioactivity and infall of the Fe-Ni core, devolatilization and chemical-density stratification attended planetary growth. After the thermal maximum at ∼4.4Ga, terrestrial temperatures gradually declined as an early Hadean magma ocean solidified. By ∼4.3–4.2Ga, H2O oceans+a dense CO2-rich atmosphere blanketed the terrestrial surface. Near-surface temperatures had fallen well below the low-P solidi of dry peridotite, basalt, and granite, ∼1300, ∼1120, and ∼950°C, respectively. At less than half their melting T, rocky materials existed as thin lithospheric platelets in the surficial Hadean Earth. Upper mantle stagnant-lid convection may have operated locally, but was rapidly overwhelmed by heat build-up-induced asthenospheric circulation, rifting and subduction, because massive heat transfer required vigorous mantle overturn in the early, hot planet. Bottom-up mantle overturn, involving abundant plume ascent, brought deep-seated heat to the surface. It decreased over time as cooling, plate enlargement, and top-down plate descent increased. Thickening, lateral extension, and contraction typified the post-Hadean lithosphere. Geologic evolutionary stages included: (a) ∼4.5–4.4Ga, the magma ocean solidified, generating ephemeral, ductile platelets; (b) ∼4.4–2.7Ga, small oceanic and continental plates were produced, then were destroyed by mantle return flow before ∼4.0Ga; eventually, continental material began to accumulate as largely subsea, sialic crust-capped lithospheric collages; (c) ∼2.7–1.0Ga, progressive suturing of old shields and younger orogenic belts led to cratonal plates typified by emerging continental freeboard, intense sedimentary differentiation, and episodic glaciation during transpolar plate drift; temporally limited stagnant-lid mantle convection occurred beneath growing supercontinents; (d) ∼1.0Ga-present, laminar-flowing mantle cells are capped by giant, stately moving plates. Near-restriction of komatiitic lavas to the Archean, and formation of multicycle sediments, ophiolite complexes±alkaline igneous rocks, and high-pressure/ultrahigh-pressure (HP/UHP) metamorphic belts in youngest Proterozoic and Phanerozoic orogens reflect increasing density of cool oceanic plates, but decreasing subductability of enlarging, more buoyant continental plates. Attending assembly of supercontinents, negative buoyancy of thickening oceanic lithosphere began to control the overturn of suboceanic mantle as cold, top-down convection. The scales and dynamics of hot asthenospheric upwelling versus plate foundering and mantle return flow (bottom-up plume ascent versus top-down plate subduction) evolved gradually, due to planetary cooling. After accretion of the Earth, heat transfer through mantle convection has resulted in the existence of surficial rocky plates or platelets, and vigorous, lithosphere-coupled mantle overturn since ∼4.4Ga. Thus plate-tectonic processes have typified the Earth’s thermal history since Hadean time.

Historic scale and persistence of drill cuttings impacts on North Sea benthos

Despite its long history of hydrocarbon exploitation, the United Kingdom lacks scientific protocols to monitor ecological impacts of drill cuttings (mixtures between rocky material excavated from wells and drilling mud). The present study used the UK Benthos industry database to apply standardised variance partitioning and measure the scale and persistence of these effects at 19 sites across the UK sector of the North Sea. Generally, effects were limited to within 1 km from the platform, but two platforms historically drilled with oil-based mud were impacted up to 1.2 km away. Impacts persisted for at least 6–8 years in the northern and central North Sea, but were undetectable in the south where cuttings piles do not accumulate. This study underpins new recommendations to implement regional, phase-based approaches to drill cuttings monitoring, and to apply a precautionary approach in considering decommissioning options that will minimise disturbance to cuttings piles.

Vegetation establishment on ‘Green Walls’: Integrating shotcrete walls from road construction into the landscape

The establishment of a sustainable vegetation layer on shotcrete walls subjected to road environment represents enormous challenges. High inclination of almost 90°, the exposed position of the walls near streets as well as lack of soil and water supply pose major limiting conditions. The objective of this study was to evaluate the performance of an innovative greening technology for vertical structures in terms of vegetation development on varying plant substrates and geotextiles.The field experiment included testing three plant substrates on basis of nearby rocky excavation material (‘Innsbrucker Quarzphyllit’, ‘Bündnerschiefer’ and ‘Zentralgneis’) combined with compost. Additionally, five geotextiles (geogrid (3x4 mm), geogrid (9x10 mm), coir net, coir mat, geo mat) were applied for assessment. All test combinations were evaluated regarding vegetation cover, species composition, and biomass production from 2015 to 2016. Analyses of chemical properties were conducted for all plant substrates.Results showed highest vegetation cover ratio on ‘Bündnerschiefer’ and ‘Innsbrucker Quarzphyllit’, which can be explained by the favorable mineral composition (nutrient storage capacity) and chemical properties of compost (lower values of electrical conductivity and C/N ratio).In conclusion, the use of ‘Green Walls’ filled with ‘Bündnerschiefer’ or ‘Innsbrucker Quarzphyllit’ plant substrate in combination with netlike geotextiles like geogrid or coir net proved best. They are promising in terms of establishing an optimal vegetation cover on vertical structures and are well suited for integrating shotcrete walls into the landscape. The use of local excavation material for greening purposes thus can be confirmed. Though, the use of high-quality compost is crucial.

Comparative analysis of asphalt concrete mixtures employing pebbles and synthetic coarse aggregate of calcined clay in the Amazon region

ABSTRACTSeveral parts of the Amazon region present high costs concerning to pavement services, mainly because of their geological condition where there is a lack of rocky material. In these areas, natural pebble deposits or stone quarries are very distant from the consumption locations. The frequently used coarse aggregate in the State of Amazonas, Brazil, is the pebble taken from the riverbeds, with an at least 500 km distance from the greatest consumption centre, resulting in a high transportation fee which approaches in about 50% of the final product cost. Searching for an alternative and non-conventional material which could replace the pebbles, the natural clay was studied due to its mineral abundance in the Amazon region. The production process adopted by the ceramic industry was reproduced in laboratory tests, in a handcrafted way, using a manual mill composed by four nozzles with dimensions of 12.7, 9.5, 4.8 and 2.0 mm. The wet aggregates were calcinated at temperatures of 780, 850, 950, 1050 and 1150 °C, and physically characterised. It was made a comparative analysis between the conventional hot mixed asphalt concrete (with pebbles) and using synthetic aggregates, studying several physical and mechanical parameters. Asphalt mixtures made with synthetic aggregates offered better bonding between their components when compared with those made with pebbles, favouring gain in mechanical resistance, since they represented a structural skeleton more resistant than pebbles. In addition, as the firing temperature of the synthetic aggregates increased, the consumption of asphalt cement decreased, due to the phase transformations of the crystal to the amorphous phase. The results of the resilient modulus to static indirect tensile strength ratios allowed to infer that asphalt mixtures made with synthetic aggregates point to a longer fatigue life when compared to the pebble mixture principally at values lower than 3500.

Discovery of MgTiSi2O7: a new high-pressure silicate with the weberite structure synthesized at transition-zone conditions

The crystal structure and chemical composition of a crystal of MgTiSi2O7 synthesized in the model system MgTiO3–MgSiO3 at 15 GPa and 1600 °C have been investigated. The compound was found to crystallize with the weberite-3T structure type, space group P3121, with lattice parameters a = 6.3351(7), c = 16.325(2) A, V = 567.4(1) A3, and Z = 6. The structure was refined to R1 = 0.059 using 2092 independent reflections, and can be described as a sequence of pairs of polyhedral layers (M and N) stacked along [001]. As far as the cation sites are concerned, M and N layers have general formula AB3 and A3B, respectively, where B are the octahedrally coordinated cations (B1, B2, and B3), which mainly accommodate Si. The octahedral framework gives rise to three types of larger cavities occupied by eight-coordinated Mg (A1), Ti (A2), and mixed (Mg,Ti) (A3) atoms. Electron microprobe analysis gave the Mg0.99Si1.62Ti1.39O7 stoichiometry for the studied phase. The successful synthesis of this phase demonstrates that titanium can stabilize heretofore unknown Mg–Si-oxides, the major Earth and rocky planet-forming materials, and can provide new constraints on thermobarometry of wadsleyite/ringwoodite, and garnet-bearing assemblages.

PLANETARY ENGULFMENT AS A TRIGGER FOR WHITE DWARF POLLUTION

ABSTRACT The presence of a planetary system can shield a planetesimal disk from the secular gravitational perturbations due to distant outer massive objects (planets or stellar companions). As the host star evolves off the main sequence to become a white dwarf, these planets can be engulfed during the giant phase, triggering secular instabilities and leading to the tidal disruptions of small rocky bodies. These disrupted bodies can feed the white dwarfs with rocky material and possibly explain the high-metallicity material in their atmospheres. We illustrate how this mechanism can operate when the gravitational perturbations are due to the KL mechanism from a stellar binary companion, a process that is activated only after the planet has been removed/engulfed. We show that this mechanism can explain the observed accretion rates if: (1) the planetary engulfment happens rapidly compared to the secular timescale, which is generally the case for wide binaries ( au) and planetary engulfment during the asymptotic giant branch; (2) the planetesimal disk has a total mass of . We show that this new mechanism can provide a steady supply of material throughout the entire life of the white dwarfs for all cooling ages and can account for a large fraction (up to nearly half) of the observed polluted white dwarfs.