High Survivability of Micrometeorites on Mars: Sites With Enhanced Availability of Limiting Nutrients

NASA's strategy in exploring Mars has been to follow the water, because water is essential for life, and it has been found that there are many locations where there was once liquid water on the surface. Now perhaps, to narrow down the search for life on a barren basalt‐dominated surface, there needs to be a refocusing to a strategy of “follow the nutrients.” Here we model the entry of metallic micrometeoroids through the Martian atmosphere, and investigate variations in micrometeorite abundance at an analogue site on the Nullarbor Plain in Australia, to determine where the common limiting nutrients available in these (e.g., P, S, Fe) become concentrated on the surface of Mars. We find that dense micrometeorites are abundant in a range of desert environments, becoming concentrated by aeolian processes into specific sites that would be easily investigated by a robotic rover. Our modeling suggests that micrometeorites are currently far more abundant on the surface of Mars than on Earth, and given the far greater abundance of water and warmer conditions on Earth and thus much more active weather system, this was likely true throughout the history of Mars. Because micrometeorites contain a variety of redox sensitive minerals including FeNi alloys, sulfide and phosphide minerals, and organic compounds, the sites where these become concentrated are far more nutrient rich, and thus more compatible with chemolithotrophic life than most of the Martian surface

Microstructural characterization of natural fractures and faults in the Opalinus Clay: insights from a deep drilling campaign across central northern Switzerland

Abstract The Middle-Jurassic Opalinus Clay is the foreseen host rock for radioactive waste disposal in central northern Switzerland. An extensive drilling campaign aiming to characterize the argillaceous formation resulted in a comprehensive drill core data set. The rheologically weak Opalinus Clay is only mildly deformed compared to the over- and underlying rock units but shows a variety of natural fractures. While these structures are hydraulically indistinguishable from macroscopically non-deformed Opalinus Clay today, their analysis allows for a better understanding of the deformation behaviour in the geological past. Here, we present an overview of the different fracture and fault types recorded in the Opalinus Clay and a detailed microstructural characterization of veins—natural dilational fractures healed by secondary calcite and celestite mineralizations. Macroscopic drill core analysis revealed five different natural fracture types that encompass tension gashes of various orientations with respect to bedding and small-scale faults with displacements typically not exceeding the drill core diameter. The occurrence of different fault types generally fits well with the local tectonic setting of the different drilling sites and with respect to the neighbouring regional fault zones. The microstructural investigations of the various vein types revealed their often polyphase character. Fibrous bedding-parallel veins of presumable early age were found to be overprinted by secondary slickenfibres. The polyphase nature of fibrous bedding parallel veins and slickenfibres is supported by differing elemental compositions, pointing towards repeated fracturing and mineralization events. Direct dating of vein calcites with U–Pb was unsuccessful. Nevertheless, age constraints can be inferred from structural orientations and fault slip kinematics. Accordingly, some of the veins already formed during sediment compaction in Mesozoic times, others possibly relate to Early Cenozoic foreland uplift. The youngest veins are most likely related to Late Cenozoic regional tectonic events, such as the Jura fold-and-thrust belt to the south and the Hegau-Lake Constance Graben to the northeast of the study area. During these latest tectonic events, previously formed veins acted as rheologically stiff discontinuities in the otherwise comparably weak Opalinus Clay along which deformation of the rock formation was re-localized

Recreating the OSIRIS-REx Slingshot Manoeuvre from a Network of Ground-Based Sensors

Optical tracking systems typically trade-off between astrometric precision and field-of-view. In this work, we showcase a networked approach to optical tracking using very wide field-of-view imagers that have relatively low astrometric precision on the scheduled OSIRIS-REx slingshot manoeuvre around Earth on September 22nd, 2017. As part of a trajectory designed to get OSIRIS-REx to NEO 101955 Bennu, this flyby event was viewed from 13 remote sensors spread across Australia and New Zealand to promote triangulatable observations. Each observatory in this portable network was constructed to be as lightweight and portable as possible, with hardware based off the successful design of the Desert Fireball Network. Over a 4 hour collection window, we gathered 15,439 images of the night sky in the predicted direction of the OSIRIS-REx spacecraft. Using a specially developed streak detection and orbit determination data pipeline, we detected 2,090 line-of-sight observations. Our fitted orbit was determined to be within about 10~km of orbital telemetry along the observed 109,262~km length of OSIRIS-REx trajectory, and thus demonstrating the impressive capability of a networked approach to SSA

Erratum to: Methods for evaluating medical tests and biomarkers

[This corrects the article DOI: 10.1186/s41512-016-0001-y.]

Evidence synthesis to inform model-based cost-effectiveness evaluations of diagnostic tests: a methodological systematic review of health technology assessments

Background: Evaluations of diagnostic tests are challenging because of the indirect nature of their impact on patient outcomes. Model-based health economic evaluations of tests allow different types of evidence from various sources to be incorporated and enable cost-effectiveness estimates to be made beyond the duration of available study data. To parameterize a health-economic model fully, all the ways a test impacts on patient health must be quantified, including but not limited to diagnostic test accuracy. Methods: We assessed all UK NIHR HTA reports published May 2009-July 2015. Reports were included if they evaluated a diagnostic test, included a model-based health economic evaluation and included a systematic review and meta-analysis of test accuracy. From each eligible report we extracted information on the following topics: 1) what evidence aside from test accuracy was searched for and synthesised, 2) which methods were used to synthesise test accuracy evidence and how did the results inform the economic model, 3) how/whether threshold effects were explored, 4) how the potential dependency between multiple tests in a pathway was accounted for, and 5) for evaluations of tests targeted at the primary care setting, how evidence from differing healthcare settings was incorporated. Results: The bivariate or HSROC model was implemented in 20/22 reports that met all inclusion criteria. Test accuracy data for health economic modelling was obtained from meta-analyses completely in four reports, partially in fourteen reports and not at all in four reports. Only 2/7 reports that used a quantitative test gave clear threshold recommendations. All 22 reports explored the effect of uncertainty in accuracy parameters but most of those that used multiple tests did not allow for dependence between test results. 7/22 tests were potentially suitable for primary care but the majority found limited evidence on test accuracy in primary care settings. Conclusions: The uptake of appropriate meta-analysis methods for synthesising evidence on diagnostic test accuracy in UK NIHR HTAs has improved in recent years. Future research should focus on other evidence requirements for cost-effectiveness assessment, threshold effects for quantitative tests and the impact of multiple diagnostic tests

Erratum to: Methods for evaluating medical tests and biomarkers

[This corrects the article DOI: 10.1186/s41512-016-0001-y.]

On the aggregation, differentiation and devolatilisation of volatile-rich asteroids

The development of chemically distinct parent bodies from the protoplanetary disk is controlled by the composition of their formation regions. After accretion the chemistry of planetesimals can be greatly affected by the presence of phases that can alter their oxidation state. The protoplanetary disk was stratified with respect to the volatility of elements such that in the hotter inner solar system, planets and planetesimals are composed of refractory elements, whereas those that formed further out are progressively richer in volatile elements. At about 2.6-2.8 AU, temperatures in the early solar nebula were cool enough the H₂O ice was stable, and this is known as the snowline transition. Planetesimals that formed within or beyond the snowline transition accreted with higher proportions of H₂O ice, which was later capable of driving oxidation of the silicate mineralogy through serpentinisation reactions. Thus, the planets and planetesimals that formed further from the Sun are more oxidised and more volatile rich. This thesis investigates the effect of redox processes during the aggregation, differentiation and early cooling of planetesimals. The aggregation of planetesimals within the snowline transition has been investigated by assessing the amalgamation history of the R chondrites breccias, a group of highly oxidised and brecciated chondrites that have undergone metamorphism. Chemical differences in orthopyroxene between clasts within these breccias shows that several bodies formed in close proximity to one another, but with different volatile contents. Some clasts show that they had been altered by serpentinisation-deserpentinisation reactions, whereas other clasts were equilibrated to the metal-olivine-pyroxene buffer. Since there was no distinct trend in petrographic type between these populations, this oxidation is likely to have occurred before the disruptive impact and reamalgamation of the R chondrite parent body. The R chondrite parent body is thus interpreted to be composed of an amalgamation of three or more distinct volatile-rich asteroids. Melting within planetesimals that formed near the snowline transition was investigated by performing experiments on the Karoonda CK chondrite. These experiments showed that a body that has been oxidised through reaction with water ice will produce a dense Fe-Ni-S-O melt at temperatures above 950°C. This melt wets silicate minerals, allowing it to develop an interconnected network and migrate rapidly towards a core via percolative flow. This wetting behaviour is only inhibited once large proportions of silicate melt has developed (above 1100°C). Hence, oxidised bodies are able to form cores at lower temperatures and more efficiently than their inner solar system counterparts, as metal melts in the refractory bodies are unable to wet silicates, and require high silicate melt fractions to migrate effectively. Although the primitive achondrites known as ureilites are not highly oxidised, they do contain a significant fraction of carbon, implying that their parent body accreted with a significant proportion of volatiles Ureilites display an unusual smelting texture developed at olivine grain boundaries, which has previously been attributed to a reduction reaction between olivine and graphite. However, fracture-based smelting was observed in many ureilites, along with typical of fluid-rock interaction. Redox modelling of different possible smelting reactions for known ureilite chemistries showed that graphite-based smelting cannot generate the observed compositions in smelted regions, but that a CH₄-H₂S-rich fluid could do so easily. This fluid could well have originated as a fluid exsolved from the crystallising core of the ureilite parent body. By understanding the aggregation, differentiation and devolatilisation processes of volatile-rich planetesimals, the ability for similar extrasolar planets to form conditions capable of supporting life for geologically significant times can be assessed. It is found that they are perhaps more favourable for life than the refractory inner solar system planets. Rock-ice bodies need to be treated differently when assessing their internal structure and evolution than those that formed in the relatively ice free inner solar system

Disequilibrium melting and melt migration driven by impacts : implications for rapid planetesimal core formation

The ε¹⁸²W ages of magmatic iron meteorites are largely within error of the oldest solar system particles, apparently requiring a mechanism for segregation of metals to the cores of planetesimals within 1.5million years of initial condensation. Currently favoured models involve equilibrium melting and gravitational segregation in a static, quiescent environment, which requires very high early heat production in small bodies via decay of short-lived radionuclides. However, the rapid accretion needed to do this implies a violent early accretionary history, raising the question of whether attainment of equilibrium is a valid assumption. Since our use of the Hf-W isotopic system is predicated on achievement of chemical equilibrium during core formation, our understanding of the timing of this key early solar system process is dependent on our knowledge of the segregation mechanism. Here, we investigate impact-related textures and microstructures in chondritic meteorites, and show that impact-generated deformation promoted separation of liquid FeNi into enlarged sulfide-depleted accumulations, and that this happened under conditions of thermochemical disequilibrium. These observations imply that similar enlarged metal accumulations developed as the earliest planetesimals grew by rapid collisional accretion. We suggest that the nonmagmatic iron meteorites formed this way and explain why they contain chondritic fragments in a way that is consistent with their trace element characteristics. As some planetesimals grew large enough to develop partially molten silicate mantles, these enlarged metal accumulations would settle rapidly to form cores leaving sulfide and small metal particles behind, since gravitational settling rate scales with the square of metal particle size. Our model thus provides a mechanism for more rapid core formation with less radiogenic heating. In contrast to existing models of core formation, the observed rarity of sulfide-dominant meteorites is an expected consequence of our model, which promotes early and progressive separation of metal and sulfide. We suggest that the core formation models that assume attainment of equilibrium in the Hf-W system underestimate the core formation time.19 page(s

Developing a database of systematic reviews of animal studies

Systematic reviews (SRs) are common practice in clinical and public health research, but less common in non-human animal research. Systematic reviews of animal studies can be valuable to inform clinical research, to evaluate the need for further animal experiments on a given topic, and to assess the hazard of an environmental exposure in the evaluation of toxicological studies. In the last 10 years, there has been an increase in the number of SRs of animal research, as well as several publications with detailed guidance on how to perform high-quality systematic reviews of experimental animal studies. In order to evaluate current analytical approaches used in SRs of animal studies, easily identify all systematic reviews on a specific topic, and subsequently the original animal studies and their results and promote awareness and understanding of these emerging approaches, we compiled a database of SRs of animal studies. The database was developed using a rigorous, systematic approach and covers a broad range of research fields: preclinical research, toxicology, environmental health, and veterinary medicine. The database currently includes 3113 SRs of animal studies (search date June 2019). In addition to bibliographical information, data on whether or not a risk of bias assessment and meta-analysis were conducted were extracted. For future users, the search features of the database provide users with a platform to identify and select SRs with a particular characteristic for export to Microsoft Word or Microsoft Excel. From there, users may perform additional data extraction to meet their research needs. The database is freely available at www.Mendeley.com (link). The database provides methodologists a comprehensive source that can be used to explore and advance the current methodology applied to SRs of animal studies, and can help researchers to easily identify all systematic reviews on a specific topic, and subsequently the original animal studies and their results and avoid duplication and unnecessary animal research