Thermal shock fragmentation of Mg silicates within scoriaceous micrometeorites reveal hydrated asteroidal sources

Scoriaceous micrometeorites are highly vesicular extraterrestrial dust particles that have experienced partial melting during atmospheric entry. We report the occurrence of clusters of anhedral relict forsterite crystals within these particles that testify to in situ fragmentation. The absence of similar clusters within unmelted micrometeorites suggests that fragmentation occurs during atmospheric entry rather than by parent body shock reprocessing. Clusters of broken forsterite crystals are shown to form as a result of fracturing owing to thermal stress developed during entry heating and require thermal gradients of >200 K µm–1 in order for differential thermal expansion to exceed the critical shear strength of olivine. Thermal gradients of this magnitude significantly exceed those resulting from thermal conduction and require the endothermic decomposition of phyllosilicates. Fragmented relict forsterite within scoriaceous micrometeorites, therefore, indicate that the precursor grains were similar to CI and CM2 chondrites and retained phyllosilicate prior to atmospheric entry and thus were not dehydrated on the parent asteroid by shock or thermal metamorphism. Explosive fragmentation of hydrous asteroids during collisions, therefore, does not significantly bias the interplanetary dust population

Olivine settling in cosmic spherules during atmospheric deceleration: An indicator of the orbital eccentricity of interplanetary dust

A new type of cosmic spherule is reported with textures suggesting settling of olivine during atmospheric deceleration. Numerical simulations of entry heating reveal that relict forsterite, which survives melting, can settle over the 1–2 s of flight at high entry angles and entry velocities up to 16 km s−1. Enhanced crystallization of phenocrysts by heterogeneous nucleation on accumulated relict forsterites is the most likely origin of the observed cumulate textures in cosmic spherules. Such textures in cosmic spherules reveal interplanetary dust with higher encounter velocity with the Earth that correspond to orbital eccentricities >0.3. The relative abundance of cumulate spherules suggests that 14% of ordinary chondrite‐related, S(IV)‐type asteroid dust over the last 800 kyr had relatively high orbital eccentricity owing to secular and planetary perturbations. The textures of cosmic spherules collected from sediments can therefore be used to trace dust orbital variations with time, which may influence terrestrial climate

Micrometeorites: Insights into the flux, sources and atmospheric entry of extraterrestrial dust at Earth

Micrometeorites (MMs) provide constraints on the flux and sources of extraterrestrial dust falling on Earth as well as recording the processes occurring during atmospheric entry. Collections of micrometeorites have been recovered from a wide variety of environments including Antarctic moraine, rock traps, ice and snow and on roof tops in urban areas. Studies of the mineralogy and composition of MMs suggest that most particles (>98%) >50 ​μm in diameter have asteroidal sources, whilst ~50% of particles smaller than 50 ​μm are likely to be derived from comets. The relative abundance of S(IV)-type asteroid materials, similar to ordinary chondrites increases with size, although C-type asteroidal materials, similar to carbonaceous chondrites dominate over all. Although MMs provide excellent evidence on the nature and abundance of extraterrestrial dust at the Earth’s orbit they are not without bias and uncertainty. Mineralogical and compositional change during atmospheric entry makes the exact nature of their precursors uncertain complicating evaluation of source beyond basic classes of material. This is particularly true at larger sizes when complete melting to form cosmic spherules occurs, however, unmelted MMs >50 ​μm in size are also often thermally altered. Mixing with atmospheric oxygen and mass fractionation by evaporation furthermore complicates the use of oxygen isotope compositions in identifying parent bodies. All MM collections are suggested to exhibit biases owing to: (1) collection method, (2) terrestrial weathering, (3) terrestrial contamination, and (4) erosion and deposition by terrestrial surface processes. Even in the least biased collections, those collected by dedicated melting of Antarctic snow, erosive loss of material is suggested here to make fluxes uncertain by factors of up to ~2. The abundance of asteroid-derived MMs observed in collections contradicts models of the orbital evolution of interplanetary dust to Earth, which suggests >70% should be provided by comets

Securing Safe Supply During COVID-19 and Beyond: Scoping Review and Knowledge Mobilization

Background Safe supply is defined as the legal and regulated provision of drugs with mind and/or body altering properties that have been typically accessible only through the illegal drug market. In response to the coronavirus disease 2019 (COVID-19) pandemic and related social/physical distancing measures, efforts have been made to scale up and increase access to safe supply programs in an effort to reduce overdose and other drug- and drug policy-related risks. However, it remains unclear whether these efforts taken thus far have meaningfully mitigated the barriers to safe supply experienced by People Who Use Drugs (PWUD), both during and beyond the context of COVID-19. We thus undertook a scoping review to identify key concepts, strategies and gaps in evidence with respect to the provision of safe supply during pandemics and other emergencies. Methods We conducted three searches across Scopus, Medline, Embase, CINAHL, and The Cochrane Central Register of Controlled Trials (CENTRAL) for peer-reviewed and grey literature articles to understand barriers/facilitators to both accessing and prescribing legal, pharmaceutical-grade drugs, including opioids, benzodiazepines, and/or stimulants during public health emergencies from January 1 2002 to June 30 2020. We also included opioid agonist therapies (OAT) during emergency conditions. All potential sources underwent title/abstract screening and duplicate full- text review to determine eligibility for inclusion. Three reviewers extracted characteristics and barriers/facilitators to accessing or prescribing drugs for each study, and these were then inductively analyzed to identify common themes. Key stakeholders (PWUD, prescribers, and policymakers/regulators) informed the search strategy and validated findings and interpretations. Input from PWUD and prescribers was gathered through Advisory Committee meetings and one-on-one consultations, respectively. Results We screened 9,839 references and included 169 studies (135 peer-reviewed articles and 36 grey literature reports). From 119 articles, we identified 35 themes related to barriers/facilitators to prescribing safe supply or OAT. Few studies (n=24) focused on emergency or pandemic contexts. Among the most frequently reported barriers were restrictive laws or policies (n= 33; 28%). The most frequently cited facilitator was temporary legal or regulatory exemptions (n= 16; 13%). Further stakeholder consultation identified barriers/facilitators to safe supply absent in the reviewed literature: PWUD reported barriers including lack of access to desired substances, concerns about child apprehension, and a lack of cultural competency within safe supply/OAT programs; prescribers reported barriers including regional differences in service delivery, colleague support, and a lack of, or disagreement between, clinical guidance documents. Conclusion We identified multiple barriers and facilitators to accessing and/or prescribing safe supply or OAT. With few peer-reviewed studies on safe supply models, particularly in the context of emergencies, input from PWUD and other stakeholders offered crucial insights not reflected in the existing literature. To address the overdose epidemic stemming from the criminalization of an unregulated drug supply, prescribers, regulators, and public health authorities should focus on scaling up, and then evaluating, diverse safe supply frameworks that address the facilitators and barriers we have identified

The mineralogy and petrology of I-type cosmic spherules: Implications for their sources, origins and identification in sedimentary rocks

I-type cosmic spherules are micrometeorites that formed by melting during atmospheric entry and consist mainly of iron oxides and FeNi metal. I-types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time. We report the results of a study of the mineralogy and petrology of 88 I-type cosmic spherules recovered from Antarctica in order to evaluate how they formed and evolved during atmospheric entry, to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks. Two textural types of I-type cosmic spherule are recognised: (1) metal bead-bearing (MET) spherules dominated by Ni-poor (100 and suggest that metal from H-group ordinary, CM, CR and iron meteorites may form the majority of particles. Oxidation during entry heating increases in the series MET 80 wt% Ni comprising a particle mass fraction of <0.2. Non-equilibrium effects in the exchange of Ni between wüstite and metal, and magnetite and wüstite are suggested as proxies for the rate of oxidation and cooling rate respectively. Variations in magnetite and wüstite crystal sizes are also suggested to relate to cooling rate allowing relative entry angle of particles to be evaluated. The formation of secondary metal in the form of sub-micron Ni-rich or Pt-group nuggets and as symplectite with magnetite was also identified and suggested to occur largely due to the exsolution of metallic alloys during decomposition of non-stoichiometric wüstite. Weathering is restricted to replacement of metal by iron hydroxides. The following criteria are recommended for the conclusive identification of I-type spherules within sediments and sedimentary rocks: (i) spherical particle morphologies, (ii) dendritic crystal morphologies, (iii) the presence of wüstite and magnetite, (iv) Ni-bearing wüstite and magnetite, and (v) the presence of relict FeNi metal

Evaluation of an emergency safe supply drugs and managed alcohol program in COVID-19 isolation hotel shelters for people experiencing homelessness

BACKGROUND: During a COVID-19 outbreak in the congregate shelter system in Halifax, Nova Scotia, Canada, a multidisciplinary health care team provided an emergency “safe supply” of pharmaceutical-grade medications and beverage-grade alcohol to facilitate isolation in COVID-19 hotel shelters for residents who are dependent on these substances. We aimed to evaluate (a) substances and dosages provided, and (b) effectiveness and safety of the program. METHODS: We retrospectively reviewed medical records of all COVID-19 isolation hotel shelter residents during May 2021. We extracted data on medication and alcohol dosages provided each day. The primary outcome was residents prematurely leaving isolation against public health orders. Adverse events included (a) overdose; (b) intoxication; and (c) diversion, selling, or sharing of medications or alcohol. RESULTS: Over 25 days, 77 isolation hotel residents were assessed (mean age 42 ± 14 years; 24% women). Sixty-two (81%) residents were provided medications, alcohol, or cigarettes. Seventeen residents (22%) received opioid agonist treatment medications (methadone, buprenorphine, or slow-release oral morphine) and 27 (35%) received hydromorphone tablets. Thirty-one (40%) residents received stimulant tablets with methylphenidate (27; 35%), dextroamphetamine (8; 10%), or lisdexamfetamine (2; 3%). Six residents (8%) received benzodiazepines. Forty-two (55%) residents received alcohol, including 41 (53%) with strong beer, three (3%) with wine, and one (1%) with hard liquor. Over 14 days in isolation, mean daily dosages increased of hydromorphone (45 ± 32 to 57 ± 42mg), methylphenidate (51 ± 28 to 77 ± 37mg), dextroamphetamine (33 ± 16 to 46 ± 13mg), and alcohol (12.3 ± 7.6 to 13.0 ± 6.9 standard drinks). Six residents (8%) left isolation prematurely, but four of those residents returned. Over 1,059 person-days in isolation, there were zero overdoses. Documented concerns regarding intoxication occurred six times (0.005 events/person-day) and medication diversion or sharing three times (0.003 events/person-day). CONCLUSIONS: An emergency safe supply and managed alcohol program, paired with housing, was associated with low rates of adverse events and high rates of successful completion of the 14-day isolation period in COVID-19 isolation hotel shelters. This supports the effectiveness and safety of emergency safe supply prescribing and managed alcohol in this setting

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

Winchcombe: an example of rapid terrestrial alteration of a CM chondrite

Winchcombe is a CM chondrite that fell in England on February 28, 2021. Its rapid retrieval was well characterized. Within two polished sections of Winchcombe, terrestrial phases were observed. Calcite and calcium sulfates were found in a sample recovered from a field on March 6, 2021, and halite was observed on a sample months after its recovery from a driveway on March 2, 2021. These terrestrial phases were characterized by scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. Calcite veins crosscut the fusion crust and therefore postdate it. The calcite likely precipitated in the damp environment (sheep field) where the meteorite lay for six days prior to its retrieval. The sulfates occur on the edges of the sample and were identified as three minerals: gypsum, bassanite, and anhydrite. Given that the sulfates occur only on the sample's edges, including on top of the fusion crust, they formed after Winchcombe fell. Sulfate precipitation is attributed to the damp fall environment, likely resulted from sulfide-derived H2S reacting with calcite within the meteorite. Halite occurs as euhedral crystals only on the surface of a polished section and exclusively in areas relatively enriched in sodium. It was likely produced by the interaction of the polished rock slice with the humid laboratory air over a period of months. The sulfates, fusion crust calcite, and halite all post-date Winchcombe's entry into the Earth's atmosphere and showcase how rapidly meteorite falls can be terrestrially altered

The Winchcombe meteorite – a regolith breccia from a rubble-pile CM chondrite asteroid

The Winchcombe meteorite is a CM chondrite breccia composed of eight distinct lithological units plus a cataclastic matrix. The degree of aqueous alteration varies between intensely altered CM2.0 and moderately altered CM2.6. Although no lithology dominates, three heavily altered rock types (CM2.1-2.3) represent >70 area%. Tochilinite-cronstedtite intergrowths (TCIs) are common in several lithologies. Their compositions can vary significantly, even within a single lithology, which can prevent a clear assessment of alteration extent if only TCI composition is considered. We suggest this is due to early alteration under localised geochemical microenvironments creating a diversity of compositions and because later reprocessing was incomplete, leaving a record of the parent body’s fluid history. In Winchcombe fragments of primary accretionary rock are held within a cataclastic matrix (~15 area%). This material is impact-derived fallback debris. Its grain size and texture suggest that the disruption of the original parent asteroid responded by intergranular fracture at grain sizes <100 µm, while larger phases, such as whole chondrules, splintered apart. Re-accretion formed a poorly lithified body. During atmospheric entry, the Winchcombe meteoroid broke apart with new fractures preferentially cutting through the weaker cataclastic matrix and separating the breccia into its component clasts. The strength of the cataclastic matrix imparts a control on the survival of CM chondrite meteoroids. Winchcombe’s unweathered state and diversity of lithologies makes it an ideal sample for exploring the geological history of the CM chondrite group.Additional authors: H. Mansour, S. Piazolo, T. Salge, R. Heard, R. Findlay, A. J. King, H. C. Bates, M. R. Lee, N. R. Stephen, F. M. Willcocks, R. C. Greenwood, I. A. Franchi, S. S. Russell, C. S. Harrison, P. F. Schofield, N. V. Almeida, C. Floyd, P.-E. Martin, K. H. Joy, P. J. Wozniakiewicz, D. Hallatt, M. J. Burchell, L. S. Alesbrook, V. Spathis, L. T. Cornwell, A. Digna

Long-lived magnetism on chondrite parent bodies

publisher: Elsevier articletitle: Long-lived magnetism on chondrite parent bodies journaltitle: Earth and Planetary Science Letters articlelink: http://dx.doi.org/10.1016/j.epsl.2017.07.035 content_type: article copyright: © 2017 The Authors. Published by Elsevier B.V.© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). The attached file is the published version of the article