Micrometeorite collections: a review and their current status.

Micrometeorites are estimated to represent the main part of the present flux of extraterrestrial matter found on the Earth's surface and provide valuable samples to probe the interplanetary medium. Here, we describe large and representative collections of micrometeorites currently available to the scientific community. These include Antarctic collections from surface ice and snow, as well as glacial sediments from the eroded top of nunataks-summits outcropping from the icesheet-and moraines. Collections extracted from deep-sea sediments (DSS) produced a large number of micrometeorites, in particular, iron-rich cosmic spherules that are rarer in other collections. Collections from the old and stable surface of the Atacama Desert show that finding large numbers of micrometeorites is not restricted to polar regions or DSS. The advent of rooftop collections marks an important step into involving citizen science in the study of micrometeorites, as well as providing potential sampling locations over all latitudes to explore the modern flux. We explore their strengths of the collections to address specific scientific questions and their potential weaknesses. The future of micrometeorite research will involve the finding of large fossil micrometeorite collections and benefit from recent advances in sampling cosmic dust directly from the air. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Weaker axially dipolar time-averaged paleomagnetic field based on multidomain-corrected paleointensities from Galapagos lavas.

The geomagnetic field is predominantly dipolar today, and high-fidelity paleomagnetic mean directions from all over the globe strongly support the geocentric axial dipole (GAD) hypothesis for the past few million years. However, the bulk of paleointensity data fails to coincide with the axial dipole prediction of a factor-of-2 equator-to-pole increase in mean field strength, leaving the core dynamo process an enigma. Here, we obtain a multidomain-corrected Pliocene-Pleistocene average paleointensity of 21.6 ± 11.0 µT recorded by 27 lava flows from the Galapagos Archipelago near the Equator. Our new result in conjunction with a published comprehensive study of single-domain-behaved paleointensities from Antarctica (33.4 ± 13.9 µT) that also correspond to GAD directions suggests that the overall average paleomagnetic field over the past few million years has indeed been dominantly dipolar in intensity yet only ∼ 60% of the present-day field strength, with a long-term average virtual axial dipole magnetic moment of the Earth of only 4.9 ± 2.4 × 10(22) A ⋅ m(2).

Mutation of UL24 impedes the dissemination of acute herpes simplex virus 1 infection from the cornea to neurons of trigeminal ganglia.

Herpes simplex virus 1 (human herpesvirus 1) initially infects epithelial cells of the mucosa and then goes on to infect sensory neurons leading ultimately to a latent infection in trigeminal ganglia (TG). UL24 is a core herpesvirus gene that has been identified as a determinant of pathogenesis in several Alphaherpesvirinae, although the underlying mechanisms are unknown. In a mouse model of ocular infection, a UL24-deficient virus exhibited a reduction in viral titres in tear films of 1 log10, whilst titres in TG are often below the level of detection. Moreover, the efficiency of reactivation from latency was also severely reduced. Herein, we investigated how UL24 contributed to acute infection of TG. Our results comparing the impact of UL24 on viral titres in eye tissue versus in tear films did not reveal a general defect in virus release from the cornea. We also found that the impairment of replication seen in mouse primary embryonic neurons with a UL24-deficient virus was not more severe than that observed in an epithelial cell line. Rather, in situ histological analyses revealed that infection with a UL24-deficient virus led to a significant reduction in the number of acutely infected neurons at 3 days post-infection (p.i.). Moreover, there was a significant reduction in the number of neurons positive for viral DNA at 2 days p.i. for the UL24-deficient virus as compared with that observed for WT or a rescue virus. Our results supported a model whereby UL24 functions in the dissemination of acute infection from the cornea to neurons in TG.

Impact glasses from Belize represent tektites from the Pleistocene Pantasma impact crater in Nicaragua.

Tektites are terrestrial impact-generated glasses that are ejected long distance (up to 11,000 km), share unique characteristics and have a poorly understood formation process. Only four tektite strewn-fields are known, and three of them are sourced from known impact craters. Here we show that the recently discovered Pantasma impact crater (14 km diameter) in Nicaragua is the source of an impact glass strewn-field documented in Belize 530 km away. Their cogenesis is documented by coincidental ages, at 804 ± 9 ka, as well as consistent elemental compositions and isotopic ratios. The Belize impact glass share many characteristics with known tektites but also present several peculiar features. We propose that these glasses represent a previously unrecognized tektite strewn-field. These discoveries shed new light on the tektite formation process, which may be more common than previously claimed, as most known Pleistocene >10 km diameter cratering events have generated tektites.

Continuous presence of proto-cereals in Anatolia since 2.3 Ma, and their possible co-evolution with large herbivores and hominins.

Cereals are a central resource for the human diet and are traditionally assumed to have evolved from wild grasses at the onset of the Neolithic under the pressure of agriculture. Here we demonstrate that cereals may have a significantly longer and more diverse lineage, based on the study of a 0-2.3 Ma, 601 m long sedimentary core from Lake Acigöl (South-West Anatolia). Pollen characteristic of cereals is abundant throughout the sedimentary sequence. The presence of large lakes within this arid bioclimatic zone led to the concentration of large herbivore herds, as indicated by the continuous occurrence of coprophilous fungi spores in the record. Our hypothesis is that the effects of overgrazing on soils and herbaceous stratum, during this long period, led to genetic modifications of the Poaceae taxa and to the appearance of proto-cereals. The simultaneous presence of hominins is attested as early as about 1.4 Ma in the lake vicinity, and 1.8 Ma in Georgia and Levant. These ancient hominins probably benefited from the availability of these proto-cereals, rich in nutrients, as well as various other edible plants, opening the way, in this region of the Middle East, to a process of domestication, which reached its full development during the Neolithic.

Differential importance of highly conserved residues in UL24 for herpes simplex virus 1 replication in vivo and reactivation.

The UL24 gene of herpes simplex virus 1 (HSV-1) is widely conserved among all subfamilies of the Herpesviridae. It is one of only four HSV-1 genes for which mutations have been mapped that confer a syncytial plaque phenotype. In a mouse model of infection, UL24-deficient viruses exhibit reduced titres, particularly in neurons, and an apparent defect in reactivation from latency. There are several highly conserved residues in UL24; however, their importance in the role of UL24 in vivo is unknown. In this study, we compared virus strains with substitution mutations corresponding to the PD-(D/E)XK endonuclease motif of UL24 (vUL24-E99A/K101A) or a substitution of another highly conserved residue (vUL24-G121A). Both mutant viruses cause the formation of syncytial plaques at 39 degrees C; however, we found that the viruses differed dramatically when tested in a mouse model of infection. vUL24-E99A/K101A exhibited titres in the eye that were 10-fold lower than those of the wild-type virus KOS, and titres in trigeminal ganglia (TG) that were more than 2 log10 lower. Clinical signs were barely detectable with vUL24-E99A/K101A. Furthermore, the percentage of TG from which virus reactivated was also significantly lower for this mutant than for KOS. In contrast, vUL24-G121A behaved similarly to the wild-type virus in mice. These results are consistent with the endonuclease motif being important for the role of UL24 in vivo and also imply that the UL24 temperature-dependent syncytial plaque phenotype can be separated genetically from several in vivo phenotypes.

3D X-ray tomographic analysis reveals how coesite is preserved in Muong Nong-type tektites.

Muong Nong-type (MN) tektites are a layered type of tektite associated to the Australasian strewn field, the youngest (790 kyr) and largest on Earth. In some MN tektites, coesite is observed in association with relict quartz and silica glass within inclusions surrounded by a froth layer. The formation of coesite-bearing frothy inclusions is here investigated through a 3D textural multiscale analysis of the vesicles contained in a MN tektite sample, combined with compositional and spectroscopic data. The vesicle size distribution testifies to a post-shock decompression that induced melting and extensive vesiculation in the tektite melt. Compared to free vesicles, nucleated homogeneously in the tektite melt, froth vesicles nucleated heterogeneously on relict quartz surfaces at the margins of coesite-bearing inclusions. The rapid detachment of the froth vesicles and prompt reactivation of the nucleation site favoured the packing of vesicles and the formation of the froth structure. Vesicle relaxation time scales suggest that the vesiculation process lasted few seconds. The formation of the froth layer was instrumental for the preservation of coesite, promoting quenching of the inclusion core through the subtraction of heat during froth expansion, thereby physically insulating the inclusion until the final quench of the tektite melt.

Complete Genome Sequence of a New Member of the Marseilleviridae Recovered from the Brackish Submarine Spring in the Cassis Port-Miou Calanque, France.

Marseilleviridae is a rapidly expanding family of Acanthamoeba-infecting large DNA viruses distributed worldwide. We report here the complete 349-kbp genome sequence of Port-Miou virus, which is surprisingly close to that of Lausannevirus (isolated from the Seine River upstream from Paris, France), despite the strong dissimilarities of their sampling locations.

Visualization of mouse neuronal ganglia infected by Herpes Simplex Virus 1 (HSV-1) using multimodal non-linear optical microscopy.

Herpes simplex virus 1 (HSV-1) is a neurotropic virus that causes skin lesions and goes on to enter a latent state in neurons of the trigeminal ganglia. Following stress, the virus may reactivate from latency leading to recurrent lesions. The in situ study of neuronal infections by HSV-1 is critical to understanding the mechanisms involved in the biology of this virus and how it causes disease; however, this normally requires fixation and sectioning of the target tissues followed by treatment with contrast agents to visualize key structures, which can lead to artifacts. To further our ability to study HSV-1 neuropathogenesis, we have generated a recombinant virus expressing a second generation red fluorescent protein (mCherry), which behaves like the parental virus in vivo. By optimizing the application of a multimodal non-linear optical microscopy platform, we have successfully visualized in unsectioned trigeminal ganglia of mice both infected cells by two-photon fluorescence microscopy, and myelinated axons of uninfected surrounding cells by coherent anti-Stokes Raman scattering (CARS) microscopy. These results represent the first report of CARS microscopy being combined with 2-photon fluorescence microscopy to visualize virus-infected cells deep within unsectioned explanted tissue, and demonstrate the application of multimodal non-linear optical microscopy for high spatial resolution biological imaging of tissues without the use of stains or fixatives.

The UL24 protein of herpes simplex virus 1 affects the sub-cellular distribution of viral glycoproteins involved in fusion.

Mutations in UL24 of herpes simplex virus type 1 can lead to a syncytial phenotype. We hypothesized that UL24 affects the sub-cellular distribution of viral glycoproteins involved in fusion. In non-immortalized human foreskin fibroblasts (HFFs) we detected viral glycoproteins B (gB), gD, gH and gL present in extended blotches throughout the cytoplasm with limited nuclear membrane staining; however, in HFFs infected with a UL24-deficient virus (UL24X), staining for the viral glycoproteins appeared as long, thin streaks running across the cell. Interestingly, there was a decrease in co-localized staining of gB and gD with F-actin at late times in UL24X-infected HFFs. Treatment with chemical agents that perturbed the actin cytoskeleton hindered the formation of UL24X-induced syncytia in these cells. These data support a model whereby the UL24 syncytial phenotype results from a mislocalization of viral glycoproteins late in infection.

Radar-enabled recovery of the Sutter's Mill meteorite, a carbonaceous chondrite regolith breccia.

Doppler weather radar imaging enabled the rapid recovery of the Sutter's Mill meteorite after a rare 4-kiloton of TNT-equivalent asteroid impact over the foothills of the Sierra Nevada in northern California. The recovered meteorites survived a record high-speed entry of 28.6 kilometers per second from an orbit close to that of Jupiter-family comets (Tisserand's parameter = 2.8 ± 0.3). Sutter's Mill is a regolith breccia composed of CM (Mighei)-type carbonaceous chondrite and highly reduced xenolithic materials. It exhibits considerable diversity of mineralogy, petrography, and isotope and organic chemistry, resulting from a complex formation history of the parent body surface. That diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to C-class asteroids are interpreted.

Nonmagnetic high pressure cell for magnetic remanence measurements up to 1.5 GPa in a superconducting quantum interference device magnetometer.

We describe here a compact nonmagnetic composite high pressure cell of piston-cylinder type with inner diameter of 6 mm equipped with manganin pressure sensor. This cell was developed for room temperature measurements of magnetic remanence of relatively large rock samples (up to 5.8 mm in diameter and 15 mm long cylinders) under hydrostatic pressure up to 1.5 GPa (the operating pressure limit) in the 2G Enterprises superconducting quantum interference device magnetometer. Its design was focused on minimizing the remanent magnetic moment m(r) of the cell (m(r)=3 x 10(-8) A m(2)) that allowed direct measurements of remanent magnetic moment M(r) under pressure for weakly magnetic materials-rock samples (M(r) epsilon[5 x 10(-7),10(-4)] A m(2)). The inner part of this composite cell is made of hard "Russian alloy" (Ni(57)Cr(40)Al(3)) whereas the envelope of the cell corps is made of less magnetic titanium alloy. This design solution permitted to reduce the total remanent magnetic moment of the whole cell and represents the main device feature. We describe here the choice of materials for pressure cell based on their magnetic and mechanical properties, the choice of the pressure transmitting medium (polyethilsiloxane liquid) providing perfectly hydrostatic conditions for the sample as well as the cell geometry. The cell performance is illustrated by results of pressure demagnetization experiments on rocks and minerals.