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Bedding Scale Correlation on Mars in Western Arabia Terra
No full textLayered rocks in the Arabia Terra region of Mars preserve a record of the planet's ancient climate. However, the exact formation mechanism of these rhythmically layered deposits is currently unknown. We previously proposed two distinct regionally correlative units of the Arabia Terra layered deposits based on their bedding thicknesses, orientation, and morphology from High Resolution Imaging Science Experiment stereo observations. For this work, we selected two adjacent craters in Arabia Terra, Sera and Jiji, for further study to test the proposed stratigraphic correlation. We constructed vertical stratigraphic sections of the deposits from dip-corrected bed thickness measurements and local stratigraphic correlations. We found that individual beds maintain a consistent thickness over kilometer scales but are somewhat variable at the basin scale. Each crater exhibited strata with a thinning-upward trend that terminated at terraces with inconsistent bedding, possibly indicating an equilibrium elevation for the formation mechanism. We also identified a probable stratigraphic correlation between basins using the similarities in bedding characteristics and patterns of measurable differences in bed-to-bed thicknesses, indicating synchronous strata. The planar bedding and uniform thickness of the beds within the deposits are consistent with airfall deposition over a prolonged geologic period. This process likely occurred under comparably dry conditions relative to the previously proposed depositional and diagenetic formation mechanisms
New age constraints support a K/Pg boundary interval on Vega Island, Antarctica: Implications for latest Cretaceous vertebrates and paleoenvironments
No full textA second K/Pg boundary interval in the northern sector of the Antarctic Peninsula on Vega Island has been proposed, yet current temporal resolution of these strata prohibits direct testing of this hypothesis. To not only test for the existence of a K/Pg boundary on Vega Island but also provide increased age resolution for the associated vertebrate fauna (e.g., marine reptiles, non-avian dinosaurs, and avian dinosaurs), the Vega Island succession was intensively re-sampled. Stratigraphic investigation of the Cape Lamb Member of the Snow Hill Island Formation, and in particular, the overlying Sandwich Bluff Member of the López de Bertodano Formation, was conducted using biostratigraphy, strontium isotope stratigraphy, magnetostratigraphy, and detrital zircon geochronology. These data indicate a Late Campanian–early Maastrichtian age for the Cape Lamb Member and present three possible correlations to the global polarity time scale (GPTS) for the overlying Sandwich Bluff Member. The most plausible correlation, which is consistent with biostratigraphy, detrital zircon geochronology, sequence stratigraphy, and all but one of the Sr-isotope ages, correlates the base of the section to C31N and the top of the section with C29N, which indicates that the K/Pg boundary passes through the top of the unit. A second, less plausible option conflicts with the biostratigraphy and depends on a series of poorly defined magnetic reversals in the upper part of the stratigraphy that also correlates the section between C31N and C29R and again indicates an inclusive K/Pg boundary interval. The least likely correlation, which depends on favoring only a single Srisotope age at the top of the section over biostratigraphy, correlates the section between C31N and C30N and is inconsistent with an included K/Pg boundary interval. Although our preferred correlation is well supported, we failed to identify an Ir-anomaly, spherules/impact ejecta, or other direct evidence typically used to define the precise position of a K/Pg boundary on Vega Island. This study does, however, confirm that Vegavis, from the base of the Sandwich Bluff Member, is the oldest (69.2–68.4 Ma) phylogenetically placed representative of the avian crown clade, and that marine vertebrates and non-avian dinosaurs persisted in Antarctica up to the terminal Cretaceous
Robust sampling for weak lensing and clustering analyses with the Dark Energy Survey
No full textRecent cosmological analyses rely on the ability to accurately sample from high-dimensional posterior distributions. A variety of algorithms have been applied in the field, but justification of the particular sampler choice and settings is often lacking. Here, we investigate three such samplers to motivate and validate the algorithm and settings used for the Dark Energy Survey (DES) analyses of the first 3 yr (Y3) of data from combined measurements of weak lensing and galaxy clustering. We employ the full DES Year 1 likelihood alongside a much faster approximate likelihood, which enables us to assess the outcomes from each sampler choice and demonstrate the robustness of our full results. We find that the ellipsoidal nested sampling algorithm multinest reports inconsistent estimates of the Bayesian evidence and somewhat narrower parameter credible intervals than the sliced nested sampling implemented in polychord. We compare the findings from multinest and polychord with parameter inference from the Metropolis–Hastings algorithm, finding good agreement. We determine that polychord provides a good balance of speed and robustness for posterior and evidence estimation, and recommend different settings for testing purposes and final chains for analyses with DES Y3 data. Our methodology can readily be reproduced to obtain suitable sampler settings for future surveys
VaTEST I: validation of sub-Saturn exoplanet TOI-181b in narrow orbit from its host star
No full textWe present here a validation of sub-Saturn exoplanet TOI-181b orbiting a K spectral type star TOI-181 (mass: 0.822 ± 0.04 M_⊙, radius: 0.745 ± 0.02 R_⊙, temperature: 4994 ± 50 K) as a part of Validation of Transiting Exoplanets using Statistical Tools (VaTEST) project. TOI-181b is a planet with radius 6.95 ± 0.08 R_⊕, mass 46.16 ± 2.71 M_⊕, orbiting in a slightly eccentric orbit with eccentricity 0.15 ± 0.06 and semimajor axis of 0.054 ± 0.004 au, with an orbital period of 4.5320 ± 0.000002 d. The transit photometry data were collected using Transiting Exoplanet Survey Satellite (TESS) and spectroscopic data for radial velocity analysis were collected using The European Southern Observatory’s (ESO) High Accuracy Radial Velocity Planet Searcher (HARPS) telescope. Based on the radial velocity best-fit model we measured RV semi-amplitude to be 20.56 ± 2.37 m s⁻¹. Additionally, we used VESPA and TRICERATOPS to compute the False Positive Probability (FPP), and the findings were FPP values of 1.68 × 10⁻¹⁴ and 3.81 × 10⁻⁰⁴, respectively, which are significantly lower than the 1 per cent threshold. The finding of TOI-181b is significant in the perspective of future work on the formation and migration history of analogous planetary systems since warm sub-Saturns are uncommon in the known sample of exoplanets
Position-specific carbon isotopes of Murchison amino acids elucidate extraterrestrial abiotic organic synthesis networks
No full textThe Murchison meteorite is a well-studied carbonaceous chondrite with relatively high concentrations of amino acids thought to be endogenous to the meteorite, in part because they are characterized by carbon isotope (δ¹³C) values higher than those typical of terrestrial amino acids. Past studies have proposed that extraterrestrial amino acids in the Murchison meteorite could have formed by Strecker synthesis (for α-amino acids), Michael addition (for β-amino acids), or reductive amination, but a lack of constraints have prevented confident discrimination among these possibilities, or assignment of specific formation pathways to each of several specific amino acids. Position-specific carbon isotope analysis differentiates amongst these mechanisms by relating molecular sites to isotopically distinct carbon sources and by constraining isotope effects associated with elementary chemical reactions. Prior measurements of the position-specific carbon isotopic composition of α-alanine from the Murchison CM chondrite demonstrated that alanine’s high δ¹³C_(VPDB) value is attributable to the amine carbon (δ¹³C_(VPDB) = +142 ± 20‰), consistent with Strecker synthesis drawing on ¹³C-rich carbonyl groups in precursors (L. Chimiak et al., Geochim. Cosmochim. Acta 292, 188–202, 2021). Here, we measured the δ¹³C composition of fragment ions generated by electron impact ionization of derivatized ⍺-alanine, β-alanine, and aspartic acid from Murchison via gas chromatography-Fourier transform mass spectrometry. α-Alanine’s amine carbon yielded δ¹³C_(VPDB) = +109 ± 21‰, which is consistent with the previously measured value and with formation from ¹³C-rich precursors. β-Alanine’s amine carbon presents a lower δ¹³C_(VPDB) = +33 ± 24‰, which supports formation from ¹³C-rich precursors but potentially via a Michael addition mechanism rather than Strecker synthesis. Aspartic acid’s amine carbon has δ¹³C_(VPDB)= –14±5‰, suggesting synthesis from precursors distinct from those that generated the alanine isomers. These measurements indicate that Murchison amino acids are a mixture of compounds made from different synthesis mechanisms, though some subsets likely drew on the same substrates; this conclusion highlights the complexity of extraterrestrial organic synthesis networks and the potential of emerging methods of isotope ratio analysis to elucidate the details of those networks
Deep Synoptic Array Science: Two Fast Radio Burst Sources in Massive Galaxy Clusters
No full textThe hot gas that constitutes the intracluster medium (ICM) has been studied at X-ray and millimeter/submillimeter wavelengths (Sunyaev–Zel'dovich effect) for decades. Fast radio bursts (FRBs) offer an additional method of directly measuring the ICM and gas surrounding clusters via observables such as dispersion measure (DM) and Faraday rotation measure. We report the discovery of two FRB sources detected with the Deep Synoptic Array whose host galaxies belong to massive galaxy clusters. In both cases, the FRBs exhibit excess extragalactic DM, some of which likely originate in the ICM of their respective clusters. FRB 20220914A resides in the galaxy cluster A2310 at z = 0.1125 with a projected offset from the cluster center of 520 ± 50 kpc. The host of a second source, FRB 20220509G, is an elliptical galaxy at z = 0.0894 that belongs to the galaxy cluster A2311 at the projected offset of 870 ± 50 kpc. These sources represent the first time an FRB has been localized to a galaxy cluster. We combine our FRB data with archival X-ray, Sunyaev–Zel'dovich (SZ), and optical observations of these clusters in order to infer properties of the ICM, including a measurement of gas temperature from DM and ySZ of 0.8–3.9 keV. We then compare our results to massive cluster halos from the IllustrisTNG simulation. Finally, we describe how large samples of localized FRBs from future surveys will constrain the ICM, particularly beyond the virial radius of clusters
Characteristics of interannual variability in space-based XCO₂ global observations
No full textAtmospheric carbon dioxide (CO₂) accounts for the largest radiative forcing among anthropogenic greenhouse gases. There is, therefore, a pressing need to understand the rate at which CO₂ accumulates in the atmosphere, including the interannual variations (IAVs) in this rate. IAV in the CO₂ growth rate is a small signal relative to the long-term trend and the mean annual cycle of atmospheric CO₂, and IAV is tied to climatic variations that may provide insights into long-term carbon–climate feedbacks. Observations from the Orbiting Carbon Observatory-2 (OCO-2) mission offer a new opportunity to refine our understanding of atmospheric CO₂ IAV since the satellite can measure over remote terrestrial regions and the open ocean, where traditional in situ CO₂ monitoring is difficult, providing better spatial coverage compared to ground-based monitoring techniques. In this study, we analyze the IAV of column-averaged dry-air CO₂ mole fraction (XCO₂) from OCO-2 between September 2014 and June 2021. The amplitude of the IAV, which is calculated as the standard deviation of the time series, is up to 1.2 ppm over the continents and around 0.4 ppm over the open ocean. Across all latitudes, the OCO-2-detected XCO₂ IAV shows a clear relationship with El Niño–Southern Oscillation (ENSO)-driven variations that originate in the tropics and are transported poleward. Similar, but smoother, zonal patterns of OCO-2 XCO₂ IAV time series compared to ground-based in situ observations and with column observations from the Total Carbon Column Observing Network (TCCON) and the Greenhouse Gases Observing Satellite (GOSAT) show that OCO-2 observations can be used reliably to estimate IAV. Furthermore, the extensive spatial coverage of the OCO-2 satellite data leads to smoother IAV time series than those from other datasets, suggesting that OCO-2 provides new capabilities for revealing small IAV signals despite sources of noise and error that are inherent to remote-sensing datasets
A wireless patch for the monitoring of C-reactive protein in sweat
No full textThe quantification of protein biomarkers in blood at picomolar-level sensitivity requires labour-intensive incubation and washing steps. Sensing proteins in sweat, which would allow for point-of-care monitoring, is hindered by the typically large interpersonal and intrapersonal variations in its composition. Here we report the design and performance of a wearable and wireless patch for the real-time electrochemical detection of the inflammatory biomarker C-reactive (CRP) protein in sweat. The device integrates iontophoretic sweat extraction, microfluidic channels for sweat sampling and for reagent routing and replacement, and a graphene-based sensor array for quantifying CRP (via an electrode functionalized with anti-CRP capture antibodies-conjugated gold nanoparticles), ionic strength, pH and temperature for the real-time calibration of the CRP sensor. In patients with chronic obstructive pulmonary disease, with active or past infections or who had heart failure, the elevated concentrations of CRP measured via the patch correlated well with the protein’s levels in serum. Wearable biosensors for the real-time sensitive analysis of inflammatory proteins in sweat may facilitate the management of chronic diseases
Quantitative measurement of the requirement of diverse protein degradation pathways in MHC class I peptide presentation
No full textPeptides from degradation of intracellular proteins are continuously displayed by major histocompatibility complex (MHC) class I. To better understand origins of these peptides, we performed a comprehensive census of the class I peptide repertoire in the presence and absence of ubiquitin-proteasome system (UPS) activity upon developing optimized methodology to enrich for and quantify these peptides. Whereas most class I peptides are dependent on the UPS for their generation, a surprising 30%, enriched in peptides of mitochondrial origin, appears independent of the UPS. A further ~10% of peptides were found to be dependent on the proteasome but independent of ubiquitination for their generation. Notably, clinically achievable partial inhibition of the proteasome resulted in display of atypical peptides. Our results suggest that generation of MHC class I•peptide complexes is more complex than previously recognized, with UPS-dependent and UPS-independent components; paradoxically, alternative protein degradation pathways also generate class I peptides when canonical pathways are impaired
Mechanism of Hydrogen Peroxide Formation on Sprayed Water Microdroplets
No full textHow is H₂O₂ formed in sprayed water is not well understood. It is believed to involve the association of HO• radicals spontaneously generated from HO– ions by internal electric fields on the surface of neutral microdroplets. Spraying water actually creates charged microdroplets carrying either excess OH– or H+ intrinsic ions that repel each other toward the very surface. The requisite electron transfer (ET) takes place between surface-bound ions: HOS– + HS+ = HOS• + HS•, during encounters between positive and negative microdroplets. The ET endothermicity in bulk water (ΔH = 448 kJ mol⁻¹) is reversed in low-density surface water by the destabilization of the strongly hydrated reactant ions: ΔHhydration(H+ + OH–) = −1670 kJ mol⁻¹, relative to neutral radical products: ΔHhydration(HO• + H•) = −58 kJ mol⁻¹. The formation of H₂O₂ is driven by the energy supplied for spraying water, and caused by restricted hydration on microdroplet surfaces