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Ancient shorelines on Mars must have formed before and during the emplacement of the Tharsis volcanic province, instead of afterwards as previously assumed, suggesting that oceans on Mars formed early. Dating the Martian ocean The observation of potential palaeo-shorelines around the northern plains of Mars points to the existence of an ancient Martian ocean. However, these features do not seem to follow an equipotential surface, which would argue against an oceanic origin. The varying elevation of these shorelines could be explained by true polar wander occurring after the formation of Tharsis, a volcanic province that dominates the gravity and topography of Mars. However, this would require Tharsis to have formed far from the equator, which is thought to be unlikely. Robert Citron and co-authors show that variations in shoreline topography can instead be explained if the shorelines formed before and during the emplacement of Tharsis, implying that oceans formed early on Mars, potentially in relation to the initiation and decline of Tharsis volcanism. Widespread evidence points to the existence of an ancient Martian ocean 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . Most compelling are the putative ancient shorelines in the northern plains 2 , 7 . However, these shorelines fail to follow an equipotential surface, and this has been used to challenge the notion that they formed via an early ocean 9 and hence to question the existence of such an ocean. The shorelines’ deviation from a constant elevation can be explained by true polar wander occurring after the formation of Tharsis 10 , a volcanic province that dominates the gravity and topography of Mars. However, surface loading from the oceans can drive polar wander only if Tharsis formed far from the equator 10 , and most evidence indicates that Tharsis formed near the equator 11 , 12 , 13 , 14 , 15 , meaning that there is no current explanation for the shorelines’ deviation from an equipotential that is consistent with our geophysical understanding of Mars. Here we show that variations in shoreline topography can be explained by deformation caused by the emplacement of Tharsis. We find that the shorelines must have formed before and during the emplacement of Tharsis, instead of afterwards, as previously assumed. Our results imply that oceans on Mars formed early, concurrent with the valley networks 15 , and point to a close relationship between the evolution of oceans on Mars and the initiation and decline of Tharsis volcanism, with broad implications for the geology, hydrological cycle and climate of early Mars.

The formation and evolution of the South Pole‐Aitken (SPA) basin is critical to relating large impact basin formation and modification to lunar geophysical evolution. Most prior models of the SPA impact were conducted in 2D, making it difficult to compare model output to the 3D crustal structure and ejecta distribution. In order to better constrain the parameters of the SPA impactor and the expected post impact distribution of crust and ejecta, we conducted numerical simulations of the SPA impact in 3D. We tested a wide range of impact parameters and constrained model results with recent geophysical data. We found the crustal structure of the SPA basin is best fit by an oblique impact (30–45°) of a 350–400 km diameter projectile impacting at 12–16 km/s. The impact excavated material from as deep as 80–120 km, and ejecta was deposited in a butterfly pattern with a forbidden region uprange of the impact. Plain Language Summary The South Pole‐Aitken (SPA) basin is the largest impact‐generated structure on the Moon. The large size of the basin (approximately 1,500–2,000 km in diameter) implies the impact that generated the basin globally influenced the early evolution of the Moon. In order to constrain the type of impact that formed the basin, we ran computer simulations of large projectiles (300–400 km in diameter) impacting the early lunar surface. We found the structure of the crust surrounding the basin best matches an impact of a 350–400 km diameter projectile (similar in scale to Saturn's moon Mimas) impacting the Moon with a velocity of 12–16 km per second. Our computer models show that the collision that generated the basin would have formed a non‐symmetrical distribution of impact ejecta, and excavated material from the lower crust and upper mantle. Our results constrain the type of impact that formed the SPA basin, and suggest that ejecta from the impact is prevalent at sites of current and future lunar exploration. Key Points 3D simulations constrain the South Pole‐Aitken (SPA) impactor to 350–400 km diameter impacting at 12–16 km/s and 30–45° The SPA impact excavated lower crust and upper mantle lunar materials, and emplaced ejecta in a butterfly type ejecta pattern The thick crustal annulus present in model results requires further modeling of basin collapse and post‐impact relaxation

Understanding the longevity of Mars’s dynamo is key to interpreting the planet’s atmospheric loss history and the properties of its deep interior. Satellite data showing magnetic lows above many large impact basins formed 4.1-3.7 billion years ago (Ga) have been interpreted as evidence that Mars’s dynamo terminated before 4.1 Ga—at least 0.4 Gy before intense late Noachian/early Hesperian hydrological activity. However, evidence for a longer-lived, reversing dynamo from young volcanics and the Martian meteorite ALH 84001 supports an alternative interpretation of Mars’s apparently demagnetized basins. To understand how a reversing dynamo would affect basin fields, here we model the cooling and magnetization of 200-2200 km diameter impact basins under a range of Earth-like reversal frequencies. We find that magnetic reversals efficiently reduce field strengths above large basins. In particular, if the magnetic properties of the Martian mantle are similar to most Martian meteorites and late remagnetization of the near surface is widespread, >90% of large ( > 800 km diameter) basins would appear demagnetized at spacecraft altitudes. This ultimately implies that Mars’s apparently demagnetized basins do not require an early dynamo cessation. A long-lived and reversing dynamo, unlike alternative scenarios, satisfies all available constraints on Mars’s magnetic history. Weak magnetic fields above Mars’s large impact basins are often interpreted as a signature of the dynamo’s early cessation. Here, the authors demonstrate that these weakly magnetic basins may instead have formed in a long-lived but reversing dynamo.

Impact-induced mixing between bolide and target is fundamental to the geochemical evolution of a growing planet, yet aside from local mixing due to jetting – associated with large angles of incidence between impacting surfaces – mixing during planetary impacts is poorly understood. Here we describe a dynamic instability of the surface between impacting materials, showing that a region of mixing grows between two media having even minimal initial topography. This additional cause of impact-induced mixing is related to Richtmyer-Meshkov instability (RMI), and results from pressure perturbations amplified by shock-wave refraction through the corrugated interface between impactor and target. However, unlike RMI, this new impact-induced instability appears even if the bodies are made of the same material. Hydrocode simulations illustrate the growth of this mixing zone for planetary impacts, and predict results suitable for experimental validation in the laboratory. This form of impact mixing may be relevant to the formation of stony-iron and other meteorites. The authors describe a dynamic surface instability between impacting materials, showing that a region of mixing grows between two media. The study implies that this can explain mixed compositions and textures in certain meteorites.

Background Emergency and essential surgical, obstetric and anaesthesia (SOA) care are now recognized components of universal health coverage, necessary for a functional health system. To improve surgical care at a national level, strategic planning addressing the six domains of a surgical system is needed. This paper details a process for development of a national surgical, obstetric and anaesthesia plan (NSOAP) based on the experiences of frontline providers, Ministry of Health officials, WHO leaders, and consultants. Methods Development of a NSOAP involves eight key steps: Ministry support and ownership; situation analysis and baseline assessments; stakeholder engagement and priority setting; drafting and validation; monitoring and evaluation; costing; governance; and implementation. Drafting a NSOAP involves defining the current gaps in care, synthesizing and prioritizing solutions, and providing an implementation and monitoring plan with a projected cost for the six domains of a surgical system: infrastructure, service delivery, workforce, information management, finance and governance. Results To date, four countries have completed NSOAPs and 23 more have committed to development. Lessons learned from these previous NSOAP processes are described in detail. Conclusion There is global movement to address the burden of surgical disease, improving quality and access to SOA care. The development of a strategic plan to address gaps across the SOA system systematically is a critical first step to ensuring countrywide scale‐up of surgical system‐strengthening activities. Antecedentes En la actualidad, se reconoce que la atención quirúrgica, obstétrica y anestésica urgente y esencial (surgical, obstetric, and anaesthesia, SOA) es uno de los componentes de la cobertura sanitaria universal y un elemento necesario para el funcionamiento de un sistema de salud. Para mejorar la atención quirúrgica a nivel nacional, se necesita una planificación estratégica que aborde los seis dominios de un sistema quirúrgico. En este artículo, se detalla el proceso para el desarrollo de un plan nacional de cirugía, obstetricia y anestesia (national surgical, obstetric, and anaesthesia plan, NSOAP) basado en las experiencias de los principales proveedores, los funcionarios del Ministerio de Salud, los líderes de la Organización Mundial de la Salud y consultores. Métodos El desarrollo de un NSOAP incluye ocho pasos clave: (1) apoyo y dependencia del ministerio, (2) análisis de la situación y evaluaciones de referencia, (3) compromiso de los agentes implicados y establecimiento de prioridades, (4) redacción y validación, (5) seguimiento y evaluación, (6) análisis de costes, (7) gobernanza y (8) implementación. Redactar un NSOAP implica definir los déficits actuales en la atención, sintetizar y priorizar soluciones, y proporcionar un plan de implementación y seguimiento con unos costes proyectados para los seis dominios de un sistema quirúrgico: infraestructura, prestación de servicios, personal, gestión de la información, finanzas y gobernanza. Resultados Hasta la fecha, cuatro países han completado un NSOAP y 23 más se han comprometido con su desarrollo. Las lecciones aprendidas de estos procesos previos de NSOAP se describen con detalle. Conclusiones Existe un movimiento global para abordar la carga de las enfermedades que precisan cirugía, mejorar la calidad y el acceso a la atención SOA. El desarrollo de un plan estratégico para la aproximación sistemáticamente los déficits en todo el sistema SOA es un primer paso crítico para garantizar la ampliación a nivel nacional de las actividades de fortalecimiento del sistema quirúrgico. This article describes a possible skeleton process for developing a national surgical, obstetric and anaesthesia plan (NSOAP) from the authors' experiences of developing some of the world's first NSOAPs in low‐ and middle‐income countries. It discusses the specific challenges encountered and highlights lessons learned from navigating this process. Reproducible framework for improving global surgical care

Born in Cape Town in 1951, Neil David Citron began his training at Trinity College, Cambridge, before moving to University College Hospital, London, to graduate in 1975. A keen violinist, a dependable attendee at hospital committee meetings, and the chair of a charity supporting an Israeli hospital which treats patients of any ethnic group, he was generous with both his time and his talents.

Impacts may have had a significant effect on the atmospheric chemistry of the early Earth. Reduced phases in the impactor (e.g., metallic iron) can reduce the planet's H\\(_2\\)O inventory to produce massive atmospheres rich in H\\(_2\\). Whilst previous studies have focused on the interactions between the impactor and atmosphere in such scenarios, we investigate two further effects, 1) the distribution of the impactor's iron inventory during impact between the target interior, target atmosphere, and escaping the target, and 2) interactions between the post-impact atmosphere and the impact-generated melt phase. We find that these two effects can potentially counterbalance each other, with the melt-atmosphere interactions acting to restore reducing power to the atmosphere that was initially accreted by the melt phase. For a \\(\\sim10^{22}\\,\\mathrm{kg}\\) impactor, when the iron accreted by the melt phase is fully available to reduce this melt, we find an equilibrium atmosphere with H\\(_2\\) column density \\(\\sim10^4\\,\\mathrm{moles\\,cm^{-2}}\\) (\\(p\\mathrm{H2}\\sim120\\,\\mathrm{bars}\\mathrm{,}~X_\\mathrm{H2}\\sim0.77\\)), consistent with previous estimates. However, when the iron is not available to reduce the melt (e.g., sinking out in large diameter blobs), we find significantly less H\\(_2\\) (\\(7\\times10^2-5\\times10^3\\,\\mathrm{moles\\,cm^{-2}}\\), \\(p\\mathrm{H2}\\lesssim60\\,\\mathrm{bars}\\mathrm{,}~X_\\mathrm{H2}\\lesssim0.41\\)). These lower H\\(_2\\) abundances are sufficiently high that species important to prebiotic chemistry can form (e.g., NH3, HCN), but sufficiently low that the greenhouse heating effects associated with highly reducing atmospheres, which are problematic to such chemistry, are suppressed. The manner in which iron is accreted by the impact-generated melt phase is critical in determining the reducing power of the atmosphere and re-solidified melt pool in the aftermath of impact.

The ancient crust of Mars contains a remarkable record of the planet's early history. With 45% of the martian crust dated to the Noachian (>3.7 Ga) and another 30% of the crust dated to the Hesperian (>3 Ga), Mars provides a unique opportunity to examine processes that can influence the early evolution of terrestrial planets. Observations of Mars' surface motivate hypotheses as to what processes controlled the planet's early evolution and how the surface developed into its present form. Key features to explain for early Mars are the formation of the crustal dichotomy, the massive Tharsis volcanic province, and the prevalence of features indicating widespread early water. Hypotheses for the formation of these features can be tested using geodynamic models. For the origin of the crustal dichotomy, both endogenic (mantle convection) and exogenic (giant impact) mechanisms have been proposed. We examine if a hybrid model in which a giant impact can influence the global pattern of mantle convection. We find that a superplume can form on Mars following an early giant impact, and examine the subsequent superplume dynamics and migration in relation to the formation of Tharsis and remanent crustal magnetism. For a purely giant impact origin of the crustal dichotomy, we find that the crustal structure of the dichotomy is difficult to reproduce with high-resolution impact models. We also examine evidence for early oceans on Mars, finding that deviations in proposed paleoshoreline elevations from present-day equipotential surfaces can be explained by deformation due to the emplacement of Tharsis and other surface loads. Our results suggest that Mars paleoshorelines follow paleo-equipotentials, supporting the ocean hypothesis. Overall, our results provide insight into the early processes that may have occurred on Mars, and their effect on the subsequent evolution of the planet.

Late accretion onto the Hadean Earth included large impacts that could have influenced early habitability, either by sterilizing the planet or alternatively catalyzing the origin of life by delivering iron required to create a reducing environment/atmosphere. We present 3D numerical simulations of 1500-3400 km diameter impacts on the early Earth in order to quantify their effects on planetary habitability. We find sterilizing impact events require larger projectiles than previously assumed, with a 2000-2700 km diameter impactor required to completely melt Earth's surface and an extrapolated >700 km diameter impactor required for ocean-vaporization. We also find that reducing environments are less likely to arise following large impacts than previously suggested, because >70% of the projectile iron is deposited in the crust and upper mantle where it is not immediately available to reduce surface water and contribute to forming a reducing atmosphere. Although the largest expected late accretion impacts (~1 lunar mass) delivered sufficient iron to the atmosphere to have reduced an entire ocean mass of water, such impacts would also have melted the entire surface, potentially sequestering condensing iron that is not oxidized quickly. The hypothesis that life emerged in the aftermath of large impacts requires an efficient mechanism of harnessing the reducing power of iron sequestered in the crust/mantle, or an origin of life pathway that operates in more weakly-reducing post-impact environments that require smaller quantities of impact-delivered iron.

The recovery of freshly fallen meteorites from tracked and triangulated meteors is critical to determining their source asteroid families. However, locating meteorite fragments in strewn fields remains a challenge with very few meteorites being recovered from the meteors triangulated in past and ongoing meteor camera networks. We examined if locating meteorites can be automated using machine learning and an autonomous drone. Drones can be programmed to fly a grid search pattern and take systematic pictures of the ground over a large survey area. Those images can be analyzed using a machine learning classifier to identify meteorites in the field among many other features. Here, we describe a proof-of-concept meteorite classifier that deploys off-line a combination of different convolution neural networks to recognize meteorites from images taken by drones in the field. The system was implemented in a conceptual drone setup and tested in the suspected strewn field of a recent meteorite fall near Walker Lake, Nevada.