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Stratigraphy of Carbonate‐Bearing Rocks at the Margin of Jezero Crater, Mars: Evidence for Shoreline Processes?
No full textInternational audienceMartian carbonate‐bearing rocks are compelling targets for exploration because they preserve detailed records of past aqueous processes, climate, and habitability. The Margin unit in Jezero crater is a distinct olivine‐ and carbonate‐bearing unit stratigraphically underlying the western fan, lining the inner margin of the western crater rim and has a contested origin. Perseverance spent ∼350 sols investigating the unit as part of its fourth mission campaign, aiming to constrain its origin, alteration history and biosignature preservation potential. This study reports on the lithofacies and stratigraphy of the unit by analyzing Mastcam‐Z mosaics and derived 3D outcrop models, supplemented by long‐distance SuperCam observations and detailed textural analyses from SHERLOC WATSON and ACI images. We find that the Margin unit comprises two distinct subunits. The Eastern Margin Unit (EMU) comprises well‐stratified, low‐angle basinward‐, rimward‐ and subhorizontally inclined medium‐grained sandstones which preserve angular to rounded grains, occasional crossstratification, convex‐up bedding, and erosion surfaces. The Western Margin Unit (WMU) comprises distinctly structureless to decimeter‐scale parallel‐layered rocks which drape the crater rim and are inclined into the crater. The origin of the WMU is uncertain but may be most consistent with a variably carbonated olivine cumulate. The favored depositional model for the EMU is a lacustrine shore zone environment where sediments derived from the adjacent WMU have been locally reworked by wave action along a paleoshoreline at around –2,400 m elevation. These observations suggest that the Margin unit preserves diverse subsurface and surface aqueous environments and further extends the habitability window at Jezero crater
A Hierarchy of Turbulence Closure Model For the Turbulent Atmospheric boundary Layers: A Formal Derivation with Nondimensionalization and the Anisotropy Parameter by
No full textAql X-1 from dawn 'til dusk: the early rise, fast state transition and decay of its 2024 outburst
No full textInternational audienceTransient Low-Mass X-ray Binaries (LMXBs) are usually first detected by all-sky X-ray monitors when they enter new outbursts, typically at X-ray luminosities above 10 erg/s. Observations of these sources during the early rise of the outbursts have so far been very limited. However, the launch of the Einstein Probe (EP) has greatly improved our ability to detect fainter X-ray activity, unlocking access to the outburst early rise. In September 2024, EP detected the early onset of a new outburst from the neutron star LMXB Aql X-1, catching the source at a luminosity below 10 erg/s. In this paper we present results from a comprehensive, multi-wavelength campaign of this event, combining data from EP, NICER, NuSTAR, Swift and Las Cumbres Observatory covering the full outburst from its early rise through its decay. By comparing X-ray and optical light curves obtained with Las Cumbres Observatory during the initial rise, we show that the start of the X-ray emission lagged the optical rise by, at most, 3 days. Time-resolved X-ray spectroscopy revealed how the geometry and the physical properties of the accretion flow evolve during this early stage of the outburst, as well as at higher luminosities as the source transitioned through the canonical X-ray spectral states - hard, intermediate and soft. These data show that the source underwent a very rapid, about 12-h long, transition from the hard to the soft state about two weeks after the optical onset of the outburst. The evolution of the temperature and physical sizes of both the inner region of the disk and a black body near the NS surface suggest that at the state transition, a boundary and spreading layer likely formed. We discuss these results in the context of time-scales for outburst evolution and state transitions in accreting neutron stars and black holes
The LISA Astrophysics "Disc-IMRI" Code Comparison Project: Intermediate-Mass-Ratio Binaries in AGN-Like Discs
No full textInternational audienceUpcoming space-based gravitational wave detectors such as LISA, the Laser Interferometer Space Antenna, will be sensitive to extreme- and intermediate-mass-ratio inspirals (EMRIs and IMRIs). These binaries are comprised of a supermassive black hole and a stellar-mass object or intermediate-mass black hole. Their detection will probe the structure of galactic nuclei and enable tests of general relativity. As these events will be observed over thousands of orbital cycles, they will be extremely sensitive to both the underlying spacetime and astrophysical environment, demanding exquisite theoretical models on both fronts to avoid biased or even erroneous results. In particular, many (E/)IMRIs are expected to occur within accretion discs around supermassive black holes, and the nonlinearities present when modeling these systems require numerical simulations. In preparation for future modeling of LISA sources, we have conducted a comparison between eight different hydrodynamical codes and applied them to the problem of a q = 10^{-4} mass ratio binary interacting with an accretion disc. Thicker discs appear more lenient, and all codes at sufficiently high resolutions are in good agreement with each other and analytical predictions. For thinner discs, beyond the reach of analytical models, we find substantial disagreement between 2D and 3D simulations and between different codes, including both the magnitude and sign of the torque. With time and energy efficiency in mind, codes that leverage moving meshes or grid-based Lagrangian remapping seem preferable, as do codes that can leverage graphical processing units and other energy-efficient hardware
Neutron star heating vs. HST observations
No full textInternational audiencePassively cooling neutron stars (NSs) should reach undetectably low surface temperatures K in less than yr. However, HST observations have revealed likely thermal UV emission from the Gyr-old millisecond pulsars PSR~J04374715 and PSR~J21243358, and from the yr-old classical pulsars PSR~B095008 and PSR~J01081431, implying K and the need for heating mechanisms. We compute the thermal evolution of these NSs including rotochemical heating (RH) in the core with normal or Cooper-paired matter, vortex creep (VC) in the inner crust, and crustal heating through nuclear reactions, and compare the results with observations and with the upper limit for PSR~21443933. No single mechanism explains all sources. The high temperature of PSR~J04374715 can be reproduced by RH with a large Cooper pairing gap MeV for either neutrons or protons, but this requires an unrealistically short initial period ms to activate the same mechanism in PSR~B095008. Conversely, the latter can be explained by RH with modified Urca reactions in normal matter or by VC with an excess angular momentum erg,s, but these models underpredict PSR~J04374715. A model combining RH with a large pairing gap and VC matches both pulsars and is consistent with the upper limits for the remaining three. It further predicts that their temperatures should lie close to these limits, suggesting that deeper or broader-wavelength observations would provide a strong test of this scenario
A glitch in the millisecond pulsar J09003144
No full textInternational audienceWe report the detection of a glitch in the millisecond pulsar (MSP) PSR J09003144, which is included in the European, MeerKAT and Parkes pulsar timing array experiments. The dataset combines observations from the MeerKAT, Nançay, Lovell, and Murriyang telescopes, spanning a total baseline of approximately 14 years. The glitch occurred on MJD~59942(17), with a measured fractional spin frequency step of . This event represents the third glitch detected in a MSP, following those in PSRs B182124A and J06130200. Although smaller in amplitude than the previous two, the glitch in PSR J09003144 is of a comparable order of magnitude. The updated MSP glitch rate is glitches per pulsar per year, which suggests it is likely current PTAs will detect another MSP glitch within five years. Using simulations, we demonstrate that such small glitches can go undetected, especially in short datasets such as those from new PTAs, and can bias the inferred achromatic noise model parameters, potentially leading to the down-weighting of the pulsar in gravitational wave background searches
Is the high-energy environment of K2-18b special?
No full textInternational audienceK2-18b lies near the radius valley that separates super-Earths and sub-Neptunes, marking a key transitional regime in planetary and atmospheric composition. The system offers a valuable opportunity to study how M-dwarf high-energy stellar radiation influences atmospheric stability and the potential for sustaining volatile species, especially important in the context of the upcoming ELT and its ANDES spectrograph. This study characterizes the high-energy environment of K2-18 with X-ray observations from eROSITA, the soft X-ray instrument on the Spectrum-Roentgen-Gamma (SRG) mission, Chandra, and XMM-Newton. We derive a representative 0.2-2 keV X-ray flux with an APEC thermal plasma model fitted with the Bayesian X-ray Analysis (BXA). With the observed X-ray flux from the exoplanet host star, we estimate the photo-evaporation mass loss of exoplanet K2-18b using the energy-limited model. In addition, we examine the thermal structure of the system based on a hydrodynamic model. In 100 ks XMM-Newton observations we identified K2-18 as a very faint X-ray source with , with an activity level of (Lx/Lbol) . A small flare has been detected during the observation. The planet is irradiated by an X-ray flux of . The X-ray flux measurement of K2-18 gives important limitations for atmospheric escape and photochemical modeling of its exoplanets. Despite its near orbit around an M-dwarf star, K2-18b's low activity level environment suggests that it can retain an atmosphere, supporting recent tentative detections of atmospheres
On the performance of radiocarbon and quartz OSL dating in macrotidal estuarine environments: Four case studies from Western France
No full textInternational audienceThe study of estuarine sedimentary archives provides valuable insights into their geomorphological evolution over the past two centuries, enhancing our understanding of estuarine responses to climate change. Establishing a reliable and precise geochronological framework is therefore essential for monitoring these changes. This study evaluates the performance of quartz Single-Aliquot Regenerative (SAR) OSL and AMS 14C dating in four estuaries along the western coast of France. The results are compared with cartographic data, serving as an independent age control. Of the 14 OSL dated samples, 10 yield depositional ages consistent with cartographic data, whereas the remaining 4 appear to overestimate ages by 20–100 years. In contrast, AMS 14C dating reveals numerous stratigraphic inversions, with at least 12 out of the 16 measured samples overestimating the depositional age in some cases by up to 5000 years, in total disagreement with cartographic data. The discrepancy between the OSL and radiocarbon ages reflects the constant reworking of allochthonous material, to which is added the further uncertainty associated with the local reservoir age. These factors fundamentally limit the reliability of 14C dating regardless of the material analyzed. By contrast, the OSL signal displays remarkable resilience, with any age overestimation linked to partial bleaching remaining minor (on the order of decades) compared with the errors affecting 14C ages. This underscores the capacity of OSL dating to resolve short-term environmental changes and positions it as the most reliable tool for constructing high-resolution chronologies of the last centuries in macrotidal estuarine settings
Long-duration in situ monitoring of H2O and CH4 in the equatorial tropopause with the Pico-STRAT Bi Gaz balloon borne laser diode spectrometer during the Strateole 2 campaign
No full textInternational audienceThe Pico-STRAT Bi Gaz spectrometer provides in situ mixing ratio measurements of H2O and CH4 (or CO2 ) under balloon. The instrument was flown in the tropical upper troposphere and lower stratosphere in 2019/2020 and 2021/2022 during the Strateole 2 campaigns for a total of five flights of 20 to 80 days between 18 and 20 km altitude. In this frame, in situ measurements of water vapor and methane were performed every 4 to 12 minutes in the equatorial tropopause layer. On several occasions, water vapor measurements of Pico-STRAT Bi Gaz have been compared with localized measurements from the FLASH-B Lyman-α hygrometer and vertical profiles of the NOAA Global Monitoring Laboratory (GML) frost point hygrometer over Hilo, Hawaii. Pico-STRAT Bi Gaz measurements agreed with the FLASH-B hygrometer to within 2.2 ± 5.3 % between 18.2 and 18.7 km in 2021 and to within 1.3 ± 5.3 % near 19 km in December 2019. Pico-STRAT Bi Gaz agreed with NOAA’s FPH hygrometer to within 1.2 ± 4.1% between 18 and 19 km on four occasions during the two campaigns. These are within both instruments’ uncertainties. Methane measurements from Pico-STRAT Bi Gaz have been compared with in situ measurements from the Whole Air Sampler instrument (WAS), flown aboard the NASA WB-57 aircraft during the ACCLIP 2022 campaign over South Korea, eight months after the Pico-STRAT Bi Gaz overpass. The relative difference between both instruments is found to be of (−0.1 ± 0.9) % within the altitude range from 17 to 19 km and within the Pico-STRAT measurement uncertainty
Oceanographic and hydroclimatic data explain depressed water level in the coastal karst hosting the decorated Paleolithic Cosquer cave (France)
No full textInternational audiencePaleolithic decorated caves are home to a priceless heritage, but their preservation depends on hydroclimatic conditions within the cave. In coastal areas, changing sea levels pose a further threat to caves, as the sea floods the karst and obliterates Paleolithic artefacts. In this paper, we study the case of the Cosquer Cave, a half-submerged coastal cave located in southeastern France, home to Upper Paleolithic archeological remains. This is a very special case, where the sea represents both an opportunity and a threat for the preservation of an archeological site. The cave is confined, submerged in its lower part, and embedded in a limestone massif with low permeability in the unsaturated zone. Several times a year, mainly in autumn, winter, and spring, air flows through the karstic massif, most likely below sea level, raising the cave's air pressure above atmospheric pressure. The resulting overpressure lowers the cave water level for weeks, keeping it below sea level and temporarily keeping the lowest wall paintings and engravings emerged. However, the oceanographic conditions that cause a pressurization event have not yet been described, although it is a key understanding to help preserve the natural heritage housed in the Cosquer Cave. Based on nine years of in situ continuous monitoring, we use descriptive statistics to decipher the oceanographic conditions controlling air inflow, air outflow, and absence of air flow through the submerged karst. We show that waves are the engine for the pressurization of the cave. The three main factors controlling air entrance are wave height, wave direction and seawater level. 90 % of air inflows coincide with significant wave heights exceeding 0.8 m. Additionally, air inflows are more efficiently caused by SSW and SW waves, propagating in a direction orthogonal to the cliff than by waves from the SE-SSE direction, propagating along the cliff. The minimum wave height required for air inflow to occur increases with sea-level rise, likely because submerged conduits become less accessible for air input. This study establishes a conceptual model of functioning for the natural hydrosystem of the Cosquer Cave, and provides the basis for further modeling and predictions according to scenarios of climate change and sea-level rise