Counter-intuitive links between cave genesis and subaerial stream dynamics in the Têt valley–Lachambre network, eastern Pyrénées, France

International audienceThe Lachambre cave network (Eastern Pyrenees, France) is well suited to studying the interaction between vertical successions of low-gradient cave passages in the limestone and chronosequences of fluvial terraces in the adjacent valley. Investigations here focus on cave passages striking parallel to the Têt River, and on their topographic, geomorphological, sedimentological and geochronological relationship with the two youngest generations of Pleistocene fluvial terrace, T2 and T1. Results reveal that the longitudinal profiles of the terraces and modern thalweg (1.5–3%) are ten times steeper than the profiles of the subterranean passages (0.1–0.3%), which display typical characteristics of water table caves. The respective cave and fluvial terrace profiles consequently diverge scissor-like on either side of a point of intersection, with the elevation of cave levels upstream occurring below the elevation of comparatively younger terrace treads, and even below the modern thalweg. U/Th ages obtained from speleothems and previously published 26Al/10Be burial ages of quartz-rich sediment indicate that the downstream segment of the cave passage (i) formed during Marine Isotope Stage 6, (ii) was invaded soon after by a subterranean debris cone (at times of fluvial aggradation in the Têt catchment, cones of river bedload entered the caves through valleyside sinkholes), (iii) was partially filled by an influx of gravel from upstream during MIS 4, (iv) experienced speleothem growth during MIS 3, and (v) underwent further geomorphic changes during MIS 2. Such complicated interactions between subaerial and subterranean dynamics emphasize the necessity for caution when using caves as tools for quantifying valley incision by rivers – particularly when using them as substitutes for fluvial terraces in widespread situations where none are available. Cave altimetry, speleogen inventories, cross-cutting relations in cave sediment stratigraphy and age-bracketing of fluvial deposits and speleothems all contribute to elaborating a more accurate understanding of how cave development interrelates with Quaternary alluvial cycles

High-energy neutrino transients and the future of multi-messenger astronomy

International audienceThe recent discovery of high-energy astrophysical neutrinos and first hints of coincident electromagnetic and neutrino emission herald the beginning of the era of multi-messenger astronomy. Due to their high power, transient sources are expected to supply a significant fraction of the observed energetic astroparticles, through enhanced particle acceleration and interactions. Here, we review theoretical expectations of neutrino emission from transient astrophysical sources and the current and upcoming experimental landscape, highlighting the most promising channels for discovery and specifying their detectability

Theia: Faint objects in motion or the new astrometry frontier

International audienceIn the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 $\%$ of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision

Mars as a Planet B?

International audienceThe concept of terraforming Mars has been popularized in pop culture and recently by Elon Musk. The objective is to transform Mars into a planet suitable for habitation by living organisms and humans. Conceptually, this may be achieved in different steps: firstly, by increasing the atmospheric pressure of the whole planet to allow human beings to perform outdoor activities, possibly equipped with only an oxygen mask and without a pressurized suit. Secondly, by transforming the environment to make terrestrial organisms able to survive and proliferate. Thirdly, by creating a breathable atmosphere. The process would require a strong thickening of the atmosphere. A method to restore the early Mars CO2 atmosphere had been hypothesized in the 1990s, but after 30 years of Mars exploration, its feasibility is strongly questioned. Even if terraforming became possible, implementing it would violate many principles of modern environmental ethics. Assuming it is done for the purpose of habitation, it would also raise many legal and societal issues, pertaining notably to the relationships between communities on Mars and the Earth’s populations, structures, and rules

Evaluation of three modelling frameworks of thermal infrared radiative transfer for directional anisotropies of temperatures

International audienceRadiative transfer models (RTMs) designed to reproduce the anisotropy of surface brightness temperature are particularly useful for applications on Earth’s energy budget when using remote sensing data sets. Despite the fact that several thermal infrared (TIR) RTMs have been developed, a quantitative analysis comparing the benefits and limits of these models remains necessary. Herein, three modeling frameworks (physical hybrid, analytical parameterization, kernel-driven) have been evaluated comparatively for a homogeneous vegetation, a row-planted crop and a sparse forest. Airborne measurements and the Discrete Anisotropy Radiative Transfer (DART) model simulations were retained as the benchmark. Forward modeling and inverse fitting schemes were proposed for the sake of comparison. Results reveal that: 1) in the forward modeling scheme, from airborne measurements, the hybrid model performs better with RMSEs of 0.17℃, 1.57℃, and 0.38℃ for homogenous, row-planted vineyard and sparse forest scenes, respectively; the analytical model appears similar performant (0.17℃, 0.40 ℃) for the homogeneous and sparse forest scenes, but less performant (2.39℃) for the row-planted scene; 2) In the inverse fitting scheme, the uncertainties (95% of probability) of model coefficients and predicted directional anisotropies were considered. The kernel-driven model has fewer modeling constraints and statistically performs better for the homogeneous and sparse forest scenes with RMSEs of 0.07 ℃ and 0.19 ℃, respectively whereas it is less efficient for the row-planted scene with RMSE of 0.80 ℃. This study highlights the differences of accuracy between models of different complexity, and provides reference information for researchers to improve existing models and for users to choose their best modeling solution

Spectroscopic approach to chlorine local environment in aluminoborosilicate glasses

International audienceChlorine local environment has been investigated using spectroscopic approach (XAS and XPS) for Na-and Ca-bearing aluminoborosilicate glasses synthesised at 1.0 GPa. Based on Cl K-edge EXAFS results, Cl appears to show two local environments in glasses: one at long distance ~2.7 Å assigned to Cl -species charge compensated by Na + and/or Ca 2+ and one at short distance ~1.8 Å assigned to Cl-Cl and Si-Cl species. The Cl 2p XPS results cannot unambiguously confirm the presence of Si-Cl overlapped with Na + /Ca 2+ …Cl -species

Foreshock Ultralow Frequency Waves at Mars: Consequence on the Particle Acceleration Mechanisms at the Martian Bow Shock

International audienceUsing Mars Atmosphere and Volatile EvolutioN Magnetometer observations, we report the first statistical study of ultralow frequency (ULF) waves at the Martian foreshock. The analyzed foreshock ULF wave events are observed in the 0.008-0.086 Hz frequency range, with nearly circular and elliptical left-handed polarization in the spacecraft reference frame. These waves are propagated quasi-parallel to the ambient magnetic field, with a moderate wave amplitude. All these properties are consistent with fast magnetosonic waves, most likely generated through the ion-ion right-hand resonant instability. In addition, our results suggest that the associated resonant backstreaming protons' velocities parallel to the mean magnetic field in the solar wind reference frame are 1.33 ± 0.40 times the solar wind velocity. The similarity between our results and previous reports at other foreshocks may indicate the presence of a common acceleration process acting in planetary bow shocks and that is responsible for this particular backstreaming population.</div

Control Mechanisms for Self-Sealing in Activated Clay-Rich Faults Through Controlled Hydraulic Injection Experiment

International audienceIn a high-pressure injection fault activation experiment conducted at the Mont Terri underground research laboratory in Switzerland, the transmissivity of the Opalinus Clay fault significantly increased due to opening and shearing. The fluid injection, spanning a few hours, generated a 10 m radius fault activation patch. Subsequent pressure pulse tests conducted bi-weekly for a year revealed the gradual return of fault transmissivity to its initial state. The study utilized fluid pressure decay analysis, optical fiber monitoring, continuous active source seismic measurements and borehole displacement sensors for measuring fault displacements. The fault zone exhibited a dilation of approximately 1.4 mm, associated with both normal and tangential movements during activation, resulting in a sudden transmissivity increase from 1 × 10 12 to 3.2 × 10 7 m 2 /s. Early post-activation, transient compaction and the subsequent slow compaction were observed, transitioning to an extension regime. The pressure pulse tests demonstrated a rapid transmissivity drop by more than two orders of magnitude within the first 10 days, followed by a gradual and less pronounced decrease. Plastic shear and compaction dominated the transmissivity evolution until 70 days after injection ended, followed by a period where additional factors, such as clay mineral swelling, influenced the behavior. Extrapolation suggested a sealing process taking at least 50 years after the initial activation.Plain Language Summary A field-scale fault activation experiment offers valuable insights into the elasto-plastic processes governing the sealing of shale faults. The experiment reveals a rapid increase in the fault's transmissivity by approximately five orders of magnitude during activation. Subsequent observations show a gradual transmissivity decrease by about three orders of magnitude post-activation, with slow long-term plastic shear and compaction of the fault competing against secondary processes, notably clay mineral swelling. All conceptual models employed to interpret these field data converge on the estimation that the fault's return to its initial low transmissivity state would require a minimum of 50 years.</div

Euclid Quick Data Release (Q1). First detections from the galaxy cluster workflow

International audienceThe first survey data release by the Euclid mission covers approximately $63\,\mathrm{deg^2}$ in the Euclid Deep Fields to the same depth as the Euclid Wide Survey. This paper showcases, for the first time, the performance of cluster finders on Euclid data and presents examples of validated clusters in the Quick Release 1 (Q1) imaging data. We identify clusters using two algorithms (AMICO and PZWav) implemented in the Euclid cluster-detection pipeline. We explore the internal consistency of detections from the two codes, and cross-match detections with known clusters from other surveys using external multi-wavelength and spectroscopic data sets. This enables assessment of the Euclid photometric redshift accuracy and also of systematics such as mis-centring between the optical cluster centre and centres based on X-ray and/or Sunyaev--Zeldovich observations. We report 426 joint PZWav and AMICO-detected clusters with high signal-to-noise ratios over the full Q1 area in the redshift range $0.2 \leq z \leq 1.5$. The chosen redshift and signal-to-noise thresholds are motivated by the photometric quality of the early Euclid data. We provide richness estimates for each of the Euclid-detected clusters and show its correlation with various external cluster mass proxies. Out of the full sample, 77 systems are potentially new to the literature. Overall, the Q1 cluster catalogue demonstrates a successful validation of the workflow ahead of the Euclid Data Release 1, based on the consistency of internal and external properties of Euclid-detected clusters

Euclid Quick Data Release (Q1). The first catalogue of strong-lensing galaxy clusters

International audienceWe present the first catalogue of strong lensing galaxy clusters identified in the Euclid Quick Release 1 observations (covering $63.1\,\mathrm{deg^2}$). This catalogue is the result of the visual inspection of 1260 cluster fields. Each galaxy cluster was ranked with a probability, $\mathcal{P}_{\mathrm{lens}}$, based on the number and plausibility of the identified strong lensing features. Specifically, we identified 83 gravitational lenses with $\mathcal{P}_{\mathrm{lens}}>0.5$, of which 14 have $\mathcal{P}_{\mathrm{lens}}=1$, and clearly exhibiting secure strong lensing features, such as giant tangential and radial arcs, and multiple images. Considering the measured number density of lensing galaxy clusters, approximately $0.3\,\mathrm{deg}^{-2}$ for $\mathcal{P}_{\mathrm{lens}}>0.9$, we predict that \Euclid will likely see more than 4500 strong lensing clusters over the course of the mission. Notably, only three of the identified cluster-scale lenses had been previously observed from space. Thus, \Euclid has provided the first high-resolution imaging for the remaining $80$ galaxy cluster lenses, including those with the highest probability. The identified strong lensing features will be used for training deep-learning models for identifying gravitational arcs and multiple images automatically in \Euclid observations. This study confirms the huge potential of \Euclid for finding new strong lensing clusters, enabling exciting new discoveries on the nature of dark matter and dark energy and the study of the high-redshift Universe