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Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering?
No full textInternational audienceBased on observation and data from meteorites and in situ scientific missions, experiments as well as models, the Martian mantle is assumed to share some compositional and mineralogical affinity with the terrestrial mantle. However, there might be subtle differences like the Martian mantle being more ferroan. Yet, we do not have any direct analysis of a Martian mantle rock to confirm this assumption. NASA’s Perseverance rover found olivine-rich boulder-sized float rocks on the upper Jezero fan (Mars). These boulders have an ultramafic composition and their mineralogy is dominantly composed of Fo73±3 olivine with high-Mg orthopyroxene, Cr-rich Ti-Fe oxides and minor plagioclase and high-Ca pyroxene. Microtextural and petrological analysis reveals that these minerals crystallized at equilibrium. In addition, these boulders are different from all the bedrocks analyzed by Perseverance along its traverse which are crustal igneous rocks and sediments. Comparing our data to Martian meteorites and available Mars bulk silicate models (BSM), we discuss that these boulders could represent primitive melts and/or lower crustal material, and we specifically hypothesize that they could be mantle peridotites. We propose that these putative mantle rocks could have been excavated by the succession of impacts from the shallow mantle or lower crust in the Isidis region where Jezero crater is located. These olivine-rich boulders could thereby constitute the first direct analysis of a Martian mantle rock
Synchronous Miocene radiations and geographic-dependent diversification of pantropical Xylopia (Annonaceae).
No full textInternational audienc
Inundation flow velocities generated by tropical cyclones across atoll islands, derived from two centuries of megaclast deposits in French Polynesia
No full textInternational audienceUnderstanding potential flow velocities during high-energy marine inundation events is crucial for coastal risk assessment. However, modelling struggles to simulate wave energy dissipation across atoll island coastlines. Here, we examined coral reefblocks transported by past tropical cyclones to calculate the minimum flow velocities (MFVs) responsible. Fieldwork on 6 atolls in the Tuamotu archipelago (South Pacific) examined 196 reefblocks, some megaclasts exceeding 300 cubic metres in size. These blocks are scattered between the oceanside reef edge and the atoll lagoon over several hundred metres and suggest flow velocities much higher than those modelled in an assumed ‘extreme reference scenario’ (HS = 12 m). Through U/Th dating and by studying archives and historical aerial photos, the cyclones that moved these reefblocks were identified. Inundation flows generated by two recent cyclones (March and April 1983), two historical cyclones (1903 AD and 1906 AD) and one prehistorical cyclone (54–80 AD) were calculated (storms with swells 10–18.5 m in height). Calculations reveal that previous modelling underestimates flow velocities across atoll islands (inhabited areas) for two reasons: the underestimation of extreme swell heights and the unaccounted-for degradation of shoreline rubble ramparts. During a supercyclone (HS > 15 m), flows can exceed 3 m/s at 350 m from the reef edge and are capable of transporting 20-ton coral blocks. Findings have a wider significance to tropical coral reef coastlines beyond these atolls studied, where the presence of reefblocks can allow hindcasting of the characteristics of prehistorical cyclone inundations
Density dependence of measured line intensities for O2 transitions
No full textInternational audienceWe report predictions and measurements of O2 absorption spectra that exhibit line intensity depletion with increasing gas density. This effect, which is attributed to the finite duration of collisions, alters the line shape by redistributing a portion of the intensity from a relatively narrow spectrum that can be described by an impact-approximation-based profile to a broad pedestal with a width that is inversely related to the collision duration. Using classical molecular dynamics simulations (CMDS), we predicted details regarding this mechanism for O2 with four collision partners: O2, N2, Ar, and He at a temperature of 296 K. These simulations were validated by comparisons with experimental intensity depletion coefficients obtained from absorption spectra of the 1.27 μm band of O2 in air; Ar and He acquired over a wide pressure range up to 120 kPa. All experimental spectra were recorded using high-precision cavity ring-down spectroscopy (CRDS) apparatuses at NIST (United States of America) and LIPhy (France). For air-broadened O2, more specifically, a mean depletion value of ∼0.3% amagat−1 was observed, with almost no resolvable rotational dependence. The temperature dependence of the intensity depletion in this system was also investigated by CMDS at 250 and 296 K and by CRDS spectra of air at 250, 275, and 296 K. The theoretical results suggest a nearly 1/T2 temperature dependence of the intensity-weighted depletion coefficient, which over the limited temperature range considered, was only slightly greater than the measurement precision. Finally, simulations of atmospheric solar absorption spectra were implemented to quantify the impact of neglecting this depletion effect on the retrieved surface pressure, resulting in a negatively biased measurement of ∼0.14%, with a spread of ∼0.02% caused by seasonal variations in gas temperature
A complete list of He-pressure-broadening coefficient of CO2 lines from 100 K to 3000 K for planet and exoplanet opacity calculations
No full textInternational audienceHe pressure-broadening coefficients of CO 2 lines were predicted over a wide temperature range (100-3000 K) using requantized classical molecular dynamics simulations (rCMDS). This approach, based on the use of an ab initio intermolecular interaction potential, Newtonian equations of motion, and a requantized procedure, enables the calculation of the spectral density of He-broadened CO 2 spectra. The resulting spectra were fitted with the usual Voigt profile to deduce He-broadening coefficients. Requantization was calibrated to match the rCMDS-predicted broadenings coefficients to quantum scattering results at room temperature, available for thirteen lines, computed with the same potential. Comparisons between rCMDS and quantum calculations at 123 K and 760 K showed very good agreements. Excellent agreements with experimental data were also observed at 123 K, 160 K, 565 K, and 760 K. rCMDS calculations were then extended to several temperatures up to 3000 K, enabling prediction of broadening coefficients for rotational quantum numbers up to J = 240, where no prior theoretical or experimental data exist. The temperature dependence of the broadening coefficients was then determined using either a double power-law model when applicable or the usual single power law. The resulting dataset provides He-broadening coefficients of CO 2 lines for J up to 166 for any temperature between 100 K and 3000 K. These results represent the most comprehensive set of line-shape parameters for CO 2 perturbed by He, providing improved input for spectroscopic databases and for opacity modeling in planetary and exoplanetary atmospheres
Encapsulating textual contents into a MOC data structure for advanced applications
No full textInternational audienceThe Multi-Order Coverage map (MOC) is a widely adopted standard promoted by the International Virtual Observatory Alliance (IVOA) to support data sharing and interoperability within the Virtual Observatory (VO) ecosystem. This hierarchical data structure efficiently encodes and visualizes irregularly shaped regions of the sky, enabling applications such as cross-matching large astronomical catalogs, visualizing multi-wavelength and multi-messenger surveys, and facilitating collaborative research through seamless interoperability in big-data-driven exploration. This study aims to explore potential enhancements to the MOC data structure by encapsulating textual descriptions and semantic embeddings into sky regions. Specifically, we introduce “Textual MOCs”, in which textual content is encapsulated, and “Semantic MOCs” that transform textual content into semantic embeddings. These enhancements are designed to enable advanced operations such as similarity searches and complex queries and to integrate with generative artificial intelligence (GenAI) tools to improve context-aware interactions and response accuracy in astronomical data analysis, and support agent-based applications. We experimented with Textual MOCs by annotating detailed descriptions directly into the MOC sky regions, enriching the maps with contextual information suitable for interactive learning tools. For Semantic MOCs, we converted the textual content into semantic embeddings, numerical representations capturing textual meanings in multidimensional spaces, and stored them in high-dimensional vector databases optimized for efficient retrieval. The implementation of Textual MOCs enhances user engagement by providing meaningful descriptions within sky regions, facilitating the development of effective game-based learning. Semantic MOCs enable sophisticated query capabilities, such as similarity-based searches and context-aware data retrieval, enhancing astronomical data analyses. Integration with multimodal generative AI systems allows for more accurate and contextually relevant interactions supporting both spatial, semantic and visual operations for advancing astronomical data analysis capabilities. Through straightforward examples, we discuss the fundamentals of this new experimental implementation
Rapidly rotating hot nuclear and hypernuclear compact stars: integral parameters and universal relations
No full textInternational audienceIn this work, we investigate hot, isentropic compact stars in the limiting cases of static and maximally rotating configurations, focusing on how variations in the symmetry energy of the equation of state derived from covariant density functional theory affect stellar properties. We consider both nucleonic and hyperonic matter with systematically varied symmetry energy slopes, fixed entropies per baryon and 3, and electron fractions and , representative of conditions in binary neutron star mergers and proto-neutron stars. We compute and analyze mass--radius and moment--of--inertia--mass relations, as well as the dependence of the Keplerian (mass-shedding) frequency on mass, angular momentum, and the ratio of kinetic to gravitational energy. Furthermore, we show that several universal relations between global properties remain valid across both nucleonic and hyperonic equations of state with varying symmetry energy, both in the static and Keplerian limit, and for various combinations of the fixed entropy and electron fraction
Surface albedo and thermal radiation dynamics under conservation and conventional agriculture in subhumid Zimbabwe
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/614360/) * Autres projets (id;sigle;titre): 101138269;ACCURATE;(EU) Albedo, Conservation agriCUltuRe and climATe bEnefit// FOOD/2021/424–933;RAIZ;(EU) Promoting agroecological intensification for resilience building in Zimbabwe//International audienceWhile conservation agriculture (CA) has been widely evaluated for its biogeochemical effects (e.g soil organic carbon sequestration and greenhouse gas emissions) for climate mitigation, its biogeophysical impacts related to changes in surface albedo remain understudied. This study assessed the biogeophysical effects of CA cropping systems with maize (Zea mays L.) in Zimbabwe. Measurements were conducted continuously over two cropping years at two long-term experiments with contrasting soil characteristics, on an abruptic Lixisol and on a xanthic Ferralsol. The dynamics of surface albedo, longwave radiation, leaf area index, soil moisture and temperature were monitored under three different treatments: conventional tillage (CT, tilled to ~15 cm), no-tillage (NT) and no-tillage with mulch (NTM, 2.5 t DM ha⁻¹). Our results revealed that, on the Ferralsol, NT and NTM significantly (p < 0.05) increased mean annual albedo (0.17) relative to CT (0.16), resulting in a negative instantaneous radiative forcing (iRF) and indicating a net cooling effect. iRF was stronger in 2021/22 (NT: -0.83 ± 0.17 W m-2; NTM: -1.43 ± 0.7 W m-2) than in 2022/23 (NT: -0.43 ± 0.09 W m-2; NTM: -1.03 ± 0.21 W m-2). Conversely, on the Lixisol, while NT increased surface albedo (0.27 vs. CT: 0.24), NTM significantly reduced albedo (0.23), causing positive iRF (warming). iRF was -3.34 ± 0.69 W m-2 and -2.78 ± 0.77 W m-2 for NT in the first and second cropping year, respectively, and increased from 1.14 ± 0.21 W -2 (2021/22) to 2.77 ± 0.41 W m-2 (2022/ 23) under NTM. Overall, our results suggest that the soil background albedo is an important site characteristic that needs to be considered and demonstrates the importance of considering biogeophysical effects when promoting practices of CA for climate change mitigation
Quantum cosmological background superposition and perturbation predictions
No full textInternational audiencePredictions from early universe cosmology typically concern primordial perturbations generated during epochs where effects arising from the quantum nature of gravity may be important; quantum vacuum fluctuations being stretched to cosmological scales during a phase of inflation. Quantizing the background is then done by assuming a single close-to-classical state over which perturbations grow, as well as a Born-Oppenheimer factorization throughout the relevant phase. We present a scenario in which although the latter factorization remains valid at all times, we allow the background state to be very non-classical by defining quantum trajectories through an eikonal approximation. We find that these trajectories asymptotically reproduce an almost classical behavior for the background, but the predictions for the power spectrum of perturbations can significantly differ
Intraplate Volcanism Driven by Slab‐Plume Interaction: Numerical Modeling and Its Application to the Eifel, Massif Central and Hainan Volcanic Areas
No full textInternational audienceIntraplate volcanism has long been linked to deep mantle plumes. However, recent studies showed that intraplate magmatism can originate from transition zone dynamics, where lower‐mantle plumes might be ponding, creating a Thermal Boundary Layer (TBL). Inspired by intraplate volcanoes in Eifel, Massif Central and Hainan that are distributed near tips of stagnant slabs imaged at transition zone depth, we hypothesize that subducted slabs might destabilize the TBL and trigger upper mantle plumes (secondary plumes), leading to intraplate volcanism. So far, the generation of such secondary plumes and the influence of slabs on plumes remain poorly understood. In this study, we perform 2D upper‐mantle geodynamic models with a TBL imposed at 670 km depth interacting with a slab of an intra‐oceanic subduction zone. The effects of various slab geometries (rollback, rollover and intermediate), TBL temperature and heating time are tested. Our models show that slabs of all geometries can destabilize the TBL, initiating secondary plumes ahead of and behind the slab. All plumes are deflected by the slab‐induced mantle flow and a sinking slab may even suppress plumes beneath it. However, a higher TBL temperature and a longer pre‐subduction heating duration may increase buoyancy flux of secondary plumes, making them more resistant to slab‐driven flow. Under all conditions explored in this study, the strength of secondary plumes produced in our models is comparable to that of the Eifel plume. This paper elucidates slab‐plume interaction and their impact on intraplate volcanism with applications to the Eifel, Massif Central and Hainan volcanic areas