arXiv subjects

Stéphane Mazevet

Publications and source records attributed to Stéphane Mazevet.

7 recordsLinked to original sources

arXiv2026

A semi-analytical surrogate model for giant planet evolution: bypassing ordinary differential equation solvers with localised thermodynamics, softplus asymptotes, and B-spline photometry

Context. Evolutionary models translate the observable luminosity, temperature, and colours of giant planets and brown dwarfs into mass and age. Generating their cooling tracks normally requires integrating the internal energy over time with an ordinary differential equation (ODE) solver coupled to pre-computed atmospheric grids, which becomes numerically stiff at sharp transitions such as cloud condensation and the onset of electron degeneracy, and is fragile inside Bayesian retrievals. Aims. We aim to generate continuous cooling tracks and photometric light curves directly from discrete atmospheric grids, without an ODE solver. Methods. We mapped the grids into a logarithmic thermodynamic space and extracted localised surrogate models with Gaussian-weighted regressions at fixed planetary parameters. We fitted the entropy and cooling rate against the internal temperature using bounded piecewise softplus functions to capture structural and cooling-rate transitions; the radius was fitted on the same temperature axis; and band photometry was represented with fixed-knot cubic B-splines. The age followed from numerical integration of these analytic functions, and uncertainties were propagated from the residual scatter of each fit. Results. The surrogate, CoolTrack, reproduces the transition into electron degeneracy and the L-to-T spectral-type transition in the colour-magnitude diagram, converges on Solar System benchmarks, and evaluates a full evolutionary track in milliseconds on a standard desktop CPU. Conclusions. By removing the forward-modelling bottleneck, CoolTrack is suitable for direct use in Bayesian retrieval pipelines, where the age, mass, and formation entropy of a planet can be inferred jointly with its atmospheric properties.

astro-ph.EP↗

arXiv2026

Resolving core-envelope degeneracies in giant planets and sub-Neptunes: constraining the equivalence in the presence of dilute gradients

The widespread recognition of dilute, "fuzzy" cores in giant planets and massive volatile mantles in sub-Neptunes has made interior modelling a highly degenerate, multi-dimensional problem. To map these degeneracies, we present fuzzycore, an open-source static structural integrator with a unified layered architecture spanning rock-water-envelope sub-Neptunes through volatile-rich gas giants. The framework supports dense parameter sweeps over compositional gradients at fixed observed $(M_p, R_p, Z_{atm})$, enabling consistent forward-model exploration across the radius valley and the warm-giant population. It solves hydrostatic equilibrium across phase-separated iron, rock, and water layers beneath a gaseous envelope, using a highly resolved adaptive grid to model arbitrary heavy-element gradients and parameterising the dilution width to evaluate the structural impact of varying core-envelope boundaries. We benchmark fuzzycore against an evolution-derived Jupiter profile, demonstrating that when envelope boundary metallicities and integrated heavy-element budgets are matched, the macroscopic radius is robust to the exact functional topology of the gradient to within 2.3%, allowing smooth parameterisations to densely map interior degeneracies. Applying this to the sub-Neptune regime, we generate a water-world degeneracy atlas, quantifying how the required envelope metallicity and dilution width trade off against assumed water-mass fractions to reproduce a fixed planetary radius. By decoupling structural profiling from time-dependent energy transport and convective mixing, fuzzycore maps static degeneracies at resolutions that complement, rather than replace, fully evolutionary Henyey treatments, and serves as a forward-model backend for linking atmospheric metallicity priors from JWST and Ariel to deep interior architectures.

astro-ph.EP↗

arXiv2025

Bioverse: Potentially Observable Exoplanet Biosignature Patterns Under the UV Threshold Hypothesis for the Origin of Life

A wide variety of scenarios for the origin of life have been proposed, with many influencing the prevalence and distribution of biosignatures across exoplanet populations. This relationship suggests these scenarios can be tested by predicting biosignature distributions and comparing them with empirical data. Here, we demonstrate this approach by focusing on the cyanosulfidic origins-of-life scenario and investigating the hypothesis that a minimum near-ultraviolet (NUV) flux is necessary for abiogenesis. Using Bayesian modeling and the \bioverse\ survey simulator, we constrain the probability of obtaining strong evidence for or against this ``UV Threshold Hypothesis'' with future biosignature surveys. Our results indicate that a correlation between past NUV flux and current biosignature occurrence is testable for sample sizes of $\gtrsim$50 planets. The diagnostic power of such tests is critically sensitive to the intrinsic abiogenesis rate and host star properties, particularly maximum past NUV fluxes. Surveys targeting a wide range of fluxes, and planets orbiting M dwarfs enhance the chances of conclusive results, with sample sizes $\gtrsim$100 providing $\gtrsim$80\% likelihood of strong evidence if abiogenesis rates are high and the required NUV fluxes are moderate. For required fluxes exceeding a few hundred erg/s/cm$^2$, both the fraction of inhabited planets and the diagnostic power sharply decrease. Our findings demonstrate the potential of exoplanet surveys to test origins-of-life hypotheses. Beyond specific scenarios, this work underscores the broader value of realistic survey simulations for future observatories (e.g., HWO, LIFE, ELTs, Nautilus) in identifying testable science questions, optimizing mission strategies, and advancing theoretical and experimental studies of abiogenesis.

astro-ph.EP↗

arXiv2024

Interior convection regime, host star luminosity, and predicted atmospheric CO2 abundance in terrestrial exoplanets

Terrestrial planets in the Habitable Zone of Sun-like stars are priority targets for detection and observation by the next generation of space telescopes. Earth's long-term habitability may have been tied to the geological carbon cycle, a process critically facilitated by plate tectonics. In the modern Earth, plate motion corresponds to a mantle convection regime called mobile-lid. The alternate, stagnant-lid regime is found on Mars and Venus, which may have lacked strong enough weathering feedbacks to sustain surface liquid water over geological timescales if initially present. Constraining observational strategies able to infer the most common regime in terrestrial exoplanets requires quantitative predictions of the atmospheric composition of planets in either regime. We use endmember models of volcanic outgassing and crust weathering for the stagnant- and mobile-lid convection regimes, that we couple to models of atmospheric chemistry and climate, and ocean chemistry to simulate the atmospheric evolution of these worlds in the Habitable Zone. In our simulations under the two alternate regimes, we find that the fraction of planets possessing climates consistent with surface liquid water is virtually the same. Despite this unexpected similarity, we predict that a mission capable of detecting atmospheric CO2 abundance above 0.1 bar in 25 terrestrial exoplanets is extremely likely (>95% of samples) to infer the dominant interior convection regime in that sample with strong evidence (10:1 odds). This offers guidance for the specifications of the Habitable Worlds Observatory NASA concept mission and other future missions capable of probing samples of habitable exoplanets.

astro-ph.EP↗

arXiv2024

Breaking degeneracies in exoplanetary parameters through self-consistent atmosphere-interior modelling

Context: A new generation of instruments (e.g., JWST, ELTs, PLATO and Ariel) is providing atmospheric spectra and mass/radius measurements for large exoplanet populations, challenging planetary models used to interpret these findings. Aims: We develop a new model, the Heat Atmosphere Density Evolution Solver (HADES), by coupling an atmosphere and interior model self-consistently and comparing its results to observed data. Methods: Atmospheric calculations are performed under radiative-convective equilibrium, while the interior relies on recent ab initio equations of state. We ensure continuity in the thermal, gravity, and molecular mass profiles between models. Results: The model is applied to the known exoplanet database to characterize intrinsic thermal properties. We find that intrinsic temperatures (T$_{int}$) of 200-400 K, increasing with equilibrium temperature, are needed to explain radius inflation in hot Jupiters. Additionally, we perform atmosphere-interior retrievals using observed spectra and measured parameters for WASP-39 b and 51 Eridani b. For WASP-39 b, spectroscopic data breaks degeneracies in metallicity and Tint, deriving high values: Z = 14.79$^{+1.80}_{-1.91}$ x Solar and T$_{int} = 297.39^{+8.95}_{-16.9}$ K. For 51 Eridani b, we show the importance of using self-consistent models with radius as a constrained parameter, deriving a planet mass M$_{p} = 3.13^{+0.05}_{-0.04}$ M$_{J}$ and a core mass M$_{core} = 31.86^{+0.32}_{-0.18}$ M$_{E}$, suggesting formation via core accretion with a "hot start." Conclusions: Self-consistent atmosphere-interior models can efficiently break degeneracies in the structure of transiting and directly imaged exoplanets, offering new insights into exoplanet formation and evolution.

astro-ph.EP↗

arXiv2020

Coevolution of primitive methane cycling ecosystems and early Earth atmosphere and climate

The history of the Earth has been marked by major ecological transitions, driven by metabolic innovation, that radically reshaped the composition of the oceans and atmosphere. The nature and magnitude of the earliest transitions, hundreds of million years before photosynthesis evolved, remain poorly understood. Using a novel ecosystem-planetary model, we find that pre-photosynthetic methane-cycling microbial ecosystems are much less productive than previously thought. In spite of their low productivity, the evolution of methanogenic metabolisms strongly modifies the atmospheric composition, leading to a warmer but less resilient climate. As the abiotic carbon cycle responds, further metabolic evolution (anaerobic methanotrophy) may feed back to the atmosphere and destabilize the climate, triggering a transient global glaciation. Although early metabolic evolution may cause strong climatic instability, a low CO:CH4 atmospheric ratio emerges as a robust signature of simple methane-cycling ecosystems on a globally reduced planet such as the late Hadean/early Archean Earth.

q-bio.PE↗

arXiv2011

On the change in Inertial Confinement Fusion Implosions upon using an ab initio multiphase DT equation of state

Improving the description of the equation of state (EoS) of deuterium-tritium (DT) has recently been shown to change significantly the gain of an Inertial Confinement Fusion (ICF) target (Hu et al., PRL 104, 235003 (2010)). We use here an advanced multi-phase equation of state (EoS), based on ab initio calculations, to perform a full optimization of the laser pulse shape with hydrodynamic simulations starting from 19 K in DT ice. The thermonuclear gain is shown to be a robust estimate over possible uncertainties of the EoS. Two different target designs are discussed, for shock ignition and self-ignition. In the first case, the areal density and thermonuclear energy can be recovered by slightly increasing the laser energy. In the second case, a lower in-flight adiabat is needed, leading to a significant delay (3ns) in the shock timing of the implosion.

physics.plasm-ph↗