arXiv subjects

Roberto Tejada Arevalo

Publications and source records attributed to Roberto Tejada Arevalo.

14 recordsLinked to original sources

arXiv2026

An Infant Sub-Saturn in Scorpius-Centaurus

We report the discovery and validation of TIC 88297141 Ab, a transiting planet orbiting a pre-main-sequence M dwarf (0.31 solar masses, 0.74 solar radii) in the Scorpius-Centaurus OB association. Group membership implies an age of $15.6 \pm 1.6$ Myr, supported by lithium and isochrone age-dating. We detected the TESS transits using a custom pipeline designed for variable stars and used ground-based photometry (LCO/Swope and LCOGT/Sinistro) to confirm the on-target nature of the signal. Our global fit of the transits and stellar activity gives an orbital period of 4.64 days and a planet radius of $7.21 \pm 0.32$ Earth radii (0.64 Jupiter radii). The star has a comoving M-dwarf companion (0.4 solar radii) at a projected separation of $260$ au; speckle imaging (Gemini-S/Zorro) reveals no additional stellar companions, and radial velocities from Magellan/PFS are consistent with stellar activity, giving $M_p \sin i < 4.7$ Jupiter masses at $2σ$. A statistical validation analysis yields a false positive probability of $10^{-5}$, validating the planet. A mass measurement will determine whether TIC 88297141 Ab is a low-density super-puff, like other comparably sized planets at these ages, or an unusually massive planet for its radius.

astro-ph.EP↗

arXiv2026

ORCHARD: A General Planetary Evolution Code

We present \texttt{ORCHARD}, a publicly available planetary evolution code based on the gas giant evolution code, \texttt{APPLE}, capable of modeling the evolution and structures of terrestrial, super-Earth, sub-Neptune, Neptune, and gas giant planets and exoplanets from 0.5 M$_\oplus$ to 10 M$_J$. It supports not only the inhomogeneous and non-adiabatic evolution of gas giants and sub-Neptunes, but also the solidification of the mantles and cores of terrestrial planets, sub-Neptunes, and super-Earths. \texttt{ORCHARD} incorporates a state-of-the-art hydrogen-helium equation of state, ``metal" equations of state (water, ice mixtures, enstatite/perovskite, olivine/forsterite, iron), and atmospheric boundary conditions ranging from detailed non-gray radiative transfer models for Solar System giants to irradiated sub-Neptune atmospheres and bare rocky surfaces. \txt{ORCHARD} also supports static calculations with state-of-the-art equations of state. The purpose of \texttt{ORCHARD} is to provide the scientific community with a flexible, unified tool for modeling planetary structures and evolution across the entire mass continuum of general astrophysical and planetary interest.

astro-ph.EP↗

arXiv2026

Next-Generation Atmosphere Models for Giant Planets with Application to Coupled Interior Composition and Spectral Evolution I: Cloudless Models with Equilibrium Chemistry

We present updated atmosphere models designed for calculating the post-formation evolution and cooling of giant planets with masses between $0.3$ and $10$ $M_J$. Our tables provide the entropy in the convective region at the base of the atmosphere, temperature ($T$)pressure ($P$) profiles, and emergent spectra for atmospheres calculated using the radiative transfer code \texttt{CoolTLusty} for $T_{\mathrm{eff}}$s over the range 100 to 1400 Kelvin and log$_{10}$($g$) from 2.8 to 4.4 ($cgs$) with the latest opacities and equations of state. Each spectrum and thermal profile is calculated using line-by-line opacity sampling. We construct tables at 3 different metallicities ($Z = 1, 3.16, 10 Z_\odot$) and 2 different helium fractions ($Y=0.15, 0.275$), with the improvement that we adopt a metal-inclusive EOS that treats heavy elements consistently with the opacity metallicity (rather than folding it into an effective $Y$). The result is tables that accommodate both changes in $Y$ due to helium rain and potential variations in $Z$ during envelope evolution. We present a comparison between TP profiles, modeled spectra, and evolutionary tracks, and find that on-the-fly interpolation of boundary conditions in atmospheric composition has a notable impact on the late stages of giant planet evolution, altering the timing of helium rain and therefore the subsequent cooling history and atmospheric helium depletion. We also provide an available toolkit that generates spectra and boundary conditions via efficient interpolation across the 4D parameter space $(T_{\rm eff}, \log_{10} g, Y, Z)$, which is useful for post processing evolutionary tracks to produce fully time-resolved spectral evolutions.

astro-ph.EP↗

arXiv2026

Sub-Neptune Memories I: Implications of Inefficient Mantle Cooling and Silicate Rain

We explore the evolution of sub-Neptune (radii between $\sim$1.5 and 4 R$_\oplus$) exoplanet interior structures using our upgraded evolution code, \texttt{APPLE}, which self-consistently couples the thermal and compositional evolution of the whole structure. We incorporate stably stratified regions with convective mixing and, for the first time, ab initio results on the phase separation of silicate-hydrogen mixtures to model silicate rain in sub-Neptune envelopes. We demonstrate that inefficient mantle cooling can retain sufficient heat to Gyr ages: inefficient heat transport from mantle to envelope alone keeps radii $\sim$10\% larger than predicted by adiabatic models at late times. Silicate rain can contribute an additional $\sim$5\% to the radius, depending on envelope mass and initial metal abundance. The silicate-hydrogen immiscibility region may lie in the middle or even upper envelope, far above the envelope-mantle boundary layer, and bifurcates the envelope into two an upper, hydrogen-rich region and a lower, metal-rich region above the mantle. If silicate rain occurs, atmospheres should appear depleted of silicates while radii remain inflated at late ages. To demonstrate the effects of inefficient mantle cooling, we present interior evolution models for GJ 1214 b, K2-18 b, TOI-270 d, and TOI-1801 b, showing that hot, liquid silicate mantles with thin envelopes reproduce their radii and mean densities, providing an alternative to water-world interpretations. These results imply that bulk compositions inferred from mean density must account for the mantle thermal state and the envelope mixing/phase-separation history; such thermal ``memories'' may constrain formation entropies and temperatures when metallicities are more precisely measured.

astro-ph.EP↗

arXiv2026

Saturn's Evolutionary History and Seismology: Survival of Deep Stably Stratified Regions in Evolutionary Models of Saturn Consistent with Ring Seismology

With recent advances in the modeling of the solar system giant planets, rapid progress has been made in understanding the remaining questions pertaining to their formation and evolution. However, this progress has largely neglected the significant constraints on the interior of Saturn's structure imposed by the observed oscillation frequencies in its rings. Here, we study initial conditions for Saturn's evolution that, after $4.56\;\mathrm{Gyr}$ of evolution, give rise to planetary structures admitting oscillation frequencies consistent with those observed via Saturn's ring seismology. Restricting our attention to models without compact rocky cores, we achieve simultaneous good agreement with most observed properties of Saturn at the level of current evolutionary models and with key frequencies in the observed oscillation spectrum. Our preliminary work suggests that Saturn's interior stably stratified region may be moderately less extended ($\sim 0.4$--$0.5R_{\rm Sat}$) than previously thought, which is important for reconciling the seismic constraints with evolutionary models. We also tentatively find that the deep helium gradients inferred by previous, static structural modelling of Saturn's ring seismology may not be required to reproduce the observed seismology data.

astro-ph.EP↗

arXiv2026

Next-Generation Improvements in Giant Exoplanet Evolutionary and Structural Models

Many evolutionary models of giant exoplanets still rely on simplifying assumptions that are no longer adequate given detailed constraints from Jupiter, Saturn, and modern exoplanet observations. Here, we identify the key physical improvements required for next-generation planetary evolution models using our code, \texttt{APPLE}, which enables systematic emulation and extension of legacy studies. We quantify the effects of updated equations of state, helium rain, fuzzy cores, non-adiabatic and compositionally inhomogeneous envelopes, and improved atmospheric boundary conditions by first isolating the impact of each physical ingredient and then constructing combined baseline models for planets with masses between 0.3 and 4~$M_{\rm Jup}$ to assess their collective influence on planetary structure and observable properties. We find that the adoption of modern equations of state and realistic heavy-element distributions leads to systematic, but sometimes subtle, differences ($\sim 5$ to 10\%) in radius evolution, while helium rain and the treatment of convection can significantly alter thermal histories and atmospheric compositions (by $\sim$ 5 to 20\%). These updated physical processes must be incorporated into the next-generation exoplanet evolutionary models to achieve physically consistent interpretations of planetary observations.

astro-ph.EP↗

arXiv2025

The Evolution of Jupiter and Saturn as a function of the Parameter R$_ρ$

Computed using the APPLE planetary evolution code, we present updated evolutionary models for Jupiter and Saturn that incorporate helium rain, non-adiabatic thermal structures, and "fuzzy" extended heavy-element cores. Building on our previous Ledoux-stable models, we implement improved atmospheric boundary conditions that account for composition-dependent effective temperatures and systematically explore the impact of varying the parameter $R_ρ$, which allows one to explore in an approximate way the efficiency of semiconvection. For both Jupiter and Saturn, we construct models spanning from $R_ρ=1$ (Ledoux) to $R_ρ=0$ (Schwarzschild), and identify best-fit solutions that match each planet's effective temperature, equatorial radius, lower-order gravitational moments, and atmospheric composition at 4.56 Gyr. We find that lower $R_ρ$ values lead to stronger convective mixing, resulting in higher surface metallicities and lower deep interior temperatures, while requiring reduced heavy-element masses and lower initial entropies to stabilize the dilute inner cores. Our Saturn models also broadly agree with the observed brunt frequency profile inferred from Cassini ring seismology, with stable layers arising from both the helium rain region and the dilute core. These findings support the presence of complex, compositionally stratified interiors in both gas giants.

astro-ph.EP↗

arXiv2025

Different Inhomogeneous Evolutionary Histories for Uranus and Neptune

We present updated non-adiabatic and inhomogeneous evolution models for Uranus and Neptune, employing an interior composition of methane, ammonia, water, and rocks. Following formation trends of the gas giants, Uranus and Neptune formation models are applied, where both planets begin with layers stable to convection. Both planets are subject to convective mixing throughout their evolution. Consistent with past work on this subject, the interior heat of Uranus evolution models is preserved by the stability of an outer composition gradient at lower initial entropy, where convective mixing is inhibited over evolutionary timescales. In contrast, if Neptune's initial entropy is enough to convectively mix its envelope, it undergoes homogenization and adiabatic cooling of the outer 40\% of its envelope. The subsequent release of internal energy during Neptune's evolution, driven by the convective instability of its primordial outer compositional gradient, accounts for its higher luminosity relative to Uranus. This work proposes that the observed luminosity differences between Uranus and Neptune could be explained by the convective stability of their outer envelopes. The extensive convective mixing in Neptune can lead to a higher metallicity in its outer region compared to Uranus, a feature seen in atmospheric measurements and shown in past interior models of Neptune. Due to Neptune's more pronounced cooling, our models predict favorable conditions for hydrogen-water immiscibility in its envelope.

astro-ph.EP↗

arXiv2025

Simultaneous Evolutionary Fits for Jupiter and Saturn Incorporating Fuzzy Cores

With the recent realization that there likely are stably-stratified regions in the interiors of both Jupiter and Saturn, we construct new non-adiabatic, inhomogeneous evolutionary models with the same microphysics for each that result at the present time in respectable fits for all major bulk observables for both planets. These include the effective temperature, radius, atmospheric heavy-element and helium abundances (including helium rain), and the lower-order gravity moments J2 and J4. The models preserve from birth most of an extended "fuzzy" heavy-element core. Our predicted atmospheric helium mass fraction for Saturn is ~0.2, close to some measured estimates, but in disagreement with some published predictions. To preserve a fuzzy core from birth, the interiors of both planets must start out at lower entropies than would be used for traditional "hot start" adiabatic models, though the initial exterior mantle entropies can range from hot to warm start values. We do not see a helium ocean in Saturn's interior, and both models have inner envelopes with significant Brunt-Vaisala frequencies; this region for Saturn at the current epoch is more extended and in it, the Brunt is larger. The total heavy-element mass fraction in Jupiter and in Saturn is determined to be ~14% and ~26%, respectively, though there is some play in these determinations.

astro-ph.EP↗

arXiv2024

Jupiter Evolutionary Models Incorporating Stably Stratified Regions

We address the issue of which broad set of initial conditions for the planet Jupiter best matches the current presence of a ``fuzzy core" of heavy elements, while at the same time comporting with measured parameters such as its effective temperature, atmospheric helium abundance, radius, and atmospheric metallicity. Our focus is on the class of fuzzy cores that can survive convective mixing to the present day and on the unique challenges of an inhomogeneous Jupiter with stably-stratified regions now demanded by the \textit{Juno} gravity data. Hence, using the new code \texttt{APPLE}, we attempt to put a non-adiabatic Jupiter into an evolutionary context. This requires not only a mass density model, the major relevant byproduct of the \textit{Juno} data, but a thermal model that is subject to interior heat transport, a realistic atmospheric flux boundary, a helium rain algorithm, and the latest equation of state. The result is a good fit to most major thermal, compositional, and structural constraints that still preserve a fuzzy core and that should inform future more detailed models of the current Jupiter in the context of its evolution from birth.

astro-ph.EP↗

arXiv2024

Equations of State, Thermodynamics, and Miscibility Curves for Jovian Planet and Giant Exoplanet Evolutionary Models

The equation of state of hydrogen-helium (H-He) mixtures plays a vital role in the evolution and structure of gas giant planets and exoplanets. Recent equations of state that account for hydrogen-helium interactions, coupled with hydrogen-helium immiscibility curves, can now produce more physical evolutionary models, such as accounting for helium rain with greater fidelity than in the past. In this work, we present a set of tools for planetary evolution\footnote{All tables of thermodynamic quantities and derivatives are available at \url{https://github.com/Rob685/hhe_eos_misc}, along with a unified Python interface. Tutorials demonstrating the interface are also available in the repository.} that provides a Python interface for existing tables of useful thermodynamic quantities, state-of-the-art H-He equations of state, and pressure-dependent H-He immiscibility curves. In particular, for a collection of independent variable choices, we provide scripts to calculate the variety of thermodynamic derivatives used to model convection and energy transport. These include the chemical potential derived from the internal energy, which is a modeling necessity in the presence of composition gradients when entropy is the other primary variable. Finally, an entropy-based convection formalism is presented and fully described that highlights the physical differences between adiabatic and isentropic interior models. This centralized resource is meant to facilitate both giant planet structural and evolutionary modeling and the entry of new research groups into the field of giant planet modeling.

astro-ph.EP↗

arXiv2024

APPLE: An Evolution Code for Modeling Giant Planets

We introduce APPLE, a novel planetary evolution code designed specifically for the study of giant exoplanet and Jovian planet evolution in the era of Galileo, Juno, and Cassini. With APPLE, state-of-the-art equations of state for hydrogen, helium, ice, and rock are integrated with advanced features to treat ice/rock cores and metals in the gaseous envelope; models for helium rain and hydrogen/helium immiscibility; detailed atmosphere boundary tables that also provide self-consistent albedos and spectra; and options to address envelope metal gradients and stably-stratified regions. Our hope is that these purpose-built features of APPLE will help catalyze the development of the next generation of giant exoplanet and Jovian planet evolutionary models.

astro-ph.EP↗

arXiv2023

Jupiter Atmospheric Models and Outer Boundary Conditions for Giant Planet Evolutionary Calculations

We present updated atmospheric tables suitable for calculating the post-formation evolution and cooling of Jupiter and Jupiter-like exoplanets. These tables are generated using a 1D radiative transfer modeling code that incorporates the latest opacities and realistic prescriptions for stellar irradiation and ammonia clouds. To ensure the accuracy of our model parameters, we calibrate them against the measured temperature structure and geometric albedo spectrum of Jupiter, its effective temperature, and its inferred internal temperature. As a test case, we calculate the cooling history of Jupiter using an adiabatic and homogeneous interior and compare with extant models now used to evolve Jupiter and the giant planets. We find that our model reasonably matches Jupiter after evolving a hot-start initial condition to the present age of the solar system, with a discrepancy in brightness temperature/radius within two per cent. Our algorithm allows us to customize for different cloud, irradiation, and metallicity parameters. This class of boundary conditions can be used to study the evolution of solar-system giant planets and exoplanets with more complicated interior structures and non-adiabatic, inhomogeneous internal profiles.

astro-ph.EP↗

arXiv2022

Stability Constrained Characterization of the 23 Myr-old V1298 Tau System: Do Young Planets Form in Mean Motion Resonance Chains?

A leading theoretical expectation for the final stages of planet formation is that disk migration should naturally drive orbits into chains of mean motion resonances (MMRs). In order to explain the dearth of MMR chains observed at Gyr ages ($<1\%$), this picture requires such configurations to destabilize and scramble period ratios following disk dispersal. Strikingly, the only two known stars with three or more planets younger than $\lesssim 100$ Myrs, HR 8799 and V1298 Tau, have been suggested to be in such MMR chains, given the orbits' near-integer period ratios. We incorporate recent transit and radial velocity observations of the V1298 Tau system, and investigate constraints on the system's orbital architecture imposed by requiring dynamical stability on timescales much shorter than the system's age. We show that the recent radial-velocity mass measurement of V1298 Tau $b$ places it within a factor of two of the instability limit, and that this allows us to set significantly lower limits on the eccentricity ($e_b \leq 0.17$ at $99.7\%$ confidence). Additionally, we rule out a resonant chain configuration for V1298 Tau at $\gtrsim 99\%$ confidence. Thus, if the $\sim 23$ Myr-old V1298 Tau system did form as a resonant chain, it must have undergone instability and rearrangement shortly after disk dispersal. We expect that similar stability constrained characterization of future young multi-planet systems will be valuable in informing planet formation models.

astro-ph.EP↗