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arxiv: 2604.24845 · v1 · submitted 2026-04-27 · 🌌 astro-ph.EP · astro-ph.IM

ORCHARD: A General Planetary Evolution Code

Roberto Tejada Arevalo , Adam Burrows , Ankan Sur , Yubo Su This is my paper

Pith reviewed 2026-05-07 17:49 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.IM
keywords planetary evolution codeexoplanet modelingequation of stategas giant evolutionsuper-Earthsub-Neptuneterrestrial planetsatmospheric boundary conditions
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The pith

ORCHARD is a new code that models the structure and time evolution of planets from 0.5 Earth masses to 10 Jupiter masses using a single framework.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper introduces ORCHARD as a publicly available tool built on an existing gas giant code to simulate how planets of widely different sizes change over time and develop their internal structures. It handles both the fluid, non-adiabatic evolution of larger planets and the solidification of mantles and cores in smaller ones. A sympathetic reader would care because a unified code removes the need to switch between separate models when studying the full range of observed exoplanets and allows direct comparisons across mass regimes.

Core claim

ORCHARD is a publicly available planetary evolution code based on the gas giant evolution code APPLE. It is capable of modeling the evolution and structures of terrestrial, super-Earth, sub-Neptune, Neptune, and gas giant planets and exoplanets from 0.5 Earth masses to 10 Jupiter masses. The code supports inhomogeneous and non-adiabatic evolution of gas giants and sub-Neptunes as well as solidification of the mantles and cores of terrestrial planets, sub-Neptunes, and super-Earths. It incorporates a state-of-the-art hydrogen-helium equation of state, metal equations of state for water, ice mixtures, enstatite, olivine, and iron, and atmospheric boundary conditions ranging from non-gray radi-

What carries the argument

The ORCHARD code, which integrates hydrogen-helium and metal equations of state with flexible atmospheric boundary conditions to compute planetary evolution and internal structures across the full mass continuum.

If this is right

  • Enables consistent simulation of non-adiabatic and inhomogeneous processes inside gas giants and sub-Neptunes.
  • Models the solidification of mantles and cores in terrestrial planets, super-Earths, and sub-Neptunes.
  • Provides one public tool that covers the entire mass range from rocky bodies to gas giants without separate codes.
  • Allows use of detailed radiative-transfer atmospheres for giants and irradiated boundary conditions for smaller planets.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The code could be used to generate grids of models for direct comparison with radius and mass measurements from transit and radial-velocity surveys.
  • It might help test how internal heat transport or atmospheric escape alters the long-term evolution of sub-Neptunes.
  • Future additions of new compositions or magnetic effects could be tested against the same benchmark planets to isolate their impact.

Load-bearing premise

The incorporated hydrogen-helium and metal equations of state together with the atmospheric boundary conditions are assumed to be accurate and correctly implemented without introducing numerical or physical errors when combined in one framework.

What would settle it

Running ORCHARD on the known masses, radii, ages, and compositions of Solar System planets such as Earth, Neptune, and Jupiter and checking whether the output radii, luminosities, and internal structures match the observed values within measurement uncertainties.

Figures

Figures reproduced from arXiv: 2604.24845 by Adam Burrows, Ankan Sur, Roberto Tejada Arevalo, Yubo Su.

Figure 2
Figure 2. Figure 2: Demonstration of CD21 EOS derivatives used in ORCHARD at Y /(X +Y ) = 0.275. The top panel shows the en￾tropy-composition derivatives used within the Schwarzschild and Ledoux convective condition (Equation 16). The bot￾tom row shows the isobaric and iso-volumetric specific heats in solid and dashed lines, where the former is used in convec￾tive flux calculations (Equation 15). Notably, Equation 16 can be s… view at source ↗
Figure 3
Figure 3. Figure 3: Isentropes (constant entropy) along the range of temperatures and pressures of interest of the pure wa￾ter, AQUA (J. Haldemann et al. 2020) revised EOS of M. Cano Amoros et al. (2026) (top panel), the Mg2SiO4 ANEOS (S. L. Thompson 1990) EOS of S. Stewart et al. (2020) (mid￾dle panel), and the iron ab initio EOS of F. Gonz´alez-Cataldo & B. Militzer (2023) (bottom panel). The water EOS can be used in the en… view at source ↗
Figure 4
Figure 4. Figure 4: Luminosity evolution across the ORCHARD planetary modeling capability. In this figure, the gas giants follow the total metal content predicted by the mass-metallicity relation of Y. Chachan et al. (2025), and their atmospheres are calculated using our updated atmosphere models (Chen et al. 2026, submitted to ApJ ; C26). The Neptunian planet (17 M⊕ ) is a homogeneous model at 175 times the solar metallicity… view at source ↗
Figure 5
Figure 5. Figure 5: Atmospheric spectra evolution of the flux density as a function of wavelength of the 8 MJ model shown in Fig￾ure 4 with ORCHARD. The spectra are calculated as post-pro￾cesses using the methods described in Chen et al. (2026; submitted to ApJ ; C26). As such, ORCHARD is equipped to model atmospheric spectra for direct-imaging investigations of exoplanets. fraction; thicker lines indicate solidified regions.… view at source ↗
Figure 6
Figure 6. Figure 6: Demonstration of Solar-System gas-giant planet evolution, along with a bare (no atmosphere) 1 M⊕ mass model (in black). The initial conditions for all models are shown in thin dashed lines of the corresponding color. The top panel shows examples of traditional homogeneous evolu￾tion models for Jupiter, Saturn, Uranus, and Neptune at 3, 5, 100, and 175 times solar metallicity, respectively. The bot￾tom pane… view at source ↗
Figure 7
Figure 7. Figure 7: Demonstration of initially homogeneous Jupiter and Saturn models undergoing various degrees of helium rain with respect to the helium rain mixing length parameter, αrain, compared at 4.56 Gyr. The top row shows the helium, temperature, and atmospheric helium fraction vs. time for the Jupiter model, and the bottom row does the same for Saturn. The Jupiter and Saturn models have 3 and 5 times solar metallici… view at source ↗
Figure 8
Figure 8. Figure 8: Luminosity evolution of the initially homogeneous Saturn models shown in the bottom row of view at source ↗
Figure 9
Figure 9. Figure 9: Evolution demonstrations of 1, 3, and 10 M⊕ rocky planets with no atmosphere (bare atmospheres), shown in the left two panels as a function of pressure and radial coordinate. The line thickness represents solidification (Equation 22); thicker lines represent solid regions and thin lines liquid regions. The initial temperature profiles are plotted in thin dashed lines of the same color. As expected, smaller… view at source ↗
Figure 10
Figure 10. Figure 10: Comparison of the thermal evolution history as a function of mass coordinate of a 3 (top) and 10 M⊕ (bot￾tom) model. Both harbor a thin, 0.01% H-He by mass enve￾lope or atmosphere. As with view at source ↗
Figure 11
Figure 11. Figure 11: Thermal evolution of a 1 M⊕ model with no atmosphere (top row) and a model with a thin 0.01% H-He by mass atmosphere/envelope. Thicker line segments indicate solidified regions, with thickness varying according to the model’s melt fraction, while thin line segments indicate liquid states. The left, center, and right panels show the temperature evolution as a function of mass, radius, and pressure, respect… view at source ↗
Figure 12
Figure 12. Figure 12: Flowchart of the orchard evolution code, adapted and updated from Paper I. Blue boxes show the initialization phase; orange boxes denote the main computational steps within each timestep; yellow diamonds are decision points for step acceptance and loop termination; the violet box marks data output, and green dashed boxes indicate auxiliary modules called by the core routines. If the combined validity and … view at source ↗
read the original abstract

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. 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.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript presents ORCHARD, a publicly available planetary evolution code extending the APPLE gas-giant framework. It claims to model the evolution and internal structures of planets across 0.5 M_⊕ to 10 M_J, including terrestrial planets, super-Earths, sub-Neptunes, Neptunes, and gas giants. Key features include support for inhomogeneous/non-adiabatic evolution, mantle/core solidification, state-of-the-art H-He and metal EOS (water, enstatite, olivine, iron), and switchable atmospheric boundary conditions from non-gray radiative transfer to irradiated and bare-rock cases.

Significance. If the implementation proves robust, ORCHARD would offer a useful unified platform for the community, allowing consistent modeling across the planetary mass continuum without switching codes. The modular design, public release, and incorporation of published EOS tables are clear strengths that could enable reproducible studies of exoplanet populations and Solar-System analogs.

major comments (1)
  1. The manuscript describes the modular architecture and EOS integration but provides no quantitative validation tests, benchmark comparisons (e.g., against known pure H-He or pure-rock limits), or error/convergence analysis for the new solidification and metal-EOS modules. This is load-bearing for the central claim that the code reliably spans the full 0.5 M_⊕–10 M_J range without introducing numerical or physical artifacts at regime boundaries.
minor comments (1)
  1. The abstract and introduction repeatedly use the phrase 'state-of-the-art' for the EOS and boundary conditions without citing the specific tables or references in the main text; adding explicit citations (e.g., to the H-He EOS source) would improve traceability.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their positive assessment of ORCHARD's potential utility and for the constructive major comment. We agree that quantitative validation is essential to support the code's claimed reliability across the full mass range and will strengthen the manuscript accordingly.

read point-by-point responses

  1. Referee: The manuscript describes the modular architecture and EOS integration but provides no quantitative validation tests, benchmark comparisons (e.g., against known pure H-He or pure-rock limits), or error/convergence analysis for the new solidification and metal-EOS modules. This is load-bearing for the central claim that the code reliably spans the full 0.5 M_⊕–10 M_J range without introducing numerical or physical artifacts at regime boundaries.

    Authors: We agree that the absence of such tests in the current manuscript is a significant gap. In the revised version we will add a dedicated validation section that includes: (i) direct comparisons of pure H-He gas-giant cooling tracks and radii against the original APPLE code; (ii) structural benchmarks for pure-rock and pure-iron planets using the same published EOS tables against independent implementations; (iii) tests of the mantle/core solidification module against analytic expectations and published results for terrestrial planets; and (iv) convergence studies and error estimates for the inhomogeneous and non-adiabatic evolution modules, with explicit checks at the regime boundaries (e.g., 0.5–2 M_⊕ and 10–20 M_⊕). These additions will be accompanied by figures and tables quantifying numerical accuracy and physical consistency. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The paper presents ORCHARD as a modular software framework extending the prior APPLE gas-giant code with published EOS tables (H-He, water, enstatite, iron, etc.) and atmospheric boundary conditions drawn from external literature. No derivation, prediction, or first-principles result is claimed that reduces by construction to fitted parameters, self-citations, or ansatzes internal to this manuscript. The central claim is the existence and range of the code itself, which is self-contained as a description of implemented modules rather than a closed logical loop.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the accuracy of the incorporated EOS models and boundary conditions drawn from prior literature; no new free parameters or invented entities are introduced in the abstract.

axioms (2)
  • domain assumption The hydrogen-helium, water, rock, and iron equations of state used are accurate representations of material behavior under planetary conditions.
    Invoked when stating that ORCHARD incorporates state-of-the-art EOS for different planet types.
  • domain assumption The atmospheric boundary conditions (non-gray radiative transfer for giants, irradiated models for sub-Neptunes, bare rocky surfaces) correctly represent the outer boundary for evolution calculations.
    Stated as part of the code's capabilities for modeling evolution.

pith-pipeline@v0.9.0 · 5505 in / 1401 out tokens · 40738 ms · 2026-05-07T17:49:52.289450+00:00 · methodology

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Reference graph

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