Exoplanets, -moons, -comets

ORCHARD: A General Planetary Evolution Code

By Keith Cowing
Status Report
astro-ph.EP
April 30, 2026
Filed under , , , , , , , , , ,
ORCHARD: A General Planetary Evolution Code
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, respectively. The faint dotted line is the iron melt curve of F. Gonz´alez-Cataldo & B. Militzer (2023), and the faint dashed curve is the Mg2SiO4 melt curve of D. C. Presnall & M. J. Walter (1993). The mantles begin fully liquid and solidify within the first 1 Myr in the bare model, but the mantles of the thin atmosphere model begin solidifying at 3-4 Gyrs. The pure iron core follows the melt curve as it releases latent heat and begins to solidify. The inner core regions solidify first, and the outer core regions cool faster as they begin to solidify. After the core fully solidifies, heat transport is solely by conduction, creating extended temperature gradients between the mantle and the inner, partially molten core. Inserting an envelope into the model, even if it comprises only 0.01% of its mass, affects its thermal evolution by inhibiting cooling. — astro-ph.EP

We present ORCHARD, a publicly available planetary evolution code based on the gas giant evolution code, 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⊕ to 10 MJ.

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.

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 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.

Roberto Tejada Arevalo, Adam Burrows, Ankan Sur, Yubo Su

Comments: 34 pages, 11 Figures, 4 Tables, 2 Appendices. Submitted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2604.24845 [astro-ph.EP] (or arXiv:2604.24845v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2604.24845
Focus to learn more
Submission history
From: Roberto Tejada Arevalo
[v1] Mon, 27 Apr 2026 18:00:01 UTC (8,273 KB)
https://arxiv.org/abs/2604.24845

Astrobiology, Stellar Cartography, exoplanet,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

Follow on Twitter
MORE FROM Exoplanets, -moons, -comets