What the extreme fields mean

Extreme worlds use an illustrative, steady surface energy balance. It estimates surface temperature and displays a prescribed pressure, or a local vapor-pressure proxy. It does not run ExoPlaSim, evolve weather, generate terrain, or calculate winds and clouds.

Cool, temperate and warm rocky worlds with nitrogen-rich air still use the original ExoPlaSim model: Earth geography, reference pressure 1.011 bar, water and trace CO₂. Its manual limits are 800–1800 W/m² sunlight, 10–2000 ppm CO₂, and 0.5–10 Earth days rotation. These are this port’s limits, not universal limits of ExoPlaSim.

Random choices and constraints

Randomize world chooses a class, then compatible gas and surface inputs, and starts its field calculation. These weights are authored exploration choices, not measured probabilities of finding planets. The same class can repeat.

Within rocky classes, sunlight favors moderate values through triangular sampling. CO₂ is sampled in log space, with bounds conditional on sunlight: 400–900 ppm below 1150 W/m²; 280–900 below 1250; 180–700 below 1420; 100–450 through 1450; and 100–300 above 1450. Rotation favors 0.8–1.6 Earth days (80%), with 1.6–3 days otherwise. These choices avoid stacking the strongest heating or cooling settings; they do not ensure an equilibrated or habitable climate.

For icy volatile worlds, nitrogen is chosen 75% of the time and methane-rich air 25%. Composition determines the sunlight and pressure ranges. The other extreme classes choose only their listed compatible gases. Albedo stays in class-specific ranges: ice 0.55–0.85; volatile ice 0.2–0.5; Venus-like 0.6–0.8; steam 0.25–0.55; and silicate 0.05–0.25.

Cold atmospheres must remain below 80% of a simple saturation-pressure estimate at the coldest grid cell. Airless ice must remain below 260 K. Venus-like estimates stay within 450–1100 K; steam needs every cell above 650 K; molten worlds need a dayside maximum of 1700–3500 K. Failed draws are resampled within their selected class, up to 64 attempts, then a checked reference is used. Manual extreme inputs are checked too.

Temperature calculation

At each cell the model balances absorbed sunlight and a small internal heat flux against a grey outgoing-radiation approximation:

T = [(absorbed sunlight + internal heat) × (1 + 0.75 τ) / σ]^(1/4)

Here σ is the Stefan–Boltzmann constant and τ is a prescribed effective infrared optical depth. Illumination combines local day/night sunlight with a daily average, blended according to the chosen solar day length. The discrete grid is normalized to a global incident average of one quarter of stellar flux. An explicitly prescribed redistribution fraction moves energy toward that global mean. Zero obliquity and a smooth sphere are assumed; orbital dynamics are not calculated.

Optical depth is zero for airless ice and rock-vapor worlds; 0.5√p for cold volatiles; 135(p/92)^0.65 for Venus-like worlds; and 3 + 0.75p^0.65 for steam, where p is pressure in bar. Redistribution is zero for airless and silicate worlds, 0.65 + 0.25p/(p+0.1) for cold volatiles, 0.96 for Venus-like worlds, and 0.90 for steam. Internal heat is 0.05 W/m², or 0.2 W/m² for silicate worlds. These coefficients are authored approximations, not tabulated gas opacities or circulation results.

The Venus reference is calibrated to a surface temperature near 735 K at 92 bar, broadly matching NASA’s description of Venus. Matching a reference does not validate other dense CO₂ climates. This model has no convection, spectral radiation, cloud feedback, ocean dynamics, or runaway-greenhouse calculation.

Pressure and phase screens

Atmospheric pressure is uniform and prescribed for ice, volatile, Venus-like and steam worlds. It is exactly zero for airless ice. The condensation screen uses a constant-latent-heat Clausius–Clapeyron approximation, p_sat = exp[B(1/T_b − 1/T)] bar, with nitrogen T_b = 77.36 K and B = 669 K, or methane T_b = 111.66 K and B = 986 K. The reference phase data come from the NIST Chemistry WebBook for nitrogen and methane. The approximation does not solve sublimation, mixtures, clouds or volatile inventories.

The 650 K steam screen is a conservative illustration rule beyond water’s critical temperature, using the IAPWS water and steam formulation as a phase reference. It is not an implementation of that formulation or a prediction of atmospheric escape.

Silicate worlds have an assumed permanent dayside. Pressure follows the local proxy min(0.1, 0.001 × exp[60000(1/2000 − 1/T)]) bar. It drops rapidly on the cold nightside. Its coefficients and cap are illustrative; no magma composition, condensation transport or mineral equilibrium is solved. Research supports the general possibility of partly molten daysides and thin rock-vapor atmospheres, but does not establish this site’s proxy.

Reading and exporting the maps

Extreme temperature and pressure have their own color scales and model label. The grid has 64 longitudes and 32 equal-area latitude bands. Pressure in the viewer is in bar; export arrays store pascals. The export includes assumptions, parameters and energy-balance diagnostics, and omits uncalculated air temperature, wind and cloud arrays. No elapsed time or ExoPlaSim provenance is attached to these estimates.

These constraints make random examples coherent within a simple model. They cannot guarantee long-term atmospheric retention, physical equilibrium in a real atmosphere, or numerical stability of long ExoPlaSim runs.