Planet and volatiles

The [planet] section defines the bulk planet properties, initial temperature profile, and volatile inventory. These parameters set the initial conditions for the coupled evolution.

Bulk properties

Parameter	Type	Default	Description
`mass_tot`	float	`1.0`	Total initial planet mass [M\(_\oplus\)]
`prevent_warming`	bool	`false`	Require monotonic cooling (clamp \(T_\mathrm{magma}\) to previous value if it increases)
`R_int_override`	float or none	`none`	Advanced: bypass the radius root finder and force a fixed interior radius [m]; `none` uses the root finder. Used for SPIDER/Aragog parity runs

Initial temperature profile

The temperature_mode parameter selects how the initial temperature distribution is constructed. Different modes anchor the profile at different reference points.

Parameter	Type	Default	Description
`temperature_mode`	str	`"liquidus_super"`	See modes table below
`tsurf_init`	float	`4000`	Surface temperature [K] (isothermal, linear, adiabatic modes)
`tcmb_init`	float	`6000`	Core-mantle boundary temperature [K] (adiabatic_from_cmb mode)
`tcenter_init`	float	`6000`	Center temperature [K] (linear mode only)
`delta_T_super`	float	`500`	Superliquidus offset at CMB [K] (liquidus_super mode)
`ini_entropy`	float	`3900`	Initial specific entropy [J/kg/K] (isentropic mode)
`ini_dsdr`	float	`-4.698e-6`	Initial entropy gradient [J/kg/K/m] (isentropic mode)
`f_accretion`	float	`0.04`	Accretion heat retention fraction [0, 1] (accretion mode)
`f_differentiation`	float	`0.50`	Differentiation heat retention fraction [0, 1] (accretion mode)

Temperature modes

Mode	Anchor point	Description
`isothermal`	`tsurf_init`	Uniform temperature throughout mantle
`linear`	`tsurf_init`, `tcenter_init`	Linear gradient from center to surface
`adiabatic`	`tsurf_init`	Adiabat anchored at the surface, integrated downward
`adiabatic_from_cmb`	`tcmb_init`	Adiabat anchored at the CMB at a fixed temperature, integrated upward
`liquidus_super`	`delta_T_super`	Adiabat anchored at \(T_\mathrm{liq}(P_\mathrm{cmb}) + \Delta T_\mathrm{super}\) (default), using the Fei et al. (2021)¹ MgSiO\(_3\) liquidus. Setting \(\Delta T_\mathrm{super} = 0\) places the IC exactly on the liquidus.
`accretion`	`f_accretion`, `f_differentiation`	Temperature from gravitational accretion and core-mantle differentiation energy retention (White and Li, 2025)
`isentropic`	`ini_entropy`, `ini_dsdr`	Entropy-based IC; the interior solver maps \(S \to T(P)\) via its EOS table

Redox state

Parameter	Type	Default	Description
`fO2_source`	str	`"user_constant"`	How fO\(_2\) is determined: `user_constant` (buffered to `outgas.fO2_shift_IW`), `from_O_budget` (derived from O mass balance)

When fO2_source = "user_constant", the atmospheric fO\(_2\) is buffered at the iron-wustite offset set by outgas.fO2_shift_IW. When fO2_source = "from_O_budget", the O budget from planet.elements.O_mode/O_budget is authoritative and the chemistry solver derives the fO\(_2\) that produces the supplied O inventory. A third value, from_mantle_redox, is reserved for a future release and is rejected at config-load until that work lands.

Volatile inventory

Parameter	Type	Default	Description
`volatile_mode`	str	`"elements"`	How to set the volatile inventory: `elements` (by elemental budgets) or `gas_prs` (by surface partial pressures)
`volatile_reservoir`	str	`"mantle"`	Reference mass for ppmw calculations: `mantle` or `mantle+core`

Element abundances `[planet.elements]`

Used when volatile_mode = "elements". Each element has a mode (defining the unit) and a budget (the value in that unit).

Parameter	Type	Default	Description
`O_mode`	str	`"ic_chemistry"`	`ic_chemistry` (defer to CALLIOPE equilibrium), `ppmw`, `kg`, `FeO_mantle_wt_pct`
`O_budget`	float	`0.0`	Oxygen inventory (ignored for `ic_chemistry` mode)
`H_mode`	str	`"oceans"`	`oceans` (Earth ocean equivalents), `ppmw`, `kg`
`H_budget`	float	`0.0`	Hydrogen inventory
`C_mode`	str	`"C/H"`	`C/H` (mass ratio to H), `ppmw`, `kg`
`C_budget`	float	`0.0`	Carbon inventory
`N_mode`	str	`"N/H"`	`N/H` (mass ratio to H), `ppmw`, `kg`
`N_budget`	float	`0.0`	Nitrogen inventory
`S_mode`	str	`"S/H"`	`S/H` (mass ratio to H), `ppmw`, `kg`
`S_budget`	float	`0.0`	Sulfur inventory
`use_metallicity`	bool	`false`	Scale C/N/S from solar metallicity (overrides C/N/S mode+budget)
`metallicity`	float	`1000`	Metallicity relative to solar, by mass

Note

The Python defaults for volatile budgets are zero. The values in all_options.toml (e.g., H_budget = 1.0) show recommended starting points for a typical rocky planet.

Partial pressures `[planet.gas_prs]`

Used when volatile_mode = "gas_prs". Sets the initial atmosphere directly by surface partial pressure for each gas species.

Parameter	Type	Default	Description
`H2O`	float	`0.0`	[bar]
`CO2`	float	`0.0`	[bar]
`N2`	float	`0.0`	[bar]
`S2`	float	`0.0`	[bar]
`SO2`	float	`0.0`	[bar]
`H2S`	float	`0.0`	[bar]
`NH3`	float	`0.0`	[bar]
`H2`	float	`0.0`	[bar]
`CH4`	float	`0.0`	[bar]
`CO`	float	`0.0`	[bar]

Fei, Y., Seagle, C.T., Townsend, J.P., et al., Melting and density of MgSiO3 determined by shock compression of bridgmanite to 1254 GPa, Nature Communications, 12, 876, 2021. SciX. ↩