Data from: Powering ganymede’s dynamo with protracted core formation

Trinh, Kevin 1 ; Petricca, Flavio2 ; Hemingway, Douglas 3 ; Vance, Steven 2

Research facility: California Institute of Technology

Published Apr 23, 2026 on Dryad. https://doi.org/10.5061/dryad.1rn8pk17z

Data files

Apr 23, 2026 version files 240.45 KB

Code_and_data_files.zip

236.59 KB
README.md

3.86 KB

Abstract

Ganymede is the only known moon with an active dynamo today. Previous studies interpret Ganymede’s dynamo as arising from convection in a metal core that formed billions of years ago. However, Ganymede likely accreted too cold to form with a metal core, which confounds interpretations of Ganymede’s magnetic field as a constraint on the moon’s broader history. Here we re-evaluate the thermal evolution of Ganymede’s rock-metal interior from a cold start. Our models show that Ganymede’s observed dynamo is consistent with ongoing core formation—a process not yet observed elsewhere. If Ganymede has an Fe-FeS core with a sub-eutectic composition, then gradual mantle warming may expel dense Fe melt onto the growing protocore and stir liquid metal, sustaining a dynamo for billions of years.

Dataset DOI: 10.5061/dryad.1rn8pk17z

Description of the data and file structure

Our data is primarily code and model output of simulations for the thermal evolution of Ganymede. Some compiled data of Fe-FeS melting is also included.

Files and variables

Code_and_data_files.zip

The following tabulated (.csv) data files are listed below. The names and units of each column are listed in bold and in parentheses, respectively.

ps_spider_web.csv: results of the parameter sensitivity (Figure 4a–f).

Xm0 (wt.% Fe-FeS) - Initial mass fraction of metal in the rock-metal mixture.
Xs0 (wt.% S) - Initial mass fraction of sulfur in the Fe-FeS alloys.
Xw0 (wt.% H₂O) - Initial mass fraction of water in the hydrated rock endmember.
fK ([^40^K]%) - Fraction of ⁴⁰K leached throughout silicate dehydration.
PT (TW) - Total tidal dissipation in the silicate interior.
M_ice_frac (wt.% H₂O) Initial mass fraction of ocean-ice shell.
mc (kg) - Final mass of metal core.
rc (m) - Final radius of metal core.
Xsc (wt.% S) - Final composition of metal core.
rhoc (kg m^-3) - Final density of metal core.
Rem (unitless) - Magnetic Reynolds number.
MOI (unitless) - normalized moment of inertia.
R_tot (km) - Final total radius of the simulated Ganymede.

ps_mc_1000models_mag.csv: results of the parameter sensitivity (Figure 4g).

Xm0 (wt.% Fe-FeS) - Initial mass fraction of metal in the rock-metal mixture.
Xs0 (wt.% S) - Initial mass fraction of sulfur in the Fe-FeS alloys.
Xw0 (wt.% H₂O) - Initial mass fraction of water in the hydrated rock endmember.
fK ([^40^K]%) - Fraction of ⁴⁰K leached throughout silicate dehydration.
tidal (W) - Total tidal dissipation in the silicate interior.
Re_m (unitless) - Magnetic Reynolds number.
Bsurf (T) - Strength of dipolar magnetic field at Ganymede's surface.
rc (m) - Metal core radius.
rhoc (kg m^-3) - Metal core density.
t_age (Gyr) - Lifetime of dynamo. "null" indicates no ongoing dynamo.

Code/software

We provide a folder with various Python and Cython scripts, as well as saved model output. The files include:

EvolvingMoons1D-speed.py. This is the main script used to run thermal evolution models. The script must by compiled in C before running, since we use the Cython package.
evolvingmoons_speedup.pyx. This code houses the Cython functions that improve the speed of EvolvingMoons1D-speed.py. Any changes to this file requires a compile step before running the code.
HelperFunctions.py. This script houses the thermal evolution code that EvolvingMoons1D-speed.py calls, as well as other supporting functions.
PlottingScripts.py. This script includes a suite of plotting functions to visualize output from EvolvingMoons1D-speed.py.
Explore Metal Melting.py. Used to create Figure S6.
PlotParameterSensitivity.py. Plots the results of Figure 4.
setup.py. A short script used to compile the main scripts.
GridResolutionError.py. Used to create Figure S8.
recompile instructions.txt. Instructions on how to compile the main scripts.
makeFigureS4.py. Used to create Figure S4.
makeFigureS9.py. Used to create Figure S9.
evolvingmoons_speedup.c and evolvingmoons_speedup.cpython-39-darwin.so are files automatically created when compiling evolvingmoons_speedup.pyx with Cython. There is no need for the user to modify these files directly.

Access information

Other publicly accessible locations of the data:

https://github.com/ktrinh20/GanymedeDynamo