Creationist scientist Dr Russell Humphreys shows a young-age creation perspective has real explanatory power for understanding magnetic fields of planets, moons, and other objects in space. The Ganymede moon of Jupiter has been shown to have its own magnetic field which should not be the case if the Cosmos is billions of years old. Humphreys became famous because he successfully predicted the magnetic field of Uranus before Voyager 2 flew by the Uranus system in 1986. The strength of the magnetic field was a complete surprise to evolutionists, though not to creationists, as creationist physicist Dr. Russell Humphreys, using Biblical assumptions, had accurately predicted the strength two years previously!

This is a complex article but at least make sure you read the Conclusion.

Ganymede is the largest moon (Jupiter) in the solar system (figure 1). With a radius of 2,634 km, Ganymede is slightly larger than the planet Mercury. A unique feature of Ganymede is that it possesses its own intrinsic magnetic field. To planetary scientists, it has been a challenge to explain how an object of Ganymede’s size could still possess its own magnetic field after over 4 Ga. After billions of years, an object of Ganymede’s size would be expected to have cooled down so that there would not be adequate heat to drive a magnetic dynamo. A dynamo requires a molten iron core that can have a convection motion of the fluid, which carries an electric current. But for Ganymede, the iron core is only approximately 700–800 km in radius. Ganymede may not have a solid iron core but has a liquid iron core surrounded by a silicate mantle, and then layers of water ice over the mantle.

Ganymede is influenced by the strong magnetic field of Jupiter, but there is a good consensus among scientists that it possesses its own intrinsic field. The Galileo spacecraft conducted magnetometer measurements which have been analyzed in relation to Jupiter’s field. Ganymede’s main dipole field was measured as 719 nanotesla (nT) and is tilted 176° in relation to its own spin axis. This makes it roughly antiparallel to Jupiter’s magnetic field.

The magnetic field model of Dr. D. Russel Humphreys has been more successful than old-age magnetic dynamo theories. Humphreys applied his model to the magnetic fields of Earth, Uranus, Neptune, Mercury, our Sun, and bodies in our solar system. Mercury is slightly smaller than Ganymede but possesses a larger iron core with both solid and liquid layers. Humphreys’ model proposed that when God created the planets he initially made them out of water in the manner described for Earth in Genesis 1 and 2 Peter 3, “out of water”.

This model has significant advantages over the old-age dynamo model. The dynamo model requires a molten conducting core such as liquid iron. It also requires convection motion of the fluid and is very dependent on the size of the core and the rate of rotation of the planet. But in Humphreys’ model, the core need not actually be melted, it just needs to be a conductor. The initial magnetic field from creation decays to the present. This has been described as ‘free decay’ because the field decreases in intensity over thousands of years. Humphreys’ model assumes a young age for the Earth and solar system and leads to realistic values for the magnetic dipole moment for Earth, Mercury, and the other planets. This makes Humphreys’ model more broadly applicable than dynamo theories. Thus, it can be applied to Ganymede as well, as Humphreys has done.

In Humphreys’ model for the creation of magnetic fields, the exact composition of the iron core after creation is not known, but this does not create a problem in applying the model. The core’s composition is estimated by interior structure models that attempt to match the overall density of the moon to gravity measurements taken by spacecraft (the Galileo mission). Today, Ganymede is believed to have an ice shell of roughly 200 km, then a silicate mantle of about 1,700 km, and this leaves the core as roughly 700–800 km in radius. However, these are only rough approximations. If the core is smaller, it needs to have a composition closer to pure iron in order to generate the measured magnetic field. But if the core is larger, then it could have a composition more in a light element such as sulfur (in FeS). In Sohl 2002, an analysis was done of the Galileo gravity data for the Galilean moons of Jupiter. They describe Ganymede’s magnetic field thus:

“Magnetometer measurements of the Galileo spacecraft have shown that Ganymede possesses an intrinsic magnetic field with equatorial and polar field strengths at the surface of 750 and 1,200 nT, respectively.”

They go on to give a range of values on the size of the Ganymede core: “The ice shell was suggested to be about 800 km thick. The core may have a radius between 400 and 1,300 km.” All these values are consistent with Humphreys’ model.


At creation, should we assume that the composition of the core was uniform throughout? This is a simplifying assumption but not really a requirement. If there was a composition gradient in the core initially where it was closer to pure iron at the core-mantle boundary but possessed more FeS at the bottom of the core, this would be unstable and so sinking iron ‘snow’ and rising FeS would be possible. Such a composition gradient could alter how rapidly the magnetic field decays for some period of time until the core reached a more stable uniform composition. So, to this author, it seems the ‘iron snow’ concept is possible, but it would not drive a dynamo in Ganymede, and it would not invalidate Humphreys’ magnetic model. Thus, a young-age creation perspective has real explanatory power for understanding magnetic fields of planets, moons, and other objects in space.

This article by Wayne Spencer The iron snow dynamo theory for Ganymede is taken from The Journal of Creation 2022 Volume 36, Issue 3 in the section Perspectives.

The Journal of Creation is the Technical Journal produced by Creation Ministries International (CMI). They also produce the excellent Creation Journal for nontechnical people. Go to to subscribe.

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