Jupiter’s Personal Magnetism:

Last article we looked at the affect our own Moon has on ourselves and the planet. This week we are going to look at another way that a moon of the Solar System effects it primary.

Jupiter, rightly named after the king of the Roman gods, is the largest planet in the solar system with a mass 2.5 times greater than all the other planets combined. This massive planet, by itself, has more than sixty of the solar system’s moon orbiting it and four of those moons: Io, Europa, Ganymede and Callisto, would be classed as sub-planets (just like poor Pluto) if they were orbiting the Sun and are close in size to our own moon.

As the title suggests Jupiter has a powerful magnetic field surrounding it. This field extends into space beyond the orbits of Io and Europa. If this is a scenario that sounds familiar, Australian author Sean McMullen uses exactly this setting for his Moonworld series (see reference below). Sean’s stories are anthropomorphised fantasies set on a moon orbiting a gas giant. The very human-like inhabitants of his story world can perform ‘magic’ by interacting with the strange energies created by the moon’s passage through its primary's magnetic field.

However, in the Jovian system things are a bit more drastic.

Io is the most geologically active object in the solar system; kept that way by the tidal forces generated by its orbit around Jupiter. Jupiter’s gravity is such that much of the matter ejected by the volcanoes on Io (volcanic eruptions 330 kms high as shown in the animated gif below have been observed) does not settle back to the surface.

Image provided by NASA (and therefore not copyrighted). Obtained from the WikiMedia Commons

It either falls into gas giant or, if it is ionised, is dispersed into strange banana-like shape along the orbital path of Io by the Jovian magnetic field. Either way the titanic forces and electrical charges (I have sudden visions of gods and thunderbolts here) involved produce massive bursts of electromagnetic interference making normal radio useless and the conditions on the surface very inimical to life.

Despite the vast differences in size and mass Io, and to a lesser extent Europa, does have some effect on Jupiter ... well to be precise, on Jupiter’s magnetic field. Its passage through the heavens distorts the planet's magnetic field which would cause fluctuations in the magnetic field as observed on the planet's surface, such as it is.

And here’s a world building tip to take away with you: if your world has a magnetic field like Earth — and there are strong arguments as to why this should be the case on any planet where life has evolved; think protection from hard radiation — then you need to have geologically inactive moons to make the idea of anything like a compass plausible.

Well, that's enough for this week. For next week I'll see if I can find other ways in which moons, single or multiple could effect their primaries.


Sean McMullen’s website


About the moon, Io


N.B. Please note that I although I use the Wikipedia (and WikiMedia Commons) a lot for references, this is for expediency and the familiarity of my readers. Anyone interested in further studies should make use of the references where available and understand that the Wikipedia is a co-operative project contributable to by anyone and must always be looked at in that light.

Phill Berrie, September, 2008.