Magnetic Fields of Planetary Satellites
Of all the known planetary satellites, only one has been confirmed to have a magnetic field within it. With a radius of 2634 kilometers (3270 miles), Ganymede is the largest moon of the planet Jupiter, as well as the largest moon in our solar system; in fact, it is even larger than the planets Mercury and Pluto. Earth, Mercury, and the Gas Giants also have magnetic-field-generating cores; however, none of their moons have a have magnetospheres (Note: mercury does not have any moons).
Ganymede's magnetosphere is able to deflect the magnetic influence of Jupiter. When entering such a magnetic field, a magnetometer is able to detect an extremely large burst as was done by the Jet Propulsion Laboratory's Galileo Spacecraft between 1996 and 2003. Magnetospheres are also able to deflect solar winds (from our star) and winds traveling from stars located mostly in
[relatively]
nearby systems.
Based on the findings of Galileo (the spacecraft) and the density calculations based on its orbit, Ganymede's core is composed of metallic (iron, nickel, or an iron alloy) materials, surrounded by a water (liquid or frozen) mantle and a surface of ice and rock. It is believed that the metallic core is the direct cause of a magnetic field, which in turn results in a magnetosphere, protecting Ganymede's baron, cratered, surface from feeling the full effect of solar winds. This protection is two-fold, since the satellite revolves within Jupiter's giant magnetosphere.
Ganymede's magnetosphere is believed to operate the same way that Earth's does; a fluid mantle rotates around a metallic core. The resulting effect is much like the convection type of effect much the same as water boiling within a pot. On a scale as large as the Earth, or Ganymede, convection of the mantle on such a massive scale causes magnetic forces to flow outward, from one pole to the other. In a giant donut shaped, three-dimensional loop.
Earth's Magnetosphere protects the surface from particles that would otherwise cause any possible inhabitable life to become less as we know it. Ganymede's Magnetosphere (as well as Jupiter's magnetosphere) partly protects its surface from solar winds much the same way as Earth. Auroras have been detected from Jupiter's radiation effects. Though it would be like nothing else for a human to witness such effects, direct contact with the harsh surface of Ganymede would be short lived.
