Ganymede Has a Magnetic Field

Investigators recently discovered that Ganymede, in orbit around Jupiter, is the only moon in our entire solar system to feature a magnetic field. Thus far, studies only identified such structures on planets such as Earth and some of the gas giants.

One of the easiest way to check for the existence of magnetic fields is to try and see whether the object you are interested in features auroras at its poles. The northern/southern lights are always produced by the interactions between a magnetosphere and charged particles from the Sun.

The latter come in waves, and slam against specific layers of the atmosphere, that repel the. However, there is currently no known mechanism through which a magnetosphere can exist without a magnetic field. And the existence of a magnetic field calls for some very specific properties.

For example, as far as our planet goes, the magnetosphere is created by the motions of the solid core inside a thick layer of magma in the mantle. The core is made up almost entirely out of iron, and so the motion creates a huge dynamo effect.

On Jupiter, a similar phenomenon is thought to be driving the massive light displays spacecraft and telescopes noticed at both poles. The auroras there are significantly brighter and more intense than they are here on Earth, Daily Galaxy reports.

Interestingly, the magnetosphere around Jupiter is augmented by the one around Ganymede, but weakened by electrically-charged particles spewed out by other moons such as Io. The latter is very active, containing the largest number of active volcanoes in the solar system.

Eruptions are known to generate large amounts of charged particles. Io is capable of sending massive plumes of such particles towards Jupiter, making them collide with the gas giant' magnetosphere, and contributing to the brightness of its auroras.

Detecting the exact mechanisms that cause auroras on Saturn and Jupiter is an especially complex task, given the complexity of the two planetary systems. Both gas giants have a lot of moons in orbit, as well as rings and intricate atmospheres.

While the NASA Cassini orbiter has been surveying Saturn since July 1, 2004, Jupiter has not been studied thoroughly in many years. The American space agency is currently getting ready to launch the Juno spacecraft, that will have this very mission.