Ganymede’s Magnetic Mysteries

From an article in Planetaria, a fantastic blog exploring alien worlds, and my new go-to source of news!

Jupiter’s moon Ganymede is found to be producing some exceptionally strong electromagnetic waves. These waves are known as “chorus waves”, as they can be converted into sound, which we would hear as a series of bizarre chirps and whistles. In fact, they sound like an over caffeinated R2-D2!

The universe talks to us!

Ganymede is the second largest moon in the solar system after Titan, and is larger than the planet Mercury. One of the four Gallilean moons, Ganymede’s magnetic field is internally produced, unlike that of it’s sister moon Europa, whose field is induced by Jupiter’s powerful magnetic field.

This magnetism is the result of a highly differentiated internal structure. This means that like Earth, Ganymede has an active molten core, which interacts with upper layers, and also results in the presence of a subsurface ocean. Earth’s magnetic field is the result of it’s molten core and convection of molten iron and rock through the lower and upper mantle. Ganymede has a similar field but it weighs in at a million times stronger than our own! It’s even more intense than the magnetic field pumped out by its parent Jupiter!

This field results in the generation of powerful auroras, which are a familiar phenomenon on earth.

Ganymede’s complex structure is thought to be the result of a fairly quick formation period. During the formation of the solar system, Jupiter ( the oldest of the planets) was still an accreting cloud of gas and dust: a mini nebula much like the solar nebula forming around it. Within this Jovian nebula dozens or maybe hundreds of smaller worlds were accreting: emerging from the primordial Jovian cloud. Proto-Ganymede accreted quickly, within about 10000 years, and so it’s various layers were unable to disperse and homegenise within the moons structure. This can be inferred from the structure of other Jovian moons such as Callisto, which are shown to have an extremely homogeneous internal composition; indicating a more protracted period of accretion and formation. Most likely on the order of about 100000 years.

Jupiter displays impressive aurora as well. These are the result of interactions betweens it’s magnetic field and charged particles issuing from the highly volcanic moon Io.

Aurora and magnetic phenomena have been observed on exoplanets, in particular on mysterious objects known as brown dwarfs. These “failed stars” are quite common in the galaxy, and present a magnetic laboratory for astrobiologists and planet hunters. They are of considerable interest in this context, as they present an opportunity for researchers to examine an atmosphere that resembles that of both a star and a gas giant planet, all without the pesky glow from a nearby star!

Methods of detection and analysis of exo-magnetic fields such as these will not only aid scientists in understanding the formation of planets and stars, but also in the detection of exoplanets, and assessment of their potential habitability. Remember, life on Earth is protected by our magnetic field, so detection of such fields around exotic new worlds could be a hopeful sign.

Thanks for reading AstroBiological, giving you the universe in plain human. I hope you’ve learnt something today. I know I have, and that’s what it’s all about!
I’ll see you next time!

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