The icy moons of Jupiter

Jupiter is a giant ball of gas which is 10 times larger than the planet we live on. Naturally, the magnetic field it produces is also stronger, more than 20 times Earth's magnetic field!

While we need to understand Earth's field for our day to day tasks like navigation, we study Jupiter's field to understand the evolution of the Solar System. One major consequence of the strong field of Jupiter is its effect on the Galilean moons.

The Galilean moons, namely Io, Europa, Ganymede and Callisto are the biggest four moons that orbit Jupiter. Making use of the limited data we have from them, we believe that the moons have a conducting liquid near the surface. This liquid is most likely an ocean of water and salts except in Io where we think its a magma ocean. The evidence for this primarily comes from magnetic field measurements of the moons. 

Magnetic field provides a unique way to study the interior of the object that produces it. Thanks to it and the satellites that take the instrument to measure it, we can study the electromagnetic induction in the moons of Jupiter sitting in our offices on Earth. When there is a periodically varying field near a body which has conducting material, induction takes places inside the body which produces a magnetic field. In this case, the time varying field is the large magnetic field of Jupiter and the conducting material is the subsurface ocean of the moons. If we study the induced field from the satellite measurements, we can find properties like the depth, conductivity and thickness of these oceans. All we need are magnetic observations from near the moons. While it seems easy, we do have to wait a few years before ESA's JUpiter ICy Moons Explorer (JUICE) and NASA's Europa Clipper missions can reach and transmit their observations from the Jovian system!

Image credits: ESA

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Shivangi Sharan is a postdoctoral research associate at Imperial College London, working on prioritising the research that will be carried out using the JUICE magnetometer data. Previously, she has worked on the interior of Mars and Jupiter using their magnetic observations. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

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