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Ganymede: The largest icy moon of Jupiter

Following up on our last blog about the icy moons of Jupiter, in this blog we start off with understanding the largest moon of the planet and our Solar System, Ganymede! Although we have only a few measurements from the moon through the Galileo and Juno missions orbiting Jupiter, we have quite a lot of information from them.

Ganymede is a very unique moon. It is the only moon we know of that is capable of generating its own magnetic field, possibly through a dynamo. This means that there is some conducting liquid in which convection is taking place that is producing a magnetic field of the order of ~103 nT. This dynamo is expected to be an iron and iron sulphide alloy.

While the most important and interesting insight about Ganymede is the dynamo, another fascinating feature is the presence of a subsurface ocean. However, we are still unsure if the field we observed was from an ocean or just part of the dynamo signal. When we model magnetic field data of the moon, both these possibilities arise and hence to confirm which of them are true, we would require more data from around the moon.

Once we have a wealth of measurements from future missions, we would be able to better model the magnetic field as well as other observations like the gravity field which will help us better understand its interior structure. In the meantime, drop your questions about Ganymede below and let us know what you are curious to find about the moon!


Image: Ganymede from Galileo. Credit: NASA.



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.




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




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.