Ganymede isn’t just the largest moon in the solar system—it’s also the only moon with a magnetic field. Scientists think this comes from a liquid iron core, just like Earth’s. The result? Ganymede has its own tiny magnetosphere, which partially shields it from Jupiter’s brutal radiation. If you could stand on its surface (with a proper spacesuit, of course), you’d be walking on the closest thing to a “mini planet” orbiting a gas giant.
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