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This image shows the magnetic field lines of a planet passing by a moon and creating a wake.
Click on image for full size
J. Linker

Wake

A moon which is inside a magnetosphere usually travels slower than the magnetic field. This means that the magnetic field lines will pass over the satellite like water going around a rock. Because the moon is made of conducting material, the magnetic field will be delayed in passing around the moon. Thus the field lines will be distorted in passing over the satellite. Eventually they straighten up. The region upstream of the satellite, in the magnetic field of the planet, is called a satellite wake.

This satellite wake is different from the satellite geometric wake. The satellite wake extends in front of the satellite, in the direction in which it is moving, while the geometric wake extends in the opposite direction from the line between the satellite and the planet, and is similar to the shadow of the satellite.

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