Magnetic Field

Image credit: JPL/NASA

This task can be made easier by varying the flyby paths in such a way that the external field can be determined, and then pulled from the internal. The image to the right, which actually shows potential flyby paths for the Clipper mission, visualizes this idea.

In the galileo missions, several important traits of the magnetic field around Europa were found. First, there is a dominant southward-orientated magnetic field from Jupiter's magnetosphere, which is about constant (~450 nT). It was also found that the Jupiter magnetospheric field's effect on Europa's equatorial plane varies with Jupiter's rotational period (called the synodic period).  This variance, with an amplitude of ~250 nT, occurs because Jupiter's magnetic dipole axis is not the same as the rotational axis, just as Earth's is not (hence true north versus magnetic north). The final major trait seen was another much smaller variance, caused by the orbital period of Europa (~14 nT amplitude) over a far larger period.

Image credit: JPL/NASA

These results confirm that Europa does have an induced dipole, strongly suggesting the existence of a liquid ocean. But the results were not entirely conclusive, as there are alternatives to the liquid ocean hypothesis, such as a layer of warm convecting layer of ice, as seen in image to the left. in order to define for certain what Europa is made of, more data than what Galileo collected is required. However, the upcoming Clipper mission shows potential to finally unravel the mysteries of Europa. In fact, several NASA scientists are confident that they can discern Europa's innards to the point of actually mapping out its subsurface ocean based on only the magnetic field. There are several skeptics that doubt the magnetic field will reveal Europa to such extent, but few doubt that the data will at least reveal the composition of Europa.

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