What is it about Enceladus? I doubt anyone would have thought
the tiny moon would weigh so heavily in our thinking about
Saturn before Cassini, but now comes the news that Enceladus is
distorting the planet’s magnetic field to the point that it
becomes tricky to measure the length of the Saturnian day. Count
the electrically charged particles originating in the moon’s
geysers as the culprit — they’re actually causing Saturn’s
magnetic field lines to slip relative to the planet’s rotation.
The process seems to work like this: Gas particles are ejected
from the geysers on Enceladus and become electrically charged.
Captured by Saturn’s magnetic field, they form a disk of plasma
that wraps around the planet’s equator. The rotation of the
plasma disk slows down enough due to interactions with the
magnetic field that the rotation period Cassini has been
measuring — based on radio emissions — is not actually the
length of Saturn’s day. Instead, it’s the rate of rotation of
the plasma disk. Image: Geysers on Saturn’s