This artist's sketch illustrates that the magnetic force on a charged ring
grain partly pushes particles out of the ring plane and that the strength
and direction of this out-of-plane force depends both on where the particle
is in the ring plane as well as on Jupiter's rotational orientation.
In these figures, Jupiter's spin axis is vertical; however, Jupiter's
dipolar magnetic field (dotted lines) is tilted about 10 degrees
from the planet's spin axis. Thus, the magnetic field is not perfectly
vertical when it passes through the ring plane in which the ring particles
are orbiting. (The magnetic field lines are represented by the yellow dotted
lines; the yellow arrows indicate the direction of the field.)
The magnetic forces (red arrows) on a ring particle are simultaneously
perpendicular to the particle's direction of motion (in the ring plane) and
to the magnetic field lines (yellow dotted lines). The magnetic force
on a negatively charged ring particle points mainly outward from the planet.
With Jupiter oriented as shown in the top panel, the magnetic forces have
a slightly downward force on particles at the right of Jupiter and
a slightly upward force on particles at the left of Jupiter.
The bottom panel shows Jupiter five hours later, after the planet
has rotated 180 degrees, half a rotation. At this point the part of the
magnetic force out of the equatorial plane reverses direction. Thus every
charged ring grain experiences an oscillating vertical force. Some of these
forces oscillate with periods that are multiples of the particles' orbital
periods. Such synchronous periods lead to especially large, resonant
(enhanced) effects.
The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission
for NASA's Office of Space Science, Washington, DC.
This image and other images and data received from Galileo are posted
on the World Wide Web, on the Galileo mission home page at URL
http://galileo.jpl.nasa.gov/.
Background information and educational context for the images can be found at:
http://www.jpl.nasa.gov/galileo/sepo.
