December 14, 2000
Photo No: H2000-38a
Satellite Footprints Seen in Jupiter Aurora
This is a spectacular NASA Hubble Space Telescope close-up view of an
electric-blue aurora that is eerily glowing one half billion miles away
on the giant planet Jupiter. Auroras are curtains of light resulting
from high-energy electrons racing along the planet's magnetic field into
the upper atmosphere. The electrons excite atmospheric gases, causing
them to glow. The image shows the main oval of the aurora, which is
centered on the magnetic north pole, plus more diffuse emissions inside
the polar cap.
Though the aurora resembles the same phenomenon that crowns Earth's
polar regions, the Hubble image shows unique emissions from the magnetic
"footprints" of three of Jupiter's largest moons. (These points are
reached by following Jupiter's magnetic field from each satellite down
to the planet).
Auroral footprints can be seen in this image from Io (along the left
hand limb), Ganymede (near the center), and Europa (just below and to
the right of Ganymede's auroral footprint). These emissions, produced by
electric currents generated by the satellites, flow along Jupiter's
magnetic field, bouncing in and out of the upper atmosphere. They are
unlike anything seen on Earth.
This ultraviolet image of Jupiter was taken with the Hubble Space
Telescope Imaging Spectrograph (STIS) on November 26, 1998. In this
ultraviolet view, the aurora stands out clearly, but Jupiter's cloud
structure is masked by haze.
December 14, 2000 inaugurates an intensive two weeks of joint
observation of Jupiter's aurora by Hubble and the Cassini spacecraft.
Cassini will make its closest approach to Jupiter enroute to a
July 2004 rendezvous with Saturn. A second campaign in January 2001
will consist of Hubble images of Jupiter's day-side aurora and Cassini
images of Jupiterís night-side aurora, obtained just after Cassini
has flown past Jupiter. The team will develop computer models that
predict how the aurora operates, and this will yield new insights
into the effects of the solar wind on the magnetic fields of planets.
Credit: NASA/ESA, John Clarke (University of Michigan)