Unlike ozone production in Earth's atmosphere, Ganymede's ozone is produced by charged particles trapped in Jupiter's powerful magnetic field (much like the Earth's Van Allen radiation belts). Jupiter's 9-hour, 59-minute rotation sweeps these particles along at tremendous speed, where they overtake the slower moving Ganymede and rain down onto the surface. The charged particles penetrate the ice surface where they disrupt water molecules, but the exact steps leading to ozone production are not yet fully understood, according to Noll.
Though no atmosphere has yet been detected on Ganymede, "the evidence for all this oxygen chemistry going on in the surface ice is a strong hint that Ganymede also will turn out to have a tenuous oxygen atmosphere," said Noll. Earlier this year, Hubble detected a thin oxygen atmosphere on the Jovian moon Europa.
Ganymede, Jupiter's largest moon (5,262 kilometers or 3,280 miles in diameter; 1.5 times the size of the Earth's Moon), is thought to be composed of rock and ice beneath which lies a water/ice mantle and rocky core.
The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) for NASA, under contract with the Goddard Space Flight Center, Greenbelt, Maryland. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).
CONTACT: Ray Villard FOR RELEASE: October 10, 1995 Space Telescope Science Institute (Phone: 410-338-4514) Keith Noll Space Telescope Science Institute, Baltimore, MD (Phone: 410-338-1828) PRESS RELEASE NO.: STScI-PR95-36