![]() "These beams are a signature of remarkable particle acceleration processes that occur in the vicinity of Io processes that are thought to be linked to Io's motion through Jupiter's plasma and magnetic field environment." Additional work is required to determine whether the beams play a role in producing some of the auroral emissions observed in Jupiter or if they are related to radio emissions that have been correlated with Io's orbital motion. "This is sufficient energy input into the Jovian atmosphere to produce visible auroral emissions," Williams said. Williams of the Applied Physics Laboratory of Johns Hopkins University and principal investigator on the energetic particle experiment, said the electron beams span the energy range of 15 kiloelectron volts to 190 kiloelectron volts and represent an energy deposition into Jupiter's atmosphere of up to 1 billion watts. The beams are similar to those that impinge on Earth's atmosphere to produce aurora and, also, positive ions and electrons in Earth's atmosphere.ĭr. In a related finding, the energetic particle detector on the spacecraft measured intense, bi-directional electron beams that are aligned with Galileo's magnetic field in Io's vicinity. Io's weak gravity field apparently permits the invisible gases emanating from the volcanoes to reach extraordinary heights far beyond the lower altitudes achieved by the dust and other volcanic ejecta that reflects sunlight and can be seen in images, Frank said. Torrence Johnson of NASA's Jet Propulsion Laboratory, Pasadena, CA, that invisible "stealth plumes" deliver volcanic gases to great heights above Io. The results may lend credence to previous theories proposed by Galileo Project Scientist Dr. "No one expected to see to see this at 900-kilometer altitude." The difference between what Pioneer saw and what Galileo has observed indicates that Io's atmosphere and ionosphere are variable and may grow and shrink with more or less volcanic activity, Frank said. A radio occultation by NASA's Pioneer 10 spacecraft in 1973 indicated ionospheric heights only 50 to 100 kilometers (about 30 to 60 miles) above the surface, he added. "Passage of the Galileo spacecraft through an ionosphere was not expected because images of the volcanic plumes previously taken with the Voyager spacecraft indicated that the plume heights extended only to a few hundred kilometers or less," said Frank. Instead of being swept away by Jupiter's rotating magnetosphere as anticipated, the ionized gases surprisingly remain with Io, he said. Frank of the University of Iowa and principal investigator on Galileo's plasma science experiment. Sensors on the spacecraft found a very dense region of ionized oxygen, sulfur and sulfur dioxide at 900 kilometers (550 miles) above Io that must be pumped into that region by Io's relentless volcanic activity, said Dr. ![]() The surprising discovery is being reported by Galileo scientists this week at a meeting of the American Astronomical Society's Division of Planetary Sciences being held in Tuscon, AZ, along with other Galileo results, including remarkable new images of the planet and its moons. The discovery suggests that Io's atmosphere is time variable and is made of volcanic gas lofted to very high altitudes.Īn ionosphere is a region of electrically charged gas that exists at the top of some planetary atmospheres. Scientists participating in NASA's Galileo mission have discovered that the Galileo spacecraft may have flown though a dense, high-altitude ionosphere during its encounter with Jupiter's volcanic moon Io last December.
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