CU Astronomers Probe Energy Source of Jupiter's Massive Charged-Particle Ring

July 29, 1997

A charged-particle ring encircling Jupiter that glows with a power greater than all the electricity generated on Earth seems to be fueled both by its volcanically active moon, Io, and an unknown source further out in Jupiter’s environment.

University of Colorado at Boulder astronomers Nicholas Schneider and Michael Kueppers said the doughnut-shaped ring known as the Io torus, which is almost 10 times larger than Jupiter itself, has puzzled astronomers since its discovery in 1976. The CU-Boulder researchers, along with astronomer Melissa McGrath of the Space Telescope Science Institute in Baltimore, have been making observations of the bizarre ring with the Hubble Space Telescope.

Since most of the energy in the ring is radiated by ultraviolet light invisible from Earth, the team is using a spectrograph aboard the orbiting telescope that can measure UV emissions from above Earth’s atmosphere. The researchers are using the instrument to map the shape of the peculiar torus, which reaches temperatures over 100,000 degrees Fahrenheit as it rotates with the giant planet.

The researchers are particularly interested in pinpointing the ring’s energy sources and understanding why half of the ring consistently glows more brightly than the other half. “The brightness difference from one side of the torus to the other is so large that an extra energy source must be required to keep the brighter side glowing,” said Schneider of CU-Boulder’s Laboratory for Atmospheric and Space Physics.

Much of the material in the charged ring is believed to originate from active volcanoes on Io that spew sulfur dioxide, which is broken into sulfur and oxygen ions that are captured by Jupiter’s massive magnetic field.

“We know the ring is spawned by Jupiter's volcanically active moon Io,” said Schneider. “Thanks in part to Io's low gravity, its atmosphere escapes at the rate of about one ton per second, and the escaping particles are ionized and swept up by Jupiter's strong magnetic field.”

Even though the toris is about 600,000 miles across, “it has such a low density that all the particles would fit inside Fenway Park if compressed to solid form,” said Schneider.

If some of the energy present in the Io torus is arriving from a source elsewhere in Jupiter’s environment, NASA’s Galileo spacecraft now orbiting the planet may eventually be able to identify it, said Schneider. The spacecraft’s instruments include an ultraviolet spectrometer and an extreme UV spectrometer from CU-Boulder.

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