Anomalies in Jupiter's rings results from interplay of shadow and sunlight

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Washington, May 1 : Scientists have solved a long-standing mystery about the cause of anomalies in Jupiter's rings, attributing them to the interplay of shadow and sunlight on dust particles that make up the rings.

This was reported by scientists from the University of Maryland and the Max-Planck Institute for Solar System Research in Germany.

The dust forming Jupiter's faint rings is produced when bits of space debris smashes into the small inner moons Adrastea, Metis, Amalthea and Thebe. This dust is organized into a main ring, an inner halo, and two fainter and more distant gossamer rings.

The rings largely are bounded by the orbits of these four moons, but a faint outward protrusion of dust extending beyond the orbit of Thebe has, until now, mystified scientists.

According to the scientists, the faint extension of the outermost ring beyond the orbit of Jupiter's moon Thebe, and other observed deviations from an accepted model of ring formation, results from the interplay of shadow and sunlight on dust particles that make up the rings.

"It turns out that the outer ring's extended boundary and other oddities in Jupiter's rings really are made in the shade," said Douglas Hamilton, a professor of astronomy at the University of Maryland.

As they orbit about the planet, dust grains in the rings alternately discharge and charge when they pass through the planet's shadow, according to Hamilton.

"These systematic variations in dust particle electric charges interact with the planet's powerful magnetic field. As a result, small dust particles are pushed beyond the expected ring outer boundary, and very small grains even change their inclination, or orbital orientation, to the planet," he said.

Hamilton and German co-author Harald Kruger studied for the first time new impact data on dust grain sizes, speeds, and orbital orientations taken by the spacecraft Galileo during its traversal of Jupiter's rings in 2002-2003.

Kruger analyzed the new data set and Hamilton created elaborate computer models that matched dust and imaging data on Jupiter's rings and explained the observed eccentricities.

"Within our model we can explain all essential structures of the dust ring we observed," said Kruger.

"Our findings on the effects of shadow may also shed some light on aspects of planetary formation because electrically charged dust particles must somehow combine into larger bodies from which planets and moons are ultimately formed," said Hamilton.

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