BEIJING, May 12 (Xinhuanet) -- Magicians use smoke
and mirrors to create mystery, whereas Jupiter uses dust and shadow to conceal
the mystery of its faint rings.
Jupiter's rings are now known to be made mostly of
dark dust. They were discovered in 1979 by Voyager 1. Not until the Galileo
spacecraft, orbiting Jupiter from 1995 to 2003, did scientists realize the rings
were made of dust dispersed by meteoroids slamming into Jupiter's inner
moons.
Yet oddities remained that didn't match theoretical
predictions: The rings protrude beyond the orbit of the moon Thebe, and part of
the ring system is tilted compared to the main ring plane.
Alternating light and shadow cause these anomalies,
the new research finds.
"As they orbit about the planet, dust grains in the
rings alternately discharge and charge when they pass through the planet's
shadow," explained astronomer Douglas Hamilton of the University of Maryland.
"These systematic variations in dust particle electric charges interact with the
planet's powerful magnetic field."
Small dust particles are pushed beyond the ring's
expected outer boundary, and very small grains "even change their inclination,
or orbital orientation, to the planet," Hamilton said.
Hamilton and German colleague Harald Kruger studied
impact data on dust grain sizes, speeds and orbital orientations taken by
Galileo as it crossed the rings in preparation for its deliberate death plunge
into the planet. Kruger analyzed the new data set and Hamilton created computer
models that matched dust and imaging data on Jupiter's rings and explained the
observed eccentricities.
The new understanding can be applied to the rings of
Saturn, Uranus and Neptune, too, but the effects are more pronounced around
Jupiter, the researchers say.
(Agencies)
