A team led by the University of Colorado at Boulder has found new evidence that a faint, doughnut-shaped ring of interplanetary and interstellar dust some 700,000 miles in diameter is orbiting Jupiter.
Voyager 2 detected an uneven dust ring around Jupiter in 1979 ranging from 200 to 3,000 miles in diameter that was created by the collisions of small moonlets with micro-meteoroids in the Jovian system, said University of Colorado at Boulder researcher Joshua Colwell. But the newly identified ring of dust originating from beyond the Jovian system appears to be much larger, more sparse and, thus far, unique in the solar system.
Surprisingly, most of the interstellar and interplanetary dust particles appear to be in a "retrograde" orbit 聳 that is, moving in the opposite direction of the rotating planet and its moons, said Colwell, a research associate at CU-Boulder聮s Laboratory for Atmospheric and Space Physics. The reason for the backward orbit of the tiny particles is not yet clear, he said.
The evidence for the new ring聮s existence comes from computer simulations that correlate with data collected by a dust detector aboard NASA聮s Galileo spacecraft now orbiting Jupiter and its moons. "We believe that the Galileo spacecraft has detected this ring by capturing some of its dust," Colwell said.
A paper on the subject by Colwell, LASP research associate Mihaly Horanyi and planetary scientist Eberhard Grun of the Max Planck Institute for Astrophysics in Heidelberg was published in the April 3 issue of Science.
Interstellar and interplanetary dust grains between about .6 micrometers and 1.4 micrometers are captured by Jupiter聮s magnetosphere, or area of magnetic influence, according to the study. Such particles are smaller than the diameter of a human hair and about the size of smoke particles.
"If these particles are just the right size, they lose energy to the magnetosphere and are captured in the ring," he said. Grains smaller than that are deflected away from the magnetosphere while larger grains retain enough of their energy to avoid capture by the magnetosphere.
The dust grains in the new class of dust ring are scarce enough that a photon of light sent through the faint ring would have less than one in a billion chance of hitting a dust grain. "I suspect we may wind up seeing something similar at Saturn," said Colwell. Launched in 1997, the Cassini spacecraft will reach the ringed planet in 2004.
The bowl-shaped metal dust detector on Galileo has a charged grid over its top. As the detector sweeps back and forth through space, tiny specks of dust that hit the bowl vaporize, creating a small cloud that is detected by the grid. The direction and motion of the detector can tell scientists the direction and velocity of the interplanetary and interstellar dust rings.
Although dust always is entering the solar system, it also is escaping, said Colwell. Research by CU聮s Horanyi in 1993 using Ulysses spacecraft data indicated that some of the microscopic dust particles originating from volcanoes on Jupiter聮s moon, Io, were traveling in streams at more than 100 miles per second. This allowed them not only to escape Jupiter聮s magnetic grip but to escape from the solar system as well, said Colwell.
Horanyi also has predicted that the violent collision between comet Shoemaker-Levy and Jupiter in 1993 should form a new ring of dust around the planet by 2003.
Colwell and a group of eight present or former students designed and built a payload that will launch on NASA聮s space shuttle Columbia April 16 to study the collisions of dust particles in space. The microgravity provided by the shuttle will allow them to analyze the gentle collisions of dust grains in space, helping them to better understand the life cycle of such particles.