New results from the Cassini mission indicate the spacecraft was pelted with
sporadic bursts of interplanetary dust as it approached Saturn last year,
according to a University of Colorado at Boulder space scientist.

Mihaly Horanyi of CU-Boulder’s Laboratory for Atmospheric and Space Physics said
the dust particle bursts grew more frequent and intense as the Cassini
spacecraft closed in on the planet from 40 million miles away in early 2004.
Horanyi, also a CU-Boulder physics professor, said the dust might have escaped
into space from the planet’s outer “A” ring or perhaps its icy moons, Dionne and

A paper on the subject was published in the Jan. 20 issue of the journal Nature.
In addition to Horanyi, authors include Sascha Kempf, Ralf Srama, Stefan
Helfert, Georg Moragas-Klostermeyer and Eberhard Grun of Germany’s Max Planck
Institute, and Marcia Burton and Mou Roy of NASA’s Jet Propulsion Laboratory.

Prior to 1993, researchers believed such interplanetary dust particles were made
up of primitive material originating from interstellar space, asteroid
collisions or from comets whizzing through the solar system, Horanyi said.

But in 1993, Horanyi and colleagues found that peculiar bursts of microscopic
dust observed streaming from the Jupiter region by the Ulysses spacecraft were
emanating from the volcanic plumes of Io, a moon of Jupiter. “That was the first
indication that dust can escape from planetary systems,” he said.

The dust particles escaping from the Saturn system also are microscopic in size,
ranging from one-tenth of a micron to one-hundredth of a micron, he said.

“Grains larger than that would be dominated by the gravity of the planet, while
smaller grains would be dominated by the electromagnetic fields. Only those
within these size limits can escape the system.”

The dust detector aboard Cassini collects electrical signals from each grain of
dust it traps, allowing scientists to infer the mass and speed of the particles,
he said. “The energetics of the dust particles indicate that the A ring of
Saturn is a good candidate for the origin of the dust,” Horanyi said.

The burst-like phenomenon of dust grains — which were traveling at an
astounding 60 miles per second — was due to the planet’s magnetic field and the
solar wind “bending” the dust trajectories as they streamed from the Saturn
system, he said. “The dust is probably coming from the Saturn system at a fairly
constant rate, but the spacecraft was not always in the right place to detect
it,” he said.

Horanyi also is a member of a CU-Boulder team that has designed and built a dust
detector to fly on NASA’s 2006 New Horizons mission to Pluto. The New Horizons
instrument, designed and built primarily by students, is expected to provide new
information on the structure and early formation of the solar system.

An identical instrument also built by LASP will be launched in September 2006 on
the Aeronomy of Ice in the Mesosphere, or AIM, mission to monitor the dust
influx into Earth’s atmosphere, he said.