Using an innovative camera on NASA's Cassini
spacecraft, scientists have captured images of a radiation
belt inside the rings of Saturn and have the clearest
picture yet of the planet's giant magnetosphere, according
to a mid-year report of the spacecraft published Feb. 25 in
the journal Science.
The Cassini spacecraft entered Saturn's orbit in July
2004, kicking off a four-year study of the sixth planet
from the sun. Among the 12 science instruments on the
spacecraft is the APL-developed
Magnetospheric
Imaging Instrument, or MIMI, which scientists are using
to study the energetic charged particle environment at
Saturn and obtain images of the ringed planet's
magnetosphere.
"Every time we fly a new instrument in space, it
reveals new vistas of whatever object we happen to be
studying," said APL's
Stamatios "Tom" Krimigis, principal investigator for the
MIMI experiment.
This time, Krimigis said, the MIMI instrument has
enabled scientists to "visualize the invisible"--to "see"
the plasma and radiation belts in Saturn's environment in
an image; to discover that the belts are more intense on
the night-side of the planet; to determine that there is an
unexpected radiation belt inward of the "D" ring, the
fourth major ring closest to the tenuous upper atmosphere
of the planet; and to confirm that there is a virtual soup
of ions that derive from the dissociation of water, most
likely due to radiation impacting the rings.
These images were captured during Saturn orbit
insertion with MIMI's Ion and Neutral Camera, or INCA,
which measures the three-dimensional distribution,
velocities and rough composition of magnetospheric and
interplanetary ions for regions in which the energetic ion
fluxes are very low. It also provides a global view of the
energetic neutral emission of hot plasmas in the Saturnian
magnetosphere, measuring the composition and velocities of
those energetic neutrals for each image pixel.
"By detecting various energetic particles and
discriminating among them according to energy and mass, the
camera is able to obtain remote images of the global
distribution of these particles," said Donald Mitchell of
APL, who leads the camera science team.
Ed Roelof of APL, a co-investigator on the MIMI team,
said, "Using INCA, we also discovered a radiation belt in a
place where no spacecraft can go--inside the planet's
rings. We never knew this belt existed, but we saw it and
were able to determine some of its properties and
characteristics."
The properties of the main radiation belts are perhaps
among the more significant of the findings, said Doug
Hamilton of the University of Maryland, College Park, who
led the instrument team measuring the composition. "It's
comprised mostly of oxygen and water products," he said.
"That is most likely the result of the bombardment of the
planet's rings and the icy moons by the radiation trapped
in Saturn's magnetic field. And by this bombardment, the
water is released and it becomes charged."
Krimigis said that the ability to visualize a planet's
magnetosphere will enable scientists to better monitor
space weather. "This will benefit science and, in the case
of Earth, may lead to space weather forecasts that will
give advance warning of electromagnetic storms, which in
the past have disrupted communications and crippled
electrical power grids."
In addition to Krimigis, Mitchell and Roelof, research
team members at APL and co-authors on the Science paper,
are Stefano Livi, Barry Mauk, Christopher Paranicas, Pontus
Brandt, Andrew Cheng, Teck Choo, John Hayes, Stephen
Jaskulek, Edwin Keath, Martha Kusterer, David LaVallee,
Richard McEntire, Joachim Saur, Franklin Turner and Donald
Williams.
The
Cassini-Huygens mission is a cooperative project of
NASA, ESA and the Italian Space Agency. The Jet Propulsion
Laboratory, a division of the California Institute of
Technology in Pasadena, manages the mission for NASA. The
MIMI team includes investigators and expertise from APL;
the University of Maryland, College Park; University of
Kansas, Lawrence; University of Arizona, Tucson; Bell
Laboratories, Murray Hill, N.J.; the Max Planck Institute
for Solar System Research, Lindau, Germany; and the Centre
d'Etude Spatiale des Rayonnements in Toulouse, France.
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