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Science Forum Index » Astro Forum » Scientists Find Rings of Jupiter Are Shaped in Shadow (Forwarded)
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| Andrew Yee |
 Posted: Fri May 02, 2008 12:50 pm |
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Office of University Communications
University of Maryland
Contacts:
Lee Tune, 301 405 4679
For Immediate Release: April 30, 2008
Scientists Find Rings of Jupiter Are Shaped in Shadow
COLLEGE PARK, Md. -- Scientists from the University of Maryland and the
Max-Planck Institute for Solar System Research in Germany appear to have
solved a long-standing mystery about the cause of anomalies in Jupiter's
gossamer rings.
In a new study published in the May 1 issue of Nature, they report that a
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, result 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. 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."
Hamilton and German co-author Harald Krüger 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, as part of its deliberate maneuvering for a death plunge into
the planet. Krüger 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 Krüger.
According to Hamilton, the mechanisms identified in this paper affect the
rings of any planet in any solar system, but the effects may not be as
evident as it is at Jupiter. "The icy particles in Saturn's famous rings
are too large and heavy to be significantly shaped by this process, which
is why similar anomalies are not seen there," he said. "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."
Jupiter, Galileo and the Mystery of the Rings
Jupiter, the fifth planet from the Sun, has 63 known moons. 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
(closest to farthest). 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.
Italian scientist Galileo Galilei was the first to discover that Jupiter
had moons. Galileo first observed the planet's four largest moons in 1610.
On December 7, 1995 NASA's Galileo spacecraft reached Jupiter and began
the first of 35 orbits around the planet. Over seven years the spacecraft
took some 14,000 images of Jupiter, its moons and rings. It also released
a probe that sent back the information on the planet's atmosphere. On
September 21, 2003 the Galileo spacecraft was put into a controlled dive
to end its mission, by plummeting through Jupiter's atmosphere. In
addition to its imaging instruments, the spacecraft carried a
supersensitive dust detector, which registered thousands of impacts from
dust particles on its way through Jupiter's ring system in 2002 and 2003.
The Thebe extension was one of the many new discoveries made by the
Galileo spacecraft.
The overall Galileo mission was managed by NASA's Jet Propulsion
Laboratory (JPL), which also built its main (orbiter) spacecraft.
Click to view animations by Hamilton and colleagues showing orbits and
relative speeds around the sun of Jupiter and the other planets, and then
click on Jupiter in the list of planets to see it the orbiting of its 64
moons,
http://janus.astro.umd.edu/SolarSystems/
IMAGE CAPTIONS:
[Image 1:
http://www.newsdesk.umd.edu/scitech/Jupiter/jupiter_rings.jpg (14KB)]
Jupiter's rings consist of bands of widely scattered dust particles
generated by the impact of space debris into the planet's 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. However,
a faint outward protrusion of dust (not show here) extends beyond the
orbit of Thebe.
Courtesy: NASA
[Image 2:
http://www.newsdesk.umd.edu/scitech/Jupiter/rings_edgeview.jpg (24KB)]
Jupiter's gossamer rings as seen by Galileo from a location near the
planet's equatorial plane (false colour). In this edge on view Jupiter is
out of the image to the left and the ring system can be seen in four
distinct components: (1) the main ring (in white) projecting inward from
the two moonlets Metis and Adrastea, (2) the vertically extended halo
(white) with thickness 0.1RJ (RJ571,492km) interior to the main ring, (3)
a gossamer ring associated with the satellite Amalthea (small yellow
rectangle), and (4) an even fainter ring associated with Thebe (large red
rectangle). White crosses mark the extremes of the radial and vertical
orbital motions of the two moons. The thicknesses of the two outer rings
exactly match the vertical excursions of the two source satellites, and
ring material appears to extend primarily inward from all four moons. The
Thebe extension is the faint material (in blue) located outside Thebe's
orbit.
From the article: The sculpting of Jupiter's gossamer rings by its shadow
Douglas P. Hamilton & Harald Krüger Nature 453, 72-75(1 May 2008)
doi:10.1038/nature06886 |
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