Andrew Yee[_1_]
May 2nd 08, 06:43 PM
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. " 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 Kruger 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.
Kruger 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 Kruger.
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 Kruger Nature 453, 72-75(1 May 2008)
doi:10.1038/nature06886
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. " 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 Kruger 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.
Kruger 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 Kruger.
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 Kruger Nature 453, 72-75(1 May 2008)
doi:10.1038/nature06886