[meteorite-list] Re: Galileo Discovers Objects Near Jupiter's Inner Moon Amalthea

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:10:07 2004
Message-ID: <200304102024.NAA06865_at_zagami.jpl.nasa.gov>

>JPL engineers Paul Fieseler and Shadan Ardalan reported the findings
>to the International Astronomical Union. The star tracker saw nine
>flashes during the flyby, but two may be duplicate sightings.
>
>"It is likely that these bodies have either been gravitationally
>captured into an orbit near Amalthea or have been split off of the
>moon as a result of past collisions," Fieseler said.

Since Amalthea is the source of one of Jupiter's rings, I think
what is being seen is ring particles. See the 1998
press release below.

Ron Baalke


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Contact at Cornell: David Brand (607) 255-3651

FOR IMMEDIATE RELEASE September 15, 1998

GALILEO FINDS JUPITER'S RINGS FORMED BY DUST BLASTED OFF SMALL MOONS

Jupiter's intricate, swirling ring system is formed by dust kicked up as
interplanetary meteoroids smash into the giant planet's four small inner
moons, according to scientists studying data from NASA's Galileo spacecraft.
Images sent by Galileo also reveal that the outermost ring is actually two
rings, one embedded within the other.

The findings were announced today by scientists from Cornell University,
Ithaca, NY, and the National Optical Astronomy Observatories (NOAO), Tucson,
AZ, at a news briefing held at Cornell.

"We now know the source of Jupiter's ring system and how it works," said
Cornell astronomer Dr. Joseph Burns, who reported on the first detailed
analysis of a planet's ring system, along with Maureen Ockert-Bell and Dr.
Joseph Veverka of Cornell, and Dr. Michael Belton of NOAO.

"Rings are important dynamical laboratories to look at the processes that
probably went on billions of years ago when the Solar System was forming
from a flattened disk of dust and gas," Burns explained. Furthermore,
similar faint rings probably are associated with many small moons of the
Solar System's other giant planets. "I expect we will see similar processes
at Saturn and the other giant planets," Burns said.

In the late 1970s, NASA's two Voyager spacecraft first revealed the
structure of Jupiter's rings: a flattened main ring and an inner, cloud-like
ring, called the halo, both composed of small, dark particles. One Voyager
image seemed to indicate a third, faint outer ring. New Galileo data reveal
that this third ring, known as the gossamer ring because of its
transparency, consists of two rings. One is embedded within the other, and
both are composed of microscopic debris from two small moons, Amalthea and
Thebe.

"For the first time we can see the gossamer-bound dust coming off Amalthea
and Thebe, and we now believe it is likely that the main ring comes from
Adrastea and Metis," Burns said. "The structure of the gossamer rings was
totally unexpected," Belton added. "These images provide one of the most
significant discoveries of the entire Galileo imaging experiment."

Galileo took three dozen images of the rings and small moons during three
orbits of Jupiter in 1996 and 1997. The four moons display "bizarre surfaces
of undetermined composition that appear very dark, red and heavily cratered
from meteoroid impacts," Veverka said. The rings contain very tiny particles
resembling dark, reddish soot. Unlike Saturn's rings, there are no signs of
ice in Jupiter's rings.

Scientists believe that dust is kicked off the small moons when they are
struck by interplanetary meteoroids, or fragments of comets and asteroids,
at speeds greatly magnified by Jupiter's huge gravitational field, like the
cloud of chalk dust that rises when two erasers are banged together. The
small moons are particularly vulnerable targets because of their relative
closeness to the giant planet.

"In these impacts, the meteoroid is going so fast it buries itself deep in
the moon, then vaporizes and explodes, causing debris to be thrown off at
such high velocity that it escapes the satellite's gravitational field,"
Burns said. If the moon is too big, dust particles will not have enough
velocity to escape the moon's gravitational field. With a diameter of just
eight kilometers (five miles) and an orbit that lies just at the periphery
of the main ring, tiny Adrastea is "most perfectly suited for the job."

As dust particles are blasted off the moons, they enter orbits much like
those of their source satellites, both in their size and in their slight
tilt relative to Jupiter's equatorial plane. A tilted orbit wobbles around a
planet's equator, much like a hula hoop twirling around a person's waist.
This close to Jupiter, orbits wobble back and forth in only a few months.

Jupiter's diameter is approximately 143,000 kilometers (86,000 miles). The
ring system begins about 92,000 kilometers (55,000 miles) from Jupiter's
center and extends to about 250,000 kilometers (150,000 miles) from the
planet.

Galileo has been orbiting Jupiter and its moons for 2 1/2 years, and is
currently in the midst of a two-year extension, known as the Galileo Europa
Mission. JPL manages the Galileo mission for NASA's Office of Space Science,
Washington, DC. JPL is a division of Caltech, Pasadena, CA. The new images,
and further information on this discovery and the Galileo mission, are
available on the Internet at the following websites:

http://www.jpl.nasa.gov/galileo
http://photojournal.jpl.nasa.gov
http://www.news.cornell.edu/releases/sept98/jupiter_rings.html
Received on Thu 10 Apr 2003 04:24:45 PM PDT