| |
PD0RDD > NASA 21.09.98 18:33l 128 Lines 6060 Bytes #-10073 (0) @ WW
BID : 16662_PI8WNO
Read: GUEST
Subj: Nasa Information 152
Path: DB0AAB<DB0KFB<DB0CZ<DB0GE<DB0ZDF<DB0SRS<DB0MW<DB0ERF<DB0HSK<PI8DRS<
PI8DAZ<PI8GCB<PI8WNO
Sent: 980921/1407Z @:PI8WNO.#UTR.NLD.EU #:16662 [DeMeern] FBB5.15c $:16662_PI8W
From: PD0RDD@PI8WNO.#UTR.NLD.EU
To : NASA@WW
Onderwerp: Galileo Finds Jupiter's Rings Formed by Dust Blasted off Small Moons
Douglas Isbell
Headquarters, Washington, DC September 15, 1998
(Phone: 202/358-1753)
Jane Platt
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)
David Brand
Cornell University, Ithaca, NY
(Phone: 607/ 255-3651)
RELEASE: 98-167
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 five miles
(eight kilometers) 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 86,000 miles (143,000
kilometers). The ring system begins about 55,000 miles (92,000
kilometers) from Jupiter's center and extends to about 150,000
miles (250,000 kilometers) 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 Galileo website:
http://www.jpl.nasa.gov/galileo or at the Cornell website:
http://www.news.cornell.edu/releases/sept98/jupiter_rings.html
-end-
.
Greetings from Hans at Maarssenbroek ³~ The Netherlands
HomebBs : PI8WNO × .
E-Mail : pd0rdd@hj-lammers.demon.nl ××׶ Úп
Home Page : http://www.hj-lammers.demon.nl Ç×××׶ÚÏÍÏ¿
. ______ Ç×××׶³###³
System : Pentium 75 Ø ÚÄÄÄÊÊÊÊÊÊ¿Ç×××׶³###³ .
Modem : Tnc2nl . Öη ³ððððððððð³Ç×××׶³###³°° ³~
Progr : Sp 9.75 ³~ÖÊÊÊ· ³ððððððððð³Ç×××׶³###³°° ³ .
Tx/Rx : Kenwood TS-811e ³ÖÎÎÎÎη³ððððð²ß²ß²ß²ß²ß²ß²##³°ÛÛÛÛݳ³ ³~
Freq : 430.800 ܱ²Ü²ºãããã㺳ðððððºþÜþÜþÜþÜþÜþº##³°ÝÝÝÝÝ۲ܲ³Ü³Ü
ÛÛ²²±ººººººº³ððððÖÒÒÒÒÒÒ·þÜþÜþº##³°ÛÞÞÞݱ²²ÛÛ²²Û²Û²Ü
----------------------------------------------------
Read previous mail | Read next mail
| |
