PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
CONTACT: Mary Beth Murrill
FOR IMMEDIATE RELEASEJune 24, 1996
GALILEO READIES FOR CLOSE FLYBY OF JUPITER'S BIGGEST MOON
Now residing in orbit around Jupiter, NASA's Galileo spacecraft
is primed for its first close flyby of Jupiter's largest moon,
Ganymede, at 6:29 Universal Time on June 27 (11:29 p.m. Pacific
Daylight Time on June 26).
Equipped with 10 scientific instruments, Galileo will fly just
844 kilometers (524 miles) above Ganymede's surface to provide
detailed images and other information ever obtained about the icy
satellite. Images and other data gathered by the spacecraft will
back to Earth in the hours and months following the flyby.
On June 23, Galileo's particle detectors and magnetic fields
instruments began making nearly continuous measurements as the
spacecraft approached Ganymede. Its optical instruments will
shortly begin their periodic observations, including the first
round of picture-taking (other
than engineering images taken for navigation purposes) since
months before the spacecraft entered orbit around Jupiter on
If spacecraft operations near Ganymede and the subsequent
transmission to Earth of initial science data occur as planned,
selected images of Ganymede taken by Galileo will be released in
a televised news conference at the Jet Propulsion Laboratory,
tentatively scheduled for July
With a 5,262-kilometer (3,269-mile) diameter, Ganymede is the
largest moon in the solar system -- bigger than Mercury and about
three-quarters the size of Mars. It possesses a variety of
familiar Earthlike geologic formations including craters and
basins, grooves and mountains. The bulk of the satellite is about
half water ice and half rock.
Portions of its surface are relatively bright, clean ice while
the other regions are covered with darker "dirty" ice. The darker
areas appear to be ancient and heavily cratered, while the
lighter regions display evidence of tectonic activity that may
have broken up the icy crust. A thin layer of ozone has been
found in Ganymede's surface by astronomers.
Galileo will return high-resolution images showing features on
Ganymede as small as 10 meters (about 33 feet) across.
Instruments on board will assess Ganymede's surface chemistry and
search for signs of an atmosphere around the big moon.
Measurements will be made to characterize Ganymede's gravity
field and to determine if it possesses a magnetic field.
In the days just before and after the Ganymede flyby, Galileo's
other studies include a search for auroral activity on Jupiter's
nightside and observations of other Jovian moons: Io, Europa and
Callisto. The "Io torus," a hot, doughnut-shaped ring of charged
particles swirling about Jupiter at Io's distance, will be
another target of study, as will Jupiter's Great Red Spot.
Galileo's Ganymede encounter marks the start of a steady stream
of data to be returned to Earth by Galileo's instruments
throughout the course of its two-year tour of the Jovian system,
which continues through December 1997. Beginning in July, data
return will include an average of two to three images per day.
The remainder Galileo's mission is to complete 11 orbits of
Jupiter, conducting multiple close flybys of the moons Ganymede,
Europa and Callisto, with numerous, more distant studies of the
moon Io also scheduled throughout the tour. Studies of Jupiter
itself are planned throughout the tour, and nearly continuous
studies of Jupiter's enormous radiation and magnetic fields will
The fifth planet from the Sun is known primarily for the banded
appearance of its upper atmosphere and its centuries-old Great
Red Spot, a massive, hurricane-like storm as big as three Earths.
Jupiter generates the biggest and most powerful planetary
magnetic field, and it radiates
more heat from internal sources than it receives from the Sun.
Given its large size and its many natural satellites, Jupiter is
often described as a miniature solar system. Jupiter has 318
times more mass and 1,400 times more volume than Earth, but is
only one-fourth as dense, since it is composed primarily of
hydrogen and helium. It is orbited by at least 16 moons (and
Galileo -- its first artificial satellite).
The 2,223-kilogram (2-1/2-ton) Galileo orbiter spacecraft was
launched aboard Space Shuttle Atlantis on Oct. 18, 1989. It
carries the most capable payload of scientific experiments ever
sent to another planet.
Communications to and from Galileo are conducted through NASA's
Deep Space Network, using tracking stations in California, Spain
and Australia. A combination of new, specially developed software
for Galileo's onboard computer and improvements to ground-based
signal receiving hardware in the Deep Space Network have enabled
the spacecraft to accomplish at least 70 percent of its original
mission science goals using only its small, low-gain antenna,
despite the failure of its high-gain antenna to unfurl properly
in April 1991.
NASA's Jet Propulsion Laboratory, Pasadena, CA, built the Galileo
orbiter spacecraft and manages the overall mission. Galileo's
atmospheric probe was managed by NASA's Ames Research Center,
Mountain View, CA.
Additional information on the Galileo mission and its results can
be found on the World Wide Web at:
Note to Editors: A NASA Video File to accompany this news release
will be aired on NASA Television today at 2, 4, 7 and 9 p.m. PDT.
NASA Television is broadcast on Spacenet 2, transponder 5,
channel 9, C band, located at 69 degrees west longitude,
horizontal polarization, frequency 3880.0 megahertz, audio 6.8
megahertz. A computer-generated rendering to accompany this news
release is available
from JPL's Public Information Office, (818) 354-5011.