Galileo Provides Many Discoveries In '98
JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011 From The "JPL Universe" By Jane Platt January 8, 1999
1998 was a tough year for those trying to keep up with all the discoveries from the Galileo Europa Mission, which has wrapped up the first half of its two-year extended mission. Following on the heels of the primary mission, Galileo Europa Mission has sent numerous batches of pictures and data back to Earth, helping scientists unlock the mysteries of Jupiter and its moons.
A series of additional Europa flybys in 1998 has provided information bolstering the premise of a liquid ocean beneath the icy moon's surface. The science community, the media and the public were enthralled this past March when pictures were unveiled from Galileo's closest Europa flyby in December 1997. The images, taken from only 200 kilometers (124 miles) above Europa, revealed rough, broadly scalloped icy cliffs on Europa as high as Mt. Rushmore, and a large, icy fracture large enough to be spanned by the Brooklyn Bridge. Also shown were impact crater Pwyll and the Conamara Chaos region, where icy plates on the surface have broken apart and moved around.
It appears Europa may not be the only Jovian moon with a possible ocean.
Data from Galileo's magnetometer instrument revealed evidence supporting the
premise of a liquid ocean under Callisto's surface. This data indicated that
electrical currents flowing in a shell near Callisto's surface are causing
changes observed in Jupiter's magnetic field during Galileo's flybys. A
salty liquid layer has been suggested as a likely candidate for creating the
electrically conducting shell.
Scientists are re-thinking their ideas about Callisto's interior structure,
based on new data from Galileo. While previous data indicated that
Callisto's interior was totally undifferentiated, new information suggested
Callisto has an interior that does not vary dramatically, but is not
completely uniform.
Io, Ganymede and Europa, on the other hand, have differentiated structures with separated layers. The Galileo data suggest that Callisto may have been less affected by gravitational squeezing and subseq uent heating than Io, Ganymede and Europa.
New Galileo pictures showed closeup views of a fault on Europa as long as
California's portion of the infamous San Andreas. Called Astypalaea Linea,
it is a strike-slip fault, meaning it has two crustal blocks that move
horizontally past one another, some what like two opposing lanes of traffic.
The Galileo images show that about 50 kilometers (30 miles) of movement has
taken place along the fault. While the Galileo pictures captured a
290-kilometer-long (180-mile) portion of the fault, scientists calculat e
its full length at about 810 kilometers (more than 500 miles).
Jupiter's fiery moon Io turned out to be even hotter than scientists had known. Galileo's camera captured images of dozens of volcanic vents on Io, where lava is hotter than any known surface temperatures on any planetary body in the solar system. At one of these volcanic vents, called Pillan Patera, the lava temperature may be 2,000 Kelvin (3,140 degrees Fahrenheit). Such high temperatures are not known to have occurred on Earth for billions of years. Galileo Project Scientist Dr. Torrence Johnson said t his data indicates high-temperature eruptions are a basic, common part of Io's volcanic processes.
Recent images of Ganymede, the largest moon of any planet in the solar system, revealed impact craters with unusual pedestals, dark ejecta haloes, evidence of tectonic activity and possible signs of icy volcanic flows. A crater chain appeared to have been caused by impacts from a broken-up comet, similar to the 1994 Shoe-maker-Levy impact on Jupiter.
Scientists now know much more about the origin of Jupiter's rings, thanks to recent Galileo images. The huge planet's swirling ring system is formed by dust kicked up as interplanetary meteroids smash into Jupiter's four small inner moons. And the outermost ring, previously believed to be a single feature, was found to be two rings, one embedded within the other.
New information gathered by Galileo, the Hubble Space Telescope and ground-based observations revealed that two of Jupiter's giant, swirling "white oval" storms merged early in 1998 to form a larger white oval as big as Earth. A colorful image of aurora on Io was also released.
Galileo continues under the leadership of Project Manager Jim Erickson, who
assumed the post after the previous project manager, Bob Mitchell, became
Cassini program manager last June. In 1999, Galileo will wrap up its series
of Europa flybys on Jan. 31, then it will fly by Callisto four times before
lowering its orbit for two Io flybys, as long as the spacecraft remains
healthy.
Additional information and images may be found at the following websites:
Galileo has been in orbit around Jupiter and its moons for the past three years. Its primary mission ended in December 1997, and the spacecraft is currently in the midst of a two--year extension known as the Galileo Europa Mission. Galileo is managed by JPL for NASA's Office of Space Science, Washington, DC. JPL is a division of Caltech, Pasadena, CA.
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