Robot Explorers: US Unmanned Space Missions

Robot Explorers: US Unmanned Space Missions: page 18

This image of Europa and an enlargement of the Thrace region gives visual evidence of the dramatic advance in our knowledge of Jupiter's second Galilean satellite due to the Galileo mission.

Prior to the Galileo mission, scientists' knowledge of Europa was simply a small ice-covered moon with an exceptionally bright surface covered by faint curved and linear markings. Now, scientists see evidence of a young and thin, cracked and ruptured ice shell, probably moving slowly over the surface of a briny ocean that is 62 miles or more deep. Europa has become recognized as a potential habitat for extraterrestrial life and is now an important target for future solar system exploration.

The detection of very high temperature volcanism - hotter than any terrestrial lavas currently erupting - is one of the most spectacular discoveries by the Galileo mission at Io. The images are of an area called Tvashtar and show curtains of lava fountains erupting on the surface. They were taken by the Galileo spacecraft on November 26, 1999. The active region is approximately 15.5 miles long and 0.6 miles high. The radiant energy emitted from the lava curtain was so intense that it overpowered the camera's detector and it is registered only in white.

The first discrete ammonia ice cloud positively identified on Jupiter is shown in this false-color image that was taken with the Near-infrared Mapping Spectrometer on the NASA's Galileo spacecraft on June 26, 1996. Ammonia ice (light blue) is shown in clouds to the northwest (upper left) of the Great Red Spot. This unusual cloud, inside the turbulent wake region of the Great Red Spot, is produced by powerful updrafts of ammonia--laden air from deep within Jupiter's atmosphere. These updrafts are generated by the turbulence induced in Jupiter's massive westward-moving air currents by the nearby Great Red Spot. At over 12,400 miles wide, the Great Red Spot, which has existed for at least 300 years, is the oldest and largest weather system in our solar system.

This mosaic of two images shows an area within the Valhalla region on Jupiter's moon Callisto and illustrates one of the most significant discoveries of Galileo. There is an unexpected absence of small craters and clear evidence in the ragged rims of the craters of an erosion process that is believed to be due to sublimation of volatiles from the surface ice. North is to the top of the mosaic and the Sun illuminates the surface from the left. The mosaic covers an area approximately 20 miles across. Scientists believe Valhalla is the result of a large impact early in the history of Callisto.

The Galileo spacecraft's 14-year odyssey came to an end on Sunday, Sept. 21, 2003, when the spacecraft passed into Jupiter's shadow then disintegrated in the planet's dense atmosphere. After 14 years of flight time and 8 years of service in the Jovian system, Galileo's mission was terminated by sending the probe into Jupiter's crushing atmosphere at a speed of nearly 30 miles per second to avoid any chance of it contaminating local moons with bacteria from Earth. Of particular concern was the ice-crusted moon Europa, which, thanks to Galileo, scientists now suspect harbors a salt water ocean—and possibly microbial life—beneath its surface.

For more information on Galileo visit http://galileo.jpl.nasa.gov/

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	Copyright ©2004 Colleen Gino	Images and content courtesy JPL and NASA.