Contact: Jane Platt

April 28, 1999

Galileo Spacecraft Beams Pictures Back to Earth

NASA's Galileo spacecraft is once again beaming back to Earth pictures and other scientific information collected during its January 31 flyby of Jupiter's icy moon Europa. Data transmission from the spacecraft was on hold for three weeks while the Sun was positioned between Earth and Jupiter. During that time, the Sun interfered with Galileo's radio signal and made communications difficult.

There was a bright side to this situation, however, because it enabled scientists to study the way the solar wind distorted Galileo's radio signal. This helped them learn more about that powerful wind, which consists of electrified particles emitted by the Sun. The solar wind has a very strong effect on Earth and all other objects in our solar system.

Galileo will finish transmitting its latest batch of Europa data, which had been stored on the spacecraft's tape recorder, on April 30. This information includes observations that tell scientists more about the surface composition and texture of Jupiter's largest moon, Ganymede. Other observations help differentiate between possible crystalline forms of water ice on Europa. The shape of the crystals relates to the temperature at which they formed, and a certain form of ice would indicate that it solidified when liquid water spewed from a geyser and froze. This might be yet another hint of an ocean beneath Europa's icy crust.

Galileo's flight team is preparing for a May 5 flyby of Jupiter's moon Callisto by updating software for the spacecraft's computer. The idea is to prepare the spacecraft for any false power reset signals, like those that occurred twice last year. The software would allow the spacecraft to recover by itself and continue with its pre-programmed schedule of activities. Engineers believe false reset signals are triggered when debris accumulates in the electrical connections between the spacecraft's spinning and non-spinning sides and causes an electrical short. The debris may come from wear and tear on the slip rings that connect the two sides.

Galileo has been orbiting Jupiter and its moons for nearly 3-1/2 years, gathering pictures and other information. The spacecraft is currently more than halfway through a two-year extended Galileo Europa Mission, a follow-on to the primary mission that ended in December 1997. The mission is managed by JPL for NASA's Office of Space Science, Washington, D.C.