NASA's Galileo spacecraft soars above Jupiter's volcanic moon Io in this artist's impression. Photo: NASA/JPL

In a relatively quiet week, Galileo's activities are dedicated to the return of science data stored on its onboard tape recorder. The data were acquired during the spacecraft's February flyby of Jupiter's volcanic moon Io. The data returned this week are from a second pass through the data stored on the tape recorder. This additional pass provides Galileo's science community the opportunity to return new data, replay data lost in previous transmissions, and/or reprocess and compress data for transmission with different parameters.

This week's playback schedule contains two regions on Io observed by both the Solid-State Imaging camera (SSI) and the Near-Infrared Mapping Spectrometer (NIMS). The first is Chaac Patera, a new hot spot identified in data acquired by Galileo in November 1999. Chaac Patera includes one of the areas on Io that are informally known as Io's golf courses because of their greenish color. The second region that was jointly observed is the Prometheus volcanic region.

NIMS then returns a mosaic of several different volcanic regions on Io's surface. SSI follows suit with the return of two observations. In the first, SSI returns parts of three images, taken through different color filters, of Tvashtar Catena, a chain of giant calderas found in Io's northern hemisphere. One of these calderas was seen to be erupting a curtain of lava 1.5 kilometers (0.9 miles) high and 20 kilometers (12.4 miles) long during a previous encounter. SSI then returns parts of an observation of the Zal volcanic region.

Throughout the week, the Fields and Particles instruments continue to return parts of a high resolution recording of the plasma, dust, and electric and magnetic fields surrounding Io. The Fields and Particles instruments are comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument.

On Thursday, Galileo makes a minor modification to its radio signal as it approaches a period of unreliable communications. In a few weeks, the orbital motion of Earth and Jupiter will bring the sun between the two, creating radio interference and making reliable communications impossible. Although this geometrical situation, known as superior solar conjunction, is still a few weeks away, the sun's effect on Galileo's radio signal gradually increases in the weeks prior to the main event and then gradually decreases in the weeks after.