Today on Galileo - November 4, 1997
The observing schedule intensifies today on the third day of the Europa - Orbit 11 encounter period. Instruments on board Galileo turn their attention to Jupiter, Io, Europa and Callisto. The spacecraft reaches a distance of 30 Jupiter Radii (2.1 million kilometers or 1.3 million miles) from Jupiter at about 8 AM Pacific Standard Time (PST) and, about 11:15 PM PST, reaches its closest point to Callisto for this orbit at a distance of 673,000 kilometers (418,000 miles).
First on today's activity schedule, the Ultraviolet Spectrometer (UVS) instrument looks at the southern nightside of Jupiter's atmosphere. This observation is designed to look for auroral activity and provide information on the particles involved in its creation. The UVS instrument then performs another observation of Callisto at a solar phase angle of 61 degrees. The Extreme Ultraviolet spectrometer (EUV) joins the UVS instrument in looking at the Io torus, the donut-shaped cloud of gases along Io's orbit. Some of the material from this torus is believed to come from volcanic eruptions on Io. This observation is one of several that are repeated from orbit to orbit. This one in particular provides information that allows the science community to track changes in the shape and size of the Io torus. This nearly 11 hour observation is interrupted to perform other observations but continues later in the day for another 3 hours.
Among these other observations is one of Io while eclipsed from the sun by Jupiter. This observation is performed by the Solid-State Imaging (SSI) camera and is designed to observe thermal hot spots, volcanic plumes and any other types of emissions. The UVS instrument also steals a glance at Jupiter's brightside. This observation is also one of many repeated from orbit to orbit and provides scientists with a snapshot of the distribution of hydrogen and carbon elements in Jupiter's atmosphere. These "hydrocarbon" distributions can also be tied to the distribution of energy in Jupiter's atmosphere.
After the Io torus observation is finished, the UVS instrument looks at Europa. At this point in its orbit, Europa finds herself in Jupiter's shadow. With this observation the UVS team hopes to provide further evidence of whether Europa has a tenuous atmosphere and what is looks like without sunlight.
Today's closest approach to Callisto is marked by a single observation of Callisto performed by the Photopolarimeter Radiometer (PPR) instrument. In this observation, a dayside thermal map, the instrument will provide a full disk map of the temperatures on the surface of the satellite, at least of the surface that is pointing toward the spacecraft at the time of the observation.