(_Range to Jupiter, 3.5 million kilometers_). With the first satellite encounter still two days away, Voyager 2 continued to make a variety of measurements of Jupiter and all the Galilean satellites. As the distance to Io decreased, it was possible to see detailed surface features as well as to look for the volcanic plumes at the edge of the disk, silhouetted against black space. By the end of the day, the Great Red Spot loomed so large that six imaging frames (a 2 × 3 mosaic) were required to encompass it and its immediate surroundings. At the first formal press conference of the Voyager 2 encounter, Project Scientist Ed Stone reviewed the progress of the mission. Because the ailing spacecraft receiver was working so well, Ray Heacock, Voyager Project Manager, announced that the major trajectory correction maneuver at Jupiter had been rescheduled to take place only two hours after closest approach. Since the geometry was especially favorable at this time, the 76-minute rocket burn could put the spacecraft on its planned route to Saturn with a minimum expenditure of fuel, thereby preserving the option of sending the spacecraft on to Uranus. The Io torus was under observation, both directly by the ultraviolet spectrometer, and indirectly by the charged particle instruments. The LECP instrument had begun to pick up sulfur ions, but at lower energies and lower concentrations than those recorded during the first encounter. In the ultraviolet, glows could be seen both from the torus and from aurorae in the polar regions of Jupiter. Photographs of Io showed that the heart-shaped feature surrounding Pele (P₁), Io’s largest volcano, had changed shape. The indentation of the heart had disappeared, making the heart into an oval. Apparently a new deposit of volcanic ejecta had blanketed the surface, altering its color. Perhaps an earlier obstruction in the volcanic vent, or the shape of the vent itself, had caused the area surrounding Pele to look heart-shaped. In any case, whatever had caused the indentation was now gone. At the same time, new photos failed to show a plume above Pele, and there was speculation that changes in this eruption might be related to the altered population of charged particles in the magnetosphere. [Illustration: The Voyager 2 pictures of Callisto looked remarkably similar to those obtained of the other side of the satellite by Voyager 1. Seen from a distance of 2.3 million kilometers, the large craters (100 kilometers or more across) appear as light spots. No new major impact features such as Valhalla, discovered by Voyager 1, are visible on the hemisphere seen by Voyager 2. [P-21740C]] Saturday, July 7.