Just before closest approach, at 6:35 p.m., the ultraviolet instrument watched as a bright star passed behind Ganymede and reemerged ten minutes later. No dimming that could be attributed to an atmosphere was seen; when the data were analyzed later, scientists set an upper limit for any gas on this satellite at one-billionth of the atmospheric pressure at the surface of the Earth. As encounter day drew to a close, celebrations took place all over JPL. For many, however, the excitement was tempered by exhaustion. After 48 hours of intense activity, sleep was imperative for some. But the close approach to Callisto was still to come, as was an examination of the data already received. [Illustration: After its close flyby of Io, Voyager 1 headed for Ganymede, the largest of the Galilean satellites. This global view of Ganymede, taken on March 4 at a range of 2.6 million kilometers, shows features as small as 50 kilometers across. At the time, Voyager scientists speculated that the numerous white spots were impact craters, surrounded in some cases by icy ejecta blankets splashed onto the surrounding surface. However, many narrow white streaks, especially those in the lower left quadrant, promised new and exciting geological features on this satellite. [P-21207C]] Tuesday, March 6. Voyager was now receding from Jupiter, accelerated on a new trajectory—one that would speed it on toward its November 1980 encounter with Saturn. But first came the encounter with Callisto, with closest approach at 9:50 a.m., at a range of 126 000 kilometers. The satellite was littered with craters and there appeared one huge “bullseye” pattern that might have been the result of an impact. As the photos of Callisto came in, Garry Hunt described the scene in the imaging area: “The activity around the monitors now is quite incredible with people caught breathless by the pictures coming in. Every satellite we’ve seen has been a different world.” Asked how he felt about the images of Jupiter’s atmosphere, he replied, “I’m absolutely delighted with what I’ve seen, and I’m delighted Voyager 2 is not far behind since I’m convinced that we’ll see yet another face of Jupiter by then. The weather will have changed by July.” At the morning press briefing, the wealth of new data began to be revealed. “If Jupiter had ever posed for Monet, it would probably have turned out like this,” said Brad Smith as he introduced some enhanced (exaggerated) color images that had been specially processed to show more detail in the Great Red Spot region. Indeed, these photographs did look like paintings with Jupiter displaying some of its best abstract art.