At about 5 a.m. on March 8, Voyager had taken a historic picture. Looking back at a crescent Io from a distance of 4.5 million kilometers, the camera had been used to obtain a long-exposure view for the spacecraft navigation team—one that showed the satellite against the field of background stars. During the day, Linda Morabito, an optical navigation engineer, began to work with this picture on her computer-controlled image display. She noted what appeared to be a crescent cloud, extending beyond the edge of Io. But Io has no atmosphere, so a cloud rising hundreds of kilometers above the surface did not seem to make sense. The next day, working with her colleagues, Morabito eliminated all possibilities for the new feature on Io except the obvious—a cloud. If it were a cloud, it must be the result of an ongoing volcanic eruption of incredible violence. The picture was shown to members of the Imaging Team, who agreed with the identification. But it was Friday and Brad Smith and Larry Soderblom, along with most of the other team members, had left for the weekend to try to get some rest. The picture would have to wait two more days. HIGHLIGHTS OF THE VOYAGER 1 SCIENTIFIC FINDINGS[2] Atmosphere Uniform wind speeds for cloud features with widely different size scales, suggesting that mass motion and not wave motion is being observed. Rapid formation and spreading of bright cloud material, perhaps the result of disturbances that trigger convective activity. A pattern of east-west winds in the polar regions, previously thought to have been dominated by convective upwelling and downwelling. Anticyclonic motion of material associated with the Great Red Spot, with a rotational period of about six days. Interactions of smaller spots with the Great Red Spot and with each other. Auroral emissions in the polar regions, both in the ultraviolet (which were not present during the 1973 Pioneer encounter) and in the visible. Cloud-top lightning bolts, similar to terrestrial superbolts, and meteoritic fireballs. A temperature inversion layer in the stratosphere and a temperature of 160 K at the level at which the atmospheric pressure is 0.01 bar. Very strong ultraviolet emission from the disk, indicating a thermospheric temperature of more than 1000 K. A hot (1100 K) upper ionosphere on the dayside that was not observed by Pioneer 10, suggesting there may be large temporal or spatial changes. An atmospheric composition with volume fraction of helium of 0.11 ± 0.03. A substantially colder atmosphere above the Great Red Spot than in the surrounding regions. Satellites and Rings At least eight currently active volcanoes on Io, probably the result of tidal heating of the interior of the satellite, with plumes extending up to 250 kilometers above the surface. A large hot spot on Io near the volcano Loki that is about 150 K warmer than the surrounding surface.