Larry Soderblom summarized the satellite data: With respect to the Galilean satellites, “We’re in a relatively high state of ignorance.”
The Io Volcano Watch images seemed to indicate that plume P₂ was now the highest volcano on Io, since P₁ seemed to have become quiet. Io may be the easiest Galilean satellite to try to understand, because we can actually see the geological processes that are shaping the planet. Io’s “twin,” Europa, seems to be where “our highest state of ignorance” lies. “The faint bright streaks which show some relief are evidently different from the diffuse dark bands which don’t seem to show topography, but the similarity of these forms [that both the light and dark markings are of planetary scale] suggests that they must be related.”
Ed Stone speculated about the other two Galilean satellites. Ganymede and Callisto are essentially identical in size, mass, and probably composition. By examining them, we can perhaps learn what happens when bodies with very similar chemistry have different “life histories” and different surface properties (there are indications that Ganymede’s crust may not have been as rigid as Callisto’s). Going further, he added that Callisto and Mercury, the least dense and the most dense, respectively, of the terrestrial-style planets, although totally different in composition and density, seem to have similar surfaces and similar histories. What would have happened to Mercury if it had been made of ice, water, and rock as Callisto is? Would it have evolved as Callisto did?
One of the most spectacular of the Voyager 2 images was obtained from inside the shadow of Jupiter. Looking back toward the planet and the rings with its wide-angle camera, the spacecraft took these photos on July 10 from a distance of 1.5 million kilometers. The ribbon-like nature of the rings is clearly shown. The planet is outlined by sunlight scattered from a haze layer high in the atmosphere. On each side, the arms of the ring curving back toward the spacecraft are cut off by the planet’s shadow as they approach the brightly outlined disk. [P-21774B/W]
The rings of Jupiter proved to be unexpectedly bright when seen with the Sun nearly behind them. Strong forward scattering of sunlight is characteristic of small particles. These two views were obtained by Voyager 2 on July 10 from a perspective inside the shadow of Jupiter. The distance of the spacecraft from the rings was about 1.5 million kilometers. Although the resolution has been degraded by camera motion during the time exposures, these images reveal that the rings have some radial structure. [260-610B/W and 260-674]
HIGHLIGHTS OF THE VOYAGER 2 SCIENTIFIC FINDINGS[3]
Atmosphere