There was also a yearning to examine more closely, with the Galileo Project, what had been unknown for so long, yet had become so familiar in only a few months’ time—the little dark, red “potato” Amalthea, the volcano-covered world Io, the mysterious “cracked billiard ball” Europa, cratered and groovy Ganymede, ancient Callisto, and the king of the planets itself, a colorful, banded world of stable climate and ever-changing weather patterns. [Illustration: A fifteenth satellite of Jupiter was discovered in the spring of 1980 by Steven Synnott of JPL. It was first seen on this Voyager 1 image taken March 5, 1979, in which the 75-kilometer-diameter satellite shows as a dark oval against the planet. Also visible is the shadow of the satellite, designated 1979J2. This satellite orbits between Io and Amalthea with a period of 16 hours and 11 minutes. [P-22580B/W]] [Illustration: The Jupiter seen by the Voyager cameras is a cloud-belted world of rapid jet streams and complex cloud forms. Prominent in this Voyager 1 image, taken February 5 at a range of 28.4 million kilometers, is the alternating structure of light zones and dark belts, and the Great Red Spot and numerous smaller spots. Also easily visible are the two inner Galilean satellites, Io and Europa. The resolution in this picture is 500 kilometers, about five times better than can be obtained from Earth-based telescopes. Callisto can be faintly seen at the lower left. [P-21083C]] CHAPTER 8 JUPITER—KING OF THE PLANETS A Star That Failed More massive than all the other planets combined, Jupiter dominates the planetary system. The giant revealed by Voyager is a gas planet of great complexity; its atmosphere is in constant motion, driven by heat escaping from a glowing interior as well as by sunlight absorbed from above. Energetic atomic particles stream around it, caught in a magnetic field that reaches out nearly 10 million kilometers into the surrounding space, embracing the seven inner satellites. From its deep interior through its seething clouds out to its pulsating magnetosphere, Jupiter is a place where forces of incredible energy contend. At its birth, Jupiter shone like a star. The energy released by infalling material from the solar nebula heated its interior, and the larger it grew the hotter it became. Theorists calculate that when the nebular material was finally exhausted, Jupiter had a diameter more than ten times its present one, a central temperature of about 50 000 K, and a luminosity about one percent as great as that of the Sun today.