In a 15-second exposure with the wide-angle camera, the edge-on ring shows as a faint line, and the satellite is the dot indicated by the arrow. [260-807]
In a narrow angle 96-second exposure, the motion of the satellite can be seen. Again, the faint band is the ring, blurred by camera motion, and the arrow indicates the streak due to the satellite. A star streak is located above and to the left of the satellite; note that the length and angle of the two trails are different, owing to satellite motion. [P-22172]
A New Satellite
One of the most fascinating discoveries of Voyager 2 was not recognized at first. Graduate student David Jewitt of the California Institute of Technology, working with Imaging Team member Ed Danielson, began a detailed analysis of all the ring photos in late summer. In early October he determined that a short streak on a photo taken July 8, previously presumed to be an image of a star trailed by the time exposure, did not correspond to any known star position. Perhaps this was a new satellite! Additional sleuthing turned up a second image of the same part of the ring that also showed the anomalous object, together with trails due to known stars. The differing angles and lengths of the trails of the object and the stars confirmed that this was indeed a 14th satellite of Jupiter. Following the guidelines of the International Astronomical Union, it was designated 1979J1, pending later assignment of a mythological name. The proposed name is Adrastea, a nymph who nursed the infant Zeus in Greek legend.
The newly discovered satellite orbits Jupiter at a distance of 58 000 kilometers above the equatorial cloud tops, placing it just at the outer edge of the ring and much closer to the planet than is Amalthea, previously thought to be the innermost satellite. It travels at 30 kilometers per second (nearly 70 000 miles per hour), circling Jupiter in just seven hours and eight minutes. From its brightness, scientists guessed that it might be 30-40 kilometers in diameter.
The proximity of Adrastea to the ring suggests a relationship between the two. When the discovery was announced to the press in mid-October, it was speculated that the ring material might originate on the satellite, perhaps eroded away by the energetic charged particles in the inner Jovian magnetosphere. Once again, Voyager had added to our perspective on planetary processes, suggesting that undiscovered but similar small satellites might also be associated with the rings of Saturn and Uranus.
Voyager 2 had certainly added a few years’ of data of its own to Voyager 1’s “ten years’ worth of data.” It had given a different view of the Jovian system, helping to solve some of the mystery surrounding Jupiter and its satellites, and creating new mysteries. As Voyager 2 sped out away from Jupiter, riding along the giant planet’s huge magnetotail, attention turned to Saturn: What would Pioneer 11, the Pathfinder, discover in September 1979? What would the Voyagers learn in November 1980 and August 1981? Would all go well? Would Voyager 2 fly on to Uranus?
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.