Jupiter (Planet) -- Photographs from space; Jupiter probes; Voyager Project
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?
Public-domain text, read in full here on John Shaqi.
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