Jeff realized that a small moon must be orbiting within this gap. As each particle at the gap edge passes the moon, it receives a gravitational tug that sets up this pattern. Once Jeff got home, he and his colleague Jeff Scargle set about examining all the other Voyager images of the Encke Gap. By assembling all of that data, they pinned down the moon–for now, let’s just call it “TBD”–into a 30-degree sector of longitude where no high-resolution images were available. They published their work in 1985 under the title, Wavy Edges Suggest Moonlet in Encke’s Gap. This is “discovery” paper #1.

Meanwhile, scientists were examining other ring data from the Voyager flyby. Two instruments had obtained “occultation profiles”–measurements of ring opacity at fine resolution across the rings. Both of the occultations showed periodic bright-dark variations near the Encke Gap, but at different locations and with different wavelengths. Jeff and I realized that these were slices through spiral patterns, which could be understood as another aspect of TBD’s influence on the ring. We called the phenomenon a “moonlet wake”. These patterns provided enough information that we were then able to pin down the precise orbit of still-unseen TBD. We published that paper in 1986, Satellite “wakes” and the orbit of the Encke Gap moonlet. “Discovery” paper #2.

After that, our interest in the topic subsided because it seemed, due to bad luck, that the Voyagers simply had not imaged the moon. (Also, meanwhile, we had the Voyager flybys of Uranus and Neptune to deal with.)

This brings us to June 1990, and one fundamental change. The Voyager images were finally available on that brand new, high-capacity storage medium, the CD-ROM. One morning it dawned on me that I had everything I needed to perform a truly comprehensive search for TBD. I had all 30,000 Voyager images of Saturn at my fingertips. I knew when they were taken and where they were pointed. Also, from paper #2, I knew exactly where TBD ought to be along its orbital path at each image time. I left for work that morning telling my husband that my plans for the day were to discover a moon of Saturn.