Short answers, pulled from the story.
Astronomers Peter Goldreich and Scott Tremaine proposed the theory in early 1979. Their proposal explained how unseen objects could hold planetary ring material in place through gravitational influence.
Voyager 1 confirmed the existence of shepherd moons when it arrived at Saturn later that year. Images from the spacecraft revealed Prometheus orbiting near the F ring to confirm the theory.
Pan maintains the Encke Gap by deflecting particles away from its path while Daphnis carves out the Keeler Gap. These moons create gaps or confine narrow ringlets through their proximity and gravitational forces.
Galatea provides the gravitational influence needed to maintain dense clusters within Neptune's incomplete arcs. Other undiscovered shepherd moons may contribute to the clumpiness observed today alongside this satellite.
The major gap exists approximately 61 million kilometers from the center of brown dwarf J1407b. This feature serves as indirect evidence for an exomoon or exoplanet capable of up to 0.8 Earth masses.