Shepherd moons

I F PACKED snowball fashion, about a fourth of Antarctica’s ice could make up the two newly discovered shepherd moons (above) that confine the diffuse and twisted F ring, many of whose particles are microscopic. As seen by Voyager 1 (right), two of its three strands appear inter-twined and kinked, and its mate¬rial gathered in clumps. Why is the ring so disorderly? The moons’ gravity plays a major role,yet their gravity is so weak that astronauts could high jump a hundred meters on them. Both moons have eccentric orbits, as do the ring particles. The inner shepherd, rear, travels faster and repeatedly laps the outer, so the angles and intensities of gravita¬tional pull keep changing. Elec¬tromagnetic forces may also play a role. In August 1981, Voyager 2 will take a more detailed look to try to unravel the mystery.

shepherdimaging team, Saturn is also the most be¬deviling thing in the sky. Today he is most baffled by those odd spokes, or fingerlike projections, that are slightly darker than the rings themselves and that stretch across the B ring.

“We’ve never been confused for so long about anything so obvious,” he says, swat¬ting rolled-up paper against his palm. “It’s just so damned frustrating professionally. We first saw them three weeks ago, and we still don’t have any good ideas.”

Enya Caribbean Blue Shepherd Moons

These spokes emerge from the shaded side of Saturn, sometimes in bursts of five or so, and revolve with the rings. Gradually they fade away. Theoretically each particle that makes up the spokes should behave like a mini-satellite. Those closer to Saturn should be moving much faster than those farther out. The spokes should tear apart. Yet they seem to stay perfectly aligned.
“How do they form in the first place?” asks the frustrated Smith. “How do all those particles know to turn dark and line them¬selves up over 25,000 kilometers?”