It’s not often a spacecraft nabs six moons around another planet in one photo, but there they are – Enceladus (313 miles across), oblong Janus (111 miles), Atlas (19 miles), Pan (17 miles), Daphnis (5 miles) and Epimetheus (70 miles) – nestled in and around Saturn’s rings. We see the unlit southern side of the rings in this picture, which was taken at a distance of 1.7 million miles. The spacecraftÂ was closest to Epimetheus (ep-ee-MEE-thee-us) at the time.
Notice that both Pan and Daphnis are located inside dark gaps within the rings; these are zones where the gravitational interactions between the moons and the ring planeÂ haveÂ cleared away most of the icy ring particles. They’re but two examples of how small moons, acting alone or in consort with other moons, have sculpted many of the planet’s rings. Although Saturn has 53 named moons, astronomers think there are dozens if not hundreds more tiny ones embedded in the ring plane too small to be resolved with Cassini’s camera.
Small moons aren’t massive enough to crunch themselves into spheres through pressures created by their own self-gravity. The borderline between being spherical or irregular in shape is around 300-360 miles for a rocky body and somewhat smaller for icy objects.
Two of Saturn’s more curious moons shown in the first photo are Pan and Atlas, both of which are shaped like flying saucers. Scientists think that each started out as a fragment from an originally larger moon that was shattered by a long-ago collision with a comet or meteoroid. Over time, the remnants attracted icy material from the rings which accumulated along their equators to form a 360-degree shelf or ridge of ice. This scenario neatly explains the fact that the icy extensions lie exactly in the ring plane.
Learn more about Pan and AtlasÂ in this short video with a distinctly French accent
The process of these little moons gathering material around their equators is remarkably similar to what weÂ believe happened during the birth of the solar system over 4.5 billion years ago. The Earth and planets, which lie in a fairly flat plane around the sun, are thought to have formed when bits of rocky and icy materials in a disk surrounding the early sun (analogous to Saturn’s rings) collided, stuck together and grew into the worlds we know today. Was Earth once a smaller, saucer-shaped body that eventually fattened up enough to absorb its ridges? Planets and moons wouldn’t be the only bodies siphoning dust and ice from their surroundings. Newborn stars are also cocooned inside disks of dust and gas from which they draw fresh material in a manner similar to Saturn’s Pan and Atlas. Studying these moons and how they interact with the rings may teach us lessons that apply to phenomena visible across the broader universe.