On September 15, the Cassini spacecraft, 13 years after launch and after helping scientists acquire tons of knowledge, will cease its orbiting of Saturn and plunge into the planet’s atmosphere, disintegrating in the process. This suicidal move was deliberate, as scientists didn’t want to contaminate any of Saturn’s moons in case they prove habitable. Just four days ago, though, it took some amazing pictures of one of Saturn’s moon’s, Pan.
Wikipedia says this about Pan:
Pan. . . is the second-innermost moon of Saturn. It is a small, walnut-shaped moon approximately 35 kilometres across and 23 km wide that orbits within the Encke Gap in Saturn’s A Ring. Pan is a ring shepherd and is responsible for keeping the Encke Gap free of ring particles.
It was discovered by Mark R. Showalter in 1990 from analysis of old Voyager 2 probe photos and received the provisional designation S/1981 S 13 because the discovery images dated back to 1981.
But Pan is one of only many moons of Saturn:
Saturn has 62 moons with confirmed orbits, 53 of which have names and only 13 of which have diameters larger than 50 kilometers, as well as dense rings with complex orbital motions of their own.
Seven Saturnian moons are large enough to be ellipsoidal in shape, though only two of those, Titan and Rhea, are currently in hydrostatic equilibrium. Particularly notable among Saturn’s moons are Titan, the second-largest moon (after Jupiter’s Ganymede) in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape including hydrocarbon lakes and dry river networks; and Enceladus, which is seemingly similar in chemical makeup to comets, emits jets of gas and dust and may harbor liquid water under its south pole region.
And Pan’s shape, well, as an Atlantic article said, “This moon orbiting Saturn looks a lot like ravioli“. Indeed it does:
It’s unusual for a moon to be so oddly shaped, but The Atlantic explains:
Pan gets its pasta-like shape from smooth bulges protruding on all sides from its center, known as equatorial ridges. The ridges lie in the same plane as Saturn’s rings. In 2007, researchers suggested that the ridge could be made up of particles from Saturn’s rings that got stuck on Pan when it was just an average moonlet. The same process may have occurred on Atlas, another moon, which orbits beyond the edge of Saturn’s A ring, one of the planet’s thickest bands of rings. Atlas has a distinct smooth ridge, too:
Pan resides in a lane of its own making within the A ring. The moon maintains a 200-mile break in the ring, known as the Encke Gap, perpetually pushing on nearby ring particles and preventing them from filling in the space. It creates waves in the ring material as it goes, leading some of it to bunch up in certain spots. Pan is named for the Greek god of the wild and shepherds, a fitting moniker for a moon whose job is to keep the rings on either side of it in line.
Here’s a flyby gif showing Pan, and another gif closer up.
For more on some really lovely pictures of Saturn’s rings taken by recently by Cassini, see this post by Jason Davis at The Planetary Society.