I like my eggs over easy but would never have guessed I could order up a moon that way. I mean look at it. Nature offers up possibilities no human could ever dream of. Pan is Saturn’s second-innermost moon and orbits inside the planet’s outer A-ring. Its gravity has cleared a lane in that ring called the Encke Gap that has all to do with Pan’s peculiar shape as we’ll learn in a moment. NASA’s orbiting Cassini probe took these new photos — the closest ever — on March 7 from a distance of just 15,268 miles (24,572 km).
So how did Pan come to wear such a big, wide belt that compels us to compare it to fried eggs, ravioli, biscuits, pasties, pot pies and flying saucers? To find an answer, we have to go back into the distant past when astronomers surmise a larger moon broke up near the planet either by through a collision with another moon or crumbled by Saturn’s overwhelming gravity.
The mashup would have shattered the former moon into many pieces which spread out to form Saturn’s rings. Pan would have survived as one of the larger fragments orbiting within the rings.
Though small compared to our moon, Pan’s gravity would have swept up ring particles as it orbited Saturn. Since the rings are only about 30 feet or 10 meters thick in most places (though parts of the main rings can be about 2 miles thick), Pan accumulated ring stuff only around its belly or equator in the shape of a thin, wavy ridge. It’s a delicious consequence that the formation of Saturn’s rings may have spurred the growth of another sort of ring around one its moons.
The “flap” is between 0.9 and 2.5 miles (1-4 km) thick which just happens to be the vertical distance the satellite travels as it orbits about the planet. As for those parallel groovy grooves that line the ridge, I wonder if they might have formed from ring material “rolling down the hill” so to speak and leaving tracks. At the base of the striations, there appear to be debris piles similar to talus at the base of a hill or mountain.
Let’s hope mission control will direct Cassini to take an even closer look at this bizarre little moon one more time before the mission ends this September.