Pan: Saturn’s Ravioli-Shaped Moon

The universe served up a piece of Astro-pareidolia last week when humanity got its first close-up look at Saturn's tiny moon Pan. Appropriately named after the half-man, half-goat satyr from Greek mythology, Pan is nestled in the Encke (pronounced EN-key) Gap within Saturn's A ring. NASA's Cassini spacecraft flew just 15,268 miles past the moonlet (closer than the distance to the geosynchronous satellites from Earth) on March 7th.

Cassini's close-up of Saturn's moon Pan -  NASA / JPL-Caltech / Space Science Institute.

'Nearing its end, Cassini delights again,” says Carolyn Porco (Space Science Institute) on Twitter. “Here is 35-km Pan in mind-blowing detail with its unmistakable accretionary equatorial bulge.”

Mark Showalter (then at Stanford University) discovered Pan on July 16, 1990. Showalter and colleagues first inferred the tiny moon's presence by the waves it kicked up in the wake of its passage through the Encke Gap. After accurately predicting the moon's orbit, Pan was found in 11 images taken by Voyager 2 during its August 1981 flyby.

The moon orbits Saturn every 13.8 hours from an average distance of 134,000 kilometers (80,150 miles), equivalent to about one-third the Earth-Moon distance, and just 73,000 miles from the Saturnian cloud tops), the 34x31x21-kilometer moon carves out the Encke Gap in Saturn's outermost bright A Ring. On Earth, Pan would just barely fit inside Tampa Bay. The moon has an albedo (or reflectance) of 50%, equivalent to dirty snow.

Unlike the narrow 35-kilometer-wide Keeler gap occupied by the tiny moonlet Daphnis, the wider 325-kilometer Encke Gap also hosts a tenuous ringlet that Pan braids and modifies. While the Daphnis is slightly inclined to the plane of Saturn's rings by 0.0036 degrees and kicks up vertical waves in its wake, the orbit of Pan is nearly flat with an inclination of only 0.0001 degrees, and it induces spiral density waves in the ring plane.

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