Fried Egg? Flying Saucer? Nope. Just Cool New Closeups of Saturn’s Moon Pan

This new view of Saturn’s moon Pan is the closest yet, snapped by Cassini from a distance of 15,268 miles (24,572 km) on March 7, 2017. Pan measures 22 miles wide by 14 miles across and displays a number of small craters along with parallel ridges and grooves. Its broad, thinner equatorial ridge displays fine, parallel striations. Credit: NASA/JPL/Space Science Institute

Besides Earth, Saturn may be the only other planet where you can order rings with a side of ravioli. Closeup photos taken by the Cassini probe of the the planet’s second-innermost moon, Pan, on March 7 reveal remarkable new details that have us grasping at food analogies in a feeble attempt to describe its unique appearance.

A side view of Pan better shows its thin and wavy ridge likely built up through the accumulation of particles grabbed from Saturn’s rings. The ridge is between 0.9 and 2.5 miles (1-4 km) thick. Credit: NASA/JPL/Space Science Institute


As Pan moves along the Encke Gap its gravity creates ripples in Saturn’s A-ring. Credit:
NASA/JPL/Space Science Institute

The two-part structure of the moon is immediately obvious: a core body with a thin, wavy ridge encircling its equator. How does such a bizarre object form in the first place? There’s good reason to believe that Pan was once part of a larger satellite that broke up near Saturn long ago. Much of the material flattened out to form Saturn’s rings while large shards like Pan and another ravioli lookalike, Atlas, orbited within or near the rings, sweeping up ring particles about their middles. Tellingly, the ridges are about as thick as the vertical distances each satellite travels in its orbit about the planet.

Pan casts its shadow on Saturn’s A-ring from within the 200-mile-wide (325 km) Encke Gap, which is maintained by the presence of the moon. Pan shares the gap with several diffuse ringlets from which it may still be gathering additional material around its equatorial ridge. Credit: NASA/JPL/Space Science Institute

Today, Pan orbits within and clears the narrow Encke Gap in Saturn’s outer A-ring of debris. It also helps create and shape the narrow ringlets that appear in the gap It’s lookalike cousin Atlas orbits just outside the A-ring.

Pan and Altas (25×22 miles) orbit within Saturn’s ring plane and may both be fragments from a larger moon breakup that created Saturn’s rings. Both have swept up material from the rings to form equatorial ridges. Credit: NASA/JPL/Space Science Institute

Moons embedded in rings can have profound effects on that material from clearing gaps to creating new temporary ringlets and raising vertical waves of material that rise above and below the ring plane. All these effects are produced by gravity, which gives even small objects like Pan dominion over surprisingly vast regions.

Enjoy this animated gif created from photos of the close flyby of Pan. Credit:
NASA/JPL/Space Science Institute


Bob King

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.

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