March 10, 2017

Cassini images show strange shape of Saturn’s moon Pan

The jury appears to be out as to whether Pan looks more like a ravioli, a walnut, a flying saucer, President Donald Trump’s face or something else entirely, but new images of Saturn’s tiny moon obtained by NASA’s Cassini spacecraft make it easy decide for yourself.

The little moonlet, which according to The Verge is about 20 miles wide and resembles “a little space rock with what looks like two googly eyes,” resides in what is known as the Encke Gap, a 200-mile-wide space between Saturn’s rings that is caused by the diminutive object itself.

In the new images, captured by Cassini as the probe nears the end of its ten-plus year mission, Pan can clearly be seen to be a rounded rock with a ring around its equator, which has naturally caused it to be compared to various objects (including ravioli, walnuts and pierogies).

The second innermost moon of Saturn, Pan is what is known as a ring shepherd, meaning that it keeps the Encke Gap free of ring particles. Due to its gravitational influence, the moon picks up particles and deflects them from their original orbits through orbital resonance, causing the gaps in the ring system by effectively herding the particles as if they were sheep.

In a statement, NASA said that the new, unprocessed images were taken by Cassini on Tuesday from a distance of 15,268 miles (24,572 kilometers). “These... are the closest images ever taken of Pan and will help to characterize its shape and geology,” the US space agency added.

So how did the moon get its unusual rocky ring?

While NASA has yet to clean-up the photographs, Mashable noted that the unusual rocky ridge surrounding the moon (which is officially known as an accretionary equatorial bulge) can still be clearly seen. It was apparently formed by the odd gravitational interplay surrounding Pan.

In fact, the website cites a 2007 study which suggested that the formation of the bulge was due to the accumulation of particles that had fallen from Saturn’s rings onto the moon’s surface. In fact, Pan isn’t the only moon of Saturn’s to have such a ridge – Cassini had previously spotted one on Atlas, the moon closest to the sharp outer edge of the planet’s A ring.

While its existence was first predicted in 1985, Pan was not officially discovered until five years later, when Mark Showalter and his colleagues spotted what was then the 18th moon of Saturn in images taken by Voyager 2 nearly a decade earlier. In an interview with National Geographic,  Showalter said that it was “very gratifying finally to see Pan’s closeup” and that the new images were “a far cry from the nondescript ‘dots’ that I was tracking way back in 1990!”

“The shape, as others have also pointed out, is probably because it is always sweeping up fine dust from the rings,” said Showalter, who now works with the SETI Institute in California. “The rings are very thin compared to the size of Pan, so the dust accumulates around its equator.”


Image credit: NASA/JPL-Caltech/Space Science Institute