Pan: a small “ravioli moon” of Saturn

March 11, 2017 • 10:15 am

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:

(NASA / JPL-Caltech / Space Science Institute)
(NASA / JPL-Caltech / Space Science Institute)

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:


Two views of Atlas, Saturn’s moon (NASA)

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.

23 thoughts on “Pan: a small “ravioli moon” of Saturn

  1. Atlas looks like a won ton as prepared by some restaurants here in NYC. I’m celebrating noodle day by having some won ton noodle soup.

  2. It wonderful to have such close images of this and the other moons. It makes the connection to our planetary neighborhood so much more complete. As we discover more, I imagine some of the old sci-fi books will now be outdated. On the other hand if an author years ago described a moon of Saturn as ravioli shaped… wouldn’t that be a win!

    1. As we discover more, I imagine some of the old sci-fi books will now be outdated.

      Occupational hazard.
      One author wrote a story about “the coldest place” (in the solar system), as the “dark side” of Mercury. Between the story being written and published (IIRC in a “pulp mag,” but I won’t hang for that), some inconvenient astronomer discovered that Mercury isn’t tidally locked, and so all it’s surface gets a gentle broiling every couple of months.

  3. what about our moon? what are we chopped liver? Jupiter’s Ganymede is the second largest moon in the solar system after our Moon.

    1. No, Ganymede is the largest moon in the solar system; our Moon is fifth (after Titan, Callisto and Ion). Ganymede and Titan are also bigger than Mercury.

      1. The moon is biggest if you relative size compared to the Planet, not in absolute terms. If you are doing astronomical orbit calcs, you have to take the centre of the earth-moon system (barycentre). You can ignore it for Mercury-Neptune.

  4. Maybe this is the Pastafarians’ equivalent the the Vatican. Maybe they are wrong about the Invisible Flying Spaghetti Monster. The Tortellini G-d anyone?

  5. It will actually be 20 years after launch — 13 (actually more like 14) years after arriving in Saturn orbit.

  6. I haven’t been following this closely, but I did comment somewhere that it looks like the “equatorial ridge” on Iapetus. Which is also about 5km high. I hadn’t previously seen this structure described as “equatorial”, but if confirmed it would make it at least the second structure in it’s class, if not more.

  7. scientists didn’t want to contaminate any of Saturn’s moons in case they prove habitable.

    Habitability is mostly a given in the case of Enceladus (global ocean with an alkaline pH comfortably within the habitable range of our own extremophiles). And Titan has interesting chemistry too that one would like to preserve pristine (albeit its inner ocean is likely too alkaline). The primary effort is to avoid threatening an existing biosphere.

    The middle ground of having contaminated a habitable but dead world is somewhat more lenient. Already having contaminated a pristine world we should be able to identify the source from genomics, given a later sample.

    1. HTML fail, let me try again:

      scientists didn’t want to contaminate any of Saturn’s moons in case they prove habitable.

  8. Surely we can think of some sort of bread that it looks like, to fit the name. (“Pan” meaning “bread” in some Latin-derived languages, and in Japanese via Portuguese missionaries.)

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