Astronomers have long known that Pan, one of the “shepherd moons” in Saturn’s rings, had a weird shape. But it took this week’s high-resolution images from the Cassini orbiter to show them just how weird.

Cassini got its closest look ever at Pan on Tuesday, when it came within a little more than 15,000 miles of the 20-mile-wide moon. In the close-ups released on Thursday, the thing looks like a flattened flying saucer, complete with a bulging ridge around the edge.

Overnight, the views sparked rounds of hilarity and awe on Twitter. Was it a cosmic turtle shell? Walnut? Ravioli? And what’s behind that strange, strange shape?

Homing in on one strange-looking moon in an alien system far, far away. All in a day's work for our wandering observer at 10 AU from the Sun pic.twitter.com/UgVAcj4Vgr — Carolyn Porco (@carolynporco) March 9, 2017

That’s it…I’m not fat, I have an accretionary equatorial bulge. ? https://t.co/f9shsUMk0a — Angela Taylor (@PartPurple) March 9, 2017

We’re in for some major suffering when this thing hatches. https://t.co/G0oCsBjTii — Paul Czege (@PaulCzege) March 9, 2017

Close-up of the celestial ravioli orbiting around Saturn. No news on whether it’s filled with cheese or spinach. Still, it’s awesome. https://t.co/jrB5lQwQAd — Nancy McGuire (@WordChem) March 9, 2017

After 13 yrs, we've come to expect extreme reactions to our images. But hunger? Ravioli, tortellini, empanada, pierogi, hamburger, brie? — Carolyn Porco (@carolynporco) March 9, 2017

And here is 18-mile-wide Pan in its native environment, living in a gap in Saturn’s rings. https://t.co/Q5N1nEyr2x pic.twitter.com/6BnRNW8mS9 — Corey S. Powell (@coreyspowell) March 10, 2017

Carolyn Porco, who leads the imaging team for the soon-to-be-concluded Cassini mission, pointed to a couple of papers published nearly a decade ago that explain why Pan (named after the pipe-playing shepherd god of Greek mythology) looks the way it does.

Like Saturn’s other shepherd moons, Pan plies its way between sections of the giant planet’s rings, clearing out a gap as it goes. In Pan’s case, that’s the Encke Gap of the A ring.

Pan’s gravitational field pulls in icy particles from the edge of the ring as it makes its rounds. That’s how it helps keep the rings in shape, by “shepherding” stray ring particles. Some of that fine-grained material piles up around the saucer moon’s middle to create a smooth, protruding ridge.

For what it’s worth, Pan is by no means the only weirdo in the Saturnian system. There’s Iapetus, a two-toned moon that has its own walnut-type ridge; Hyperion, a moon that looks like a giant sponge; and Mimas, the “Death Star” moon.

More planetary wonders from this week: