Scientists Say They Can Finally Explain Saturn's Weirdly Shaped Inner Moons
If you thought moons always look ours—white, cratered, and sphere-shaped—Saturn's inner moons prove otherwise: of its roughly 150 moons, the inner ones run the gamut from flying saucer-shaped (like Atlas) to rocky-looking fingers (like Prometheus) to walnuts (like Pan). To Phys.org, some of them resemble ravioli or spaetzle, a type of German noodle, but what's even more fascinating than their weird shapes is how those shapes came to be.
The secret is actually Saturn's shape.
Saturn isn't a rocky planet like Earth—instead, it's made of hydrogen and helium, meaning that it doesn't have a solid surface (though it may have a solid core). Because of this gaseous composition, its rotation causes it to flatten near its poles and bulge outward near its equator, making it an 'oblate spheroid'.
The slightly flattened shape means there's a narrow band around the planet where things gets trapped by Saturn's gravity, including its inner moons. Because the moons are all orbiting in the same narrow area, they have a tendency to crash into each other, usually at shallow angles.
Previous theories hypothesized that Saturn's inner moons might have gradually formed from particles in its rings, but a new study by researchers at the University of Bern claims that their strange shapes came from colliding and merging with one another.
By simulating impacts between moons, members of the organization NCCR PlanetS found that they could account for the shapes of moons like Pan and Prometheus almost to a 'T'—when comparing their models to the photos taken by the Cassini spacecraft, they matched up almost perfectly.
The key, it turns out, was the shallow impact angles: if a moon T-bones another moon at a 90-degree angle, the resulting mashup is unlikely to hold together.
However, head-on collisions and collisions at oblique angles end up creating something more stable, though the shape can range from bulbous to narrow.
Meanwhile, our moon may have done the opposite: something huge crashed into Earth, and our planet apparently spat out the chunk of molten rock that would become the Moon. But that's a more complicated story.