New Hypothesis for the Origin of Saturn’s Moons


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Saturn Formation Theory

Asphang and Reufer came up with their theory by performing computer simulations of the formation of Saturn’s system of moons. They postulated various scenarios and calculated the resulting moon system of these scenarios. When a calculated moon system matched Saturn’s actual moon system, they found the scenario that likely formed Saturn’s moon system.

The key is collisions: Asphang and Reufer suggest that Saturn started with a moon system similar to Jupiter’s. Saturn initially had several large moons. These moons were however less massive than Titan or Jupiter’s Galilean moons because Saturn is less massive than Jupiter. The proposed collisions might have occurred either late in the period when Saturn’s moons were forming or after a stable moon system had formed.

A Cassini image of Saturn’s moons, Titan and Enceladus, showing the relative sizes of the two moons. Image Credit: NASA/JPL

Their calculated simulations show that if Saturn’s large moons collided in a giant impact and merger with another similar sized body, the outer layers of the smaller satellite release spiral arms composed of icy materials. The icy spiral arms then coalesce into middle-sized moons with sizes and compositions similar to Saturn’s middle-sized moons. The merged moons stick together to form a single larger moon. After a series of such collisions, Saturn was left with one very massive moon relative to the planet, Titan, and over a half dozen middle-sized moons.

In this context icy materials include both water ice and ices of other common materials that are either liquid or gaseous on Earth.

Colliding Moons?

The idea of colliding moons may sound far-fetched to some – moons and planets are far enough apart that they should not collide. However, the current best theory for Earth’s Moon’s origin, the giant impact model, involves similar collisions between the forming Earth and an object about the size of Mars. In the early solar system there was much more debris and small objects floating around, hence collisions would have been much more frequent.

This theory is not yet perfect, but at this point it is a very plausible explanation for the unusual features of Saturn’s moon system. According to Asphang, new data from NASA’s Cassini mission to Saturn will help test this new hypothesis.


Asphaug, E.,Reufer, A. Final Origin of the Saturn System. (2012). Presented at the American Astronomical Society’s Division for Planetary Sciences.

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