Illustration by Maren Slobody

Saturn’s rings get most of the attention, but the real action happens with its moons.

Erik Asphaug, a UC Santa Cruz earth and planetary sciences professor, along with Andreas Reufer of the University of Bern presented a hypothesis that explains mysterious irregularities in Saturn’s satellite system. This took place on Oct. 19 in Reno, Nev. at the annual meeting of the Division for Planetary Sciences.

Asphaug and Reufer hypothesize that Saturn had a different set of satellites prior to its current formation, and that its current system of moons is relatively recent. In addition, the scientists have theorized that Saturn’s former moons merged to form Titan, and the material thrown into space as a result of these collisions then formed Saturn’s mid-sized moons.

“[The mid-sized moons] are really strange,” Asphaug said. “They’re about 1 percent the mass of Titan. The moon is … 1 percent the mass of the earth.”

The presence of mid-sized moons around Saturn is particularly irregular because of a massive cosmic upheaval that occurred roughly 4.1 billion years ago, known as Late Heavy Bombardment (LHB), Asphaug said.

“Some catastrophic event scattered large impactors throughout the solar system, causing a ‘spike’ in the number of impacts half a billion years after the solar system formed,” said Francis Nimmo, a UCSC professor of earth and planetary sciences. “Because many of these impactors were large — tens or hundreds of miles across — and traveling very fast, they were enormously destructive.”

Saturn’s mid-sized moons are so small that it is highly unlikely they would have survived this chaotic period in the life of the solar system, Nimmo said.

“The standard picture of the late heavy bombardment would have almost certainly destroyed the innermost moons, and reduced the others to lumpy rock-rich remnants,” Nimmo said.

This discrepancy led Asphaug and Reufer to form their hypothesis that Saturn’s current satellite system is relatively recent.

The frequent collisions that occurred during LHB may have thrown Saturn’s former moons out of orbit, Asphaug said. This caused collisions between the moons, and caused them to accrete, or merge.

“Titan just formed by larger and larger mergers,” Asphaug said.

To recreate possible collision scenarios, Asphaug and Reufer used virtual simulations that show Saturn’s moons’ formation.

“The physical processes behind such giant collisions are too complex to be studied analytically,” Reufer said. “The general idea is therefore to solve the mathematical equations representing the involved physical processes like gravity and thermodynamics on a computer.”

These collision scenarios are simulated by assigning physical properties to virtual particles, Reufer said. In other words, virtual particles are programmed to act like physical bodies, like two colliding moons.

“The remnants in our simulation therefore do not represent exactly the remnants of the collision that really occurred,” Reufer said. “But our simulation shows that such a collision is able to deliver remnants in the order of magnitude in mass, that is required to explain the [mid-sized moons].”

Earth’s sole satellite, the moon, formed in a process similar to that of Saturn’s moons, Asphaug said. According to the Lunar Cataclysm Theory, a massive vessel collided with the Earth billions of years ago. The impact was at such a large scale that a considerable portion of Earth’s mantle was thrown into space and set into orbit around planet Earth.

Hypothesizing about the collisions that formed our moon and Saturn’s mid-sized moons, which Reufer describes as “little-studied,” may lead to future scientific advances in the field of planetary science.

“We [are] therefore highlighting a process which might be key in planet formation,” Reufer said, “especially for the formation of habitable planets and moons.”


Erik Asphaug’s and Andreas Reufer’s hypothesis will be formally published in Icarus, the official publication of American Astronomical Society’s Division for Planetary Sciences, on a date that has yet to be determined.