Giant Impacts Formed The Moons Of Saturn
October 17, 2012

Giant Collisions Formed The Moons Of Saturn

Lee Rannals for — Your Universe Online

Planetary scientists claim in a paper published in Icarus that Saturn's moons may have formed due to giant impacts.

Erik Asphaug, professor of Earth and Planetary Sciences at the University of California, Santa Cruz (UCSC), presented the new model at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society (AAS).

Asphaug and co-author Andreas Reufer of the University of Bern found that Saturn's middle-sized moons were created during giant impacts in which several major satellites merged to form Titan, the planet's largest moon.

The team proposes that the Saturnian system started with a family of major satellites comparable to the four large moons of Jupiter, known as the Galilean moons.

"We think that the giant planets got their satellites kind of like the Sun got its planets, growing like miniature solar systems and ending with a stage of final collisions," Asphaug said in a press release. "In our model for the Saturn system, we propose that Titan grew in a couple of giant impacts, each one combining the masses of the colliding bodies, while shedding a small family of middle-sized moons."

A theory known as the Giant Impact Theory tells a story that the Moon was created through a collision with Earth and another planetary body. Asphaug and Reufer's research shows a similar past for Titan.

They said that just as our Moon is thought to be made out of the material similar to Earth's rocky mantle, Saturn's middle-sized moons are made of a material similar to Titan's icy mantle.

"Our model explains the diversity of these ice-rich moons and the evidence for their very active geology and dynamics," Asphaug said in the release. "It also explains a puzzling fact about Titan, in that a giant impact would give it a high orbital eccentricity."

Using computer simulations, the researchers found that mergers of satellites the size of the Galilean moons can liberate ice-rich spiral arms, mostly from the outer layers of the smaller colliding moons. Gravitational clumping of the spiral arms leads to the formation of clumps with sizes and compositions that resemble Saturn's middle-sized moons.

"These satellite collisions are a regime that is not very well understood, so the modeling opens up new possibilities in general for planet formation," Reufer said in the release.

Asphaug said that what makes the Saturn system so beautiful and unique could be its youth.

"While we don't have a preferred timeframe for this origin scenario to play out, it could have happened recently if something came along to destabilize the Saturn system, triggering the collisional mergers that formed Titan," he said. "This 'something' could have been the close passage of a marauding Uranus and Neptune, which is part of the Nice model."

Asphaug acknowledged a couple of dynamical issues raised by the new model as well. The clumps that came to be from the giant impacts might get swept up into the accretion of Titan, rather than evolving into separate moons with their own orbits.

Also, simulations of the dynamical evolution of the complicated system are needed to further explore and validate the researchers' model.

Asphaug said that new data from NASA's Cassini mission on the geophysics of Saturn's moons will provide the best tests for the model.

"Our model makes strong predictions for how Titan was assembled, what the middle-sized moons are made of, and how they started out as rapidly spinning clumps of ice-rich material," he said in the release. "So it's testable. These little moons could provide the clues telling us what happened, and when."