Five years have passed since the arrival of high-resolution Cassini Mission images of Saturn’s bizarre moon Iapetus that the international planetary community has pondered the unique walnut shape of the large (735 kilometer radius) body, considered by many to be one of the most astonishing features in the solar system.
William B. McKinnon, PhD and Andrew Dombard, PhD propose that at one time Iapetus itself had a satellite, or moon, created by a giant impact with another big body. The sub-satellite’s orbit, they say, would have decayed because of tidal interactions with Iapetus, and it would have gradually migrated towards Iapetus. At some point, the researchers say, the tidal forces would have torn the sub-satellite apart, forming a ring of debris around Iapetus that would eventually slam into the moon near its equator, reports USA Today and The Tucson Citizen.
“Imagine all of these particles coming down horizontally across the equatorial surface at about 400 meters per second, the speed of a rifle bullet, one after the other, like frozen baseballs,” says McKinnon. “Particles would impact one by one, over and over again on the equatorial line. At first the debris would have made holes to form a groove that eventually filled up.”
“When you have a debris ring around a body, the collisional interactions steal energy out of the orbit,” explains Dombard. “And the lowest energy state that a body can be in is right over the rotational bulge of a planetary body — the equator. That’s why the rings of Jupiter, Saturn, Uranus and Neptune are over the equator.”
“We have a lot of corroborating calculations that demonstrate that this is a plausible idea,” says Dombard, “but we don’t yet have any rigorous simulations to show the process in action. Hopefully, that’s next.” [PRESS RELEASE]