According to a new research, some of Saturn’s moons as well as rings came into existence not too long ago. Analysis of specially-developed computer models has revealed that these celestial bodies might have been born a mere hundred million years ago, making them younger than many of the dinosaurs that roamed the Earth in ancient times. Speaking about the discovery, Matija Cuk of the SETI Institute said:
Moons are always changing their orbits. That’s inevitable,” says Matija Cuk, principal investigator at the SETI Institute. “But that fact allows us to use computer simulations to tease out the history of Saturn’s inner moons. Doing so, we find that they were most likely born during the most recent two percent of the planet’s history.
First observed back in the 1600s, Saturn’s rings were until now believed to be as old as the planet itself, which was actually formed over four billion years ago. It was only in 2012 that scientists began to question this belief. At the time, a team of French astronomers found that specific tidal effects – basically gravitational interaction between Saturn’s inner moons and the fluids present deep inside the planet’s interior – are in fact causing the former to alter their orbital radii rapidly.
As the researchers point out, such occurrences can be explained if the moon and the rings are recent phenomena. To arrive at that conclusion, Cuk, along with David Nesvorny and Luke Dones of the Southwest Research Institute, relied on computer modeling to determine the past behavior of the distant planet’s icy inner moons. Unlike our moon that revolves round the Earth along it own orbit, Saturn’s several satellites have to co-exist in the same space.
Due to tidal effects, all of their orbits are growing slowly, but at different speeds. As a result, there are times when two moons enter orbital resonances. According to the scientists, this takes place when one of the moons’ orbital period is a simple fraction, such as one-half or two-thirds, of the other’s orbital duration. When that happens, even moons with relatively weak gravity can significantly alter each other’s orbits, often causing them to elongate and tilt out of their original rotational plane.
To find out how the orbits of Saturn’s satellites grew over time, the team made a comparative study of the moons’ current orbital tilts and the ones predicted with the help of computer simulations. Their research has revealed that the orbits of some of the most well-known satellites, including Dione, Tethys and Rhea, have undergone less change than previously thought. As the researchers point out, their somewhat small rotational tilts actually indicate that these celestial bodies have not yet crossed many of the so-called orbital resonances.
This information, the group believes, suggests that Saturn’s moons came into existence not too long ago. To determine their age, Cuk and his colleagues referred to the data collected by NASA’s Cassini spacecraft while observing ice geysers on the surface of one of the satellites, named Enceladus. Given that these geysers are powered by energy generated as a result of tidal interactions, and that Enceladus has a more or less constant level of geothermal activity, it would be correct to think that the tides within the planet itself are quite strong.
According to the simulations, such small orbital tilts could be brought about in less than 100 million years. If that is indeed true, some of Saturn’s most important moons, excepting Titan and the distant Iapetus, are concurrent with the Cretaceous period on Earth. Cuk added:
So the question arises, what caused the recent birth of the inner moons. Our best guess is that Saturn had a similar collection of moons before, but their orbits were disturbed by a special kind of orbital resonance involving Saturn’s motion around the Sun. Eventually, the orbits of neighboring moons crossed, and these objects collided. From this rubble, the present set of moons and rings formed.
The findings of the research were recently published in the Astrophysical journal.
Source: SETI Institute