Saturn’s rings are arguably the most beautiful feature of our entire Solar System. Far from just capturing the attention of millions of ordinary people around the world, astronomers have also been puzzling over them ever since they were discovered in 1656. Centuries later, scientists are still unsure as to how or when they actually formed.
A new study, due to be published in the Astrophysical Journal, reveals that these icy rings may be younger than previously thought. Instead of appearing at the dawn of the Solar System, they may have appeared at the twilight of the age of the dinosaurs.
The research team, led by Matija Cuk, an astronomer at the Search for Extraterrestrial Intelligence (SETI) Institute in California, used the orbits of the gas giant’s many moons and rings in order to work out where they might have been millions of years ago.
“Moons are always changing their orbits. That's inevitable,” said Cuk in a statement. “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.”
Tethys, one of the icy inner moons of Saturn, pictured center. NASA/JPL-Caltech/Space Science Institute
The space around Saturn is pretty crowded. Earth only has our one Moon, but this gargantuan ringed beast has upward of 62. Some of them are more like small planets, particularly the rocky, muddy Titan; many of them, however, are icy spheres, like Enceladus, which has not only a global ocean beneath its surface, but cryovolcanoes.
In order to have both a liquid ocean and icy volcanoes, Enceladus needs to be generating heat from within. It does this through a mechanism called tidal heating, wherein its celestial dance with Saturn – amplified by the orbits of the many other moons – exerts a powerful gravitational pull on the inner segments of the planet. This causes frictional heating at depth, which induces melting.
The researchers think that Enceladus’ tidal heating has always been powerful, meaning that the tidal forces in the Saturnian system have always been strong. Something was amiss, though: Strong tidal forces would have caused the orbits of the various icy moons, like Tethys, Dione and Rhea, to long ago be dramatically altered. This means that, if these frigid satellites were billions of years old, their orbits shouldn’t look like they do today.
The icy geysers or “cryovolcanoes” on Enceladus. NASA
This strongly suggests that the icy moons themselves are actually quite young. Having formed recently, they simply haven’t been experiencing the powerful tidal forces for a very long time at all, so their orbital paths haven’t yet been significantly altered. The team ran computer simulations to confirm their theory, and found that these icy, inner moons are only about 100 million years old – which means they were born when several of the Tyrannosaurs roamed the Earth.
But what of the rings? Well once upon a time, there were more of these icy moons. “Eventually, the orbits of neighboring moons crossed, and these objects collided,” Cuk added. “From this rubble, the present set of moons and rings formed.”
This celestial tale of death and rebirth means that we’re lucky enough to be around to see them today.