Saturn is one of the most distinctive planets in the solar system thanks to its iconic rings, but surprising new research suggests that those rings weren't always there. In fact, they may have formed during the age of dinosaurs here on Earth.
In other words, Saturn's rings — and many of its moons too — might not just be babies on a galactic timescale. They might be babies on a geological timescale. If a time-traveling scientist went back to the Age of Dinosaurs and peered through a telescope at Saturn, it might have been a far different looking system.
NASA scientists recently analyzed data from the Cassini spacecraft's final missions in 2017. Towards the end of Cassini's mission, the spacecraft performed 22 dives between the planet and its rings to measure mass of the rings. Cassini calculated the mass by feeling the gravitational pull. From that, the scientists were able to study the rings' age.
"Only by getting so close to Saturn in Cassini's final orbits were we able to gather the measurements to make the new discoveries," said Cassini radio science team member and lead study author Luciano Iess, of Sapienza University of Rome. "And with this work, Cassini fulfills a fundamental goal of its mission: not only to determine the mass of the rings, but to use the information to refine models and determine the age of the rings."
The researchers knew that lower mass means a younger age. So from the data, they knew that the rings were likely formed by a comet that was ripped apart by Saturn's gravity or another event that broke apart icy moons because the rings are bright and made of ice. If the rings were similar in age to the planet, they would likely be darker and contaminated from debris.
This new analysis supports previous evidence proving that Saturn's rings are younger than the planet.
Still young at 100 million years old
In 2016, researchers calculated the age of Saturn's rings by studying the orbital tilt of the planet's inner moons. Orbital tilt is what happens to an orbiting body when it gets tugged and yanked by the gravity from other nearby objects, essentially making it more elongated. As an object like a moon becomes elongated, it begins to tilt out of its original orbital plane. By comparing the current orbital tilt of Saturn's inner moons to predictions made through computer simulations about their implied age, scientists calculated that they are probably only around 100 million years old.
"Moons are always changing their orbits. That's inevitable," Matija Cuk, principal investigator at the SETI Institute, told Phys.org. "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."
It's a profound thing to fathom. Up until now, the working assumption about Saturn's rings was that they were primordial, as old as the planet itself. It's humbling to think that such a prominent feature of one of the largest planets in our solar system could be a recent development. The fact that we're able to witness them today is an incredibly lucky moment in the history of the solar system.
Such an event would probably have been spectacular to witness in time lapse — if only we were born about 100 million years earlier to witness it.
Editor's note: This article has been updated since it was originally published in March 2016.