Saturn’s rings aren’t something you find easily – and a new theory suggests they formed when one of the gas giant’s own moons got too close to the massive planet.
This unfortunate companion may have been caught in the intense gravitational field of its host, which then literally tore it apart. Scientists believe that the resulting debris may have formed much of the rings we see today. At least that’s what a team of researchers led by MIT’s Jack Wisdom, who named the lost moon “Chrysalis,” suggests. An outline of team theory can be found in a publication in the latest issue of the journal Science.
Wisdom says this story also helps explain the unusual tilt of Saturn’s axis and why the rings are thought to be just over 100 million years old, when Saturn itself formed more than 4 billion years ago.
“The inclination is too large to result from known formation processes in a protoplanetary disk or from later, large collisions,” Wisdom it said in a statement. “Various explanations have been proposed, but none are entirely convincing. The cool thing is that the previously unexplained young age of the rings is naturally explained in our scenario.”
Finding Saturn’s Lost Moon
Saturn orbits the sun tilted more than 26 degrees to one side, a position even more dramatic than Earth’s tilt, which fluctuates between 22.1 and 24.5 degrees. The most likely explanation for this has long been that Saturn’s tilt comes from a sort of gravitational dance the planet engages in with Neptune.
But Wisdom and his colleagues, aided by data from NASA’s Cassini spacecraft, ran some new models that suggest that while Saturn and Neptune were once in resonance in the past, something changed about 160 million years ago. And that thing basically removed Saturn from Neptune’s influence.
Out of a number of simulations, the one that best fits all the data is a hypothetical case in which Saturn loses a relatively large moon.
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Today, the giant’s planetary system hosts 83 moons; Chrysalis would be roughly the size of Iapetus, which is currently Saturn’s third largest moon. Scientists in the new study theorize that between 200 and 100 million years ago, the forgotten moon began to be pushed away from the gravitational field of Titan, Saturn’s largest moon. In turn, this would disrupt Chrysalis’ orbit, sending it on a chaotic path that included a near-collision with Iapetus and Titan, and ultimately too close to Saturn itself.
Such an encounter, the researchers say, could have torn the moon apart, with much of the debris likely swallowed up by Saturn and a small portion forming what we know today as these magnificent rings. It seems like the perfect explanation, solving two cosmic mysteries at once, but Wisdom cautions that it remains a theory.
“Like any other result, it will have to be looked at by others,” he said, adding that in the meantime it makes for a great story.
“Just like the chrysalis of a butterfly, this satellite was dormant for a long time and suddenly became active and the rings appeared.”