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Long lost moon may explain Saturn’s tilt and young rings

Researchers say the moon drifted too close to Saturn, knocking the planet off its axis before breaking apart into ice and debris that orbit the planet in a ring shape.

(CN) — For decades, astronomers have been baffled by Saturn. How did it get those rings, among the most iconic sights in our solar system, which appear to be just 100 million years old — a veritable infancy, given that the planet itself is around 4.5 billion years old?

And why is Titan, Saturn's largest moon and the second largest satellite in our solar system, drifting away from its planet at such an alarming speed, roughly 11 centimeters per year (for comparison, our moon is drifting away from us at less than 4 centimeters per year)?

A new theory offers up a potential solution to these two mysteries, and may also help explain Saturn's distinct tilt. In a paper published Thursday in Science, Jack Wisdom, a professor of planetary science at the Massachusetts Institute of Technology, and his co-authors posit a long lost moon of Saturn's, which they name "Chrysalis."

Chrysalis, they suggest, was about the size of Saturn's third-largest satellite Iapetus. Its orbit became destabilized, so the theory goes, and it came closer and closer to the gas giant. Eventually, about 150 million years ago, Chrysalis was ripped apart by Saturn's tidal forces. Some of its pieces crashed into Saturn, nudging its axis, while other parts of it became the famously sparkling rings of Saturn anyone with an amateur telescope can see today.

"A close encounter of Chrysalis with Saturn would have caused Chrysalis to break apart," Wisdom and his co-authors write. "If we assume that Chrysalis was predominantly made of water ice, like Iapetus, then this debris could have developed into Saturn’s rings." They go on to write: "The required timing of the loss of Chrysalis coincides with the estimated age of the rings.

Wisdom and his colleagues developed their theory by studying data collected from the Cassini mission, which sent an unmanned spacecraft flying by Venus, Earth, an asteroid named "2685 Masursky," Jupiter, and then, finally, Saturn, where it burned up in 2017. The mission revolutionized our understanding of Saturn and its many moons, and the data it collected is still being analyzed and interpreted. Wisdom and his co-authors used data collected by the Cassini probe to create numerical simulations that explain "the obliquity of Saturn, the young age of its rings, and the eccentricity of Titan."

"It explains several things that were previously thought to be not related," Wisdom said in a phone interview. "Some anomalies in the orbit of Titan. The age of the rings. The'yre all explained by this."

He added: "Right now, it’s a pretty nice package."

Wisdom, 69, is a pioneer in the study of chaos as it applies to the universe. Though some may picture our solar system as something like a finely tuned mechanical watch, its planets and satellites all orbiting in some perfect balance, Wisdom's research paints a far more disorderly picture.

"The whole planetary system evolves chaotically," said Wisdom. "Chaos has a lot to do with planetary problems.

"It makes it harder to predict the future."

Follow @hillelaron
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