Saturn’s gravitational force shredded an old moon, creating its iconic rings and unusual tilt, new research suggests

• New models suggest Saturn’s gravity shredded a moon, Chrysalis, about 160 million years ago.

• The old moon could explain two longstanding mysteries: Saturn’s iconic rings and its dramatic tilt.
• Researchers believe Chrysalis was probably about the same size as Iapetus, Saturn’s third-largest moon.

Scientists say a single moon could solve two cosmic mysteries about Saturn.

When Galileo Galilei first looked at Saturn in 1610, the astronomer noted that the planet appeared to have “ears.” They turned out to be the iconic rings of Saturn. How and when these rings formed has occupied astronomers ever since.

Another mystery of Saturn is its dramatic 27-degree side tilt. According to researchers, this tilt is too great to have formed during the gas giant or to have been the result of collisions that knocked the planet over. In comparison, the tilt of the earth varies between 22.1 and 24.5 degrees.

In a study published Thursday in the journal Science, researchers ran a series of simulations suggesting that Saturn’s rings and its unusual tilt may have formed 160 million years ago, when one of its icy moons destabilized and entered a chaotic orbit fell around the planet. Eventually, the moon — which researchers dubbed Chrysalis — got too close to the gas giant and was torn apart.

The models are based on data from the final stages of NASA’s Cassini mission, which orbited Saturn and its moons for 13 years before dipping into the planet’s atmosphere in 2017.

Today, the giant’s planetary system is home to 83 moons. Researchers believe Chrysalis was probably about the same size as Iapetus, Saturn’s third-largest moon.

Researchers said about 99% of Chrysalis’ remains fell into Saturn’s atmosphere, while the remaining 1% remained in orbit, leaving behind a debris-strewn ring that formed the planet’s iconic Great Rings.

“Just like a butterfly’s pupa, this satellite was long dormant and suddenly became active, and the rings appeared,” said Jack Wisdom, lead author and professor of planetary sciences at MIT, in a statement.

Planetary scientists have long suspected that Saturn’s tilt may result from gravitational interactions with Neptune. To obtain information about the planet’s tilt, the researchers used simulations to calculate Saturn’s moment of inertia, which relates to how much force was required to tip the planet on its side. They found that while Saturn may have once been gravitationally synchronized with Neptune, something changed about 160 million years ago, removing Saturn from Neptune’s influence.

“Then we started looking for ways to bring Saturn out of Neptune’s resonance,” Wisdom said. Resonance occurs when two celestial bodies keep realigning after a certain number of orbits. They theorized that an old moon, Chrysalis, may have held Saturn under Neptune’s influence until it dissipated, allowing Saturn to hover just out of resonance with Neptune.

Wisdom stressed that more data will be needed to see if the theory holds. “It’s a pretty good story, but like any other finding, it needs to be investigated by others,” Wisdom said. He added that the small moon in the pupa phase appears to have acted like a butterfly, revealing its rings once it was torn apart by Saturn’s gravity.