New models suggest that Saturn’s gravity destroyed a moon, Chrysalis, about 160 million years ago.
The ancient moon could explain two long-standing mysteries: Saturn’s iconic rings and dramatic tilt.
Researchers think that Chrysalis was probably the size of Iapetus, Saturn’s third largest moon.
Scientists say a single moon could clarify two cosmic mysteries about Saturn.
When Galileo Galilei first observed Saturn in 1610, the astronomer noticed that the planet had what appeared to be “ears”. They turned out to be the iconic rings of Saturn. How and when these rings formed have puzzled astronomers ever since.
Another mystery of Saturn is its dramatic 27 degree tilt to one side. According to the researchers, that tilt is too large to have formed when the gas giant did or to have been the result of collisions that brought the planet down. In comparison, the tilt of the Earth fluctuates between 22.1 and 24.5 degrees.
In a study published Thursday in the journal Science, researchers ran a series of simulations that suggest that Saturn’s rings and its unusual inclination may have formed 160 million years ago when one of its frozen moons destabilized and fell into a chaotic orbit around the planet. Eventually the moon, which the researchers dubbed Chrysalis, got too close to the gas giant and was torn apart.
The models are based on data from the final phase of NASA’s Cassini mission, which spent 13 years in orbit around Saturn and its moons before plunging into the planet’s atmosphere in 2017.
Today the giant’s planetary system is home to 83 moons. Researchers think that Chrysalis was probably the size of Iapetus, Saturn’s third largest moon.
The researchers said about 99% of Chrysalis remains immersed in Saturn’s atmosphere, while the remaining 1% remained in orbit, leaving in its wake a debris-strewn ring that formed the planet’s iconic great rings.
“Just like a butterfly’s chrysalis, this satellite has long been dormant and suddenly become active, and the rings have emerged,” Jack Wisdom, lead author and professor of planetary science at MIT, said in a statement.
Planetary scientists have long suspected that Saturn’s tilt may result from gravitational interactions with Neptune. To gather information about the planet’s tilt, the researchers used simulations to calculate Saturn’s moment of inertia, which refers to how much force was needed to tilt the planet to one side. They found that while Saturn may have been gravitationally synchronized with Neptune, something changed about 160 million years ago, which removed Saturn from Neptune’s influence.
“Then we went looking for ways to take Saturn out of the Neptune resonance,” Wisdom said. Resonance occurs when two celestial bodies continue to realign after a certain number of orbits. They theorized that an ancient moon, Chrysalis, could have kept Saturn under Neptune’s influence until it disintegrated, allowing Saturn to move just out of resonance with Neptune.
Wisdom pointed out that more data will be needed to see if the theory holds up. “It’s a pretty good story, but like any other result, it will have to be reviewed by others,” Wisdom said. He added that the small moon appears to have acted like a butterfly in the chrysalis phase, with its rings emerging once it has been pierced by Saturn’s gravity.
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