Saturn’s Rings Could Be Formed by a Missing Moon that Smashed into Planet 160 Million years ago.

Saturn’s Rings Could Be Formed by a Missing Moon that Smashed into Planet 160 Million years ago – According to a new study, Saturn’s tilt and rings could be due to an ancient missing moon. A “grazing encounter” might have broken the moon into pieces to create Saturn’s rings.

The rings of Saturn, which are seen swirling around Saturn’s equator, indicate that the planet is tilted. The belted giant spins at a 26.7-degree angle relative to the plane it orbits the sun. Astronomers suspect that the tilt is due to gravitational interactions between Neptune and Saturn. Saturn’s tilt moves at a similar rate to Neptune’s orbit.

A new study by astronomers at MIT has shown that while Neptune and Saturn may once have been in sync, Saturn is now free from Neptune’s influence. This planetary realignment was caused by what? One hypothesis was tested by the team: A missing moon.

Saturn's Rings Could Be Formed by a Missing Moon that Smashed into Planet 160 Million years ago.

The team suggests that Saturn, home to 83 moons and several satellites today, had at least one additional satellite, which they call Chrysalis. This is according to a Science study. Researchers suggest that Chrysalis orbited Saturn with its siblings for several billions of years, pulling and tugging at the planet in a manner that kept its tilt or “obliquity” in resonance with Neptune.

The team estimates that Chrysalis was unstable 160 million years ago and got too close to Neptune in a grazing encounter, which caused the satellite to fall apart. Saturn could free itself from Neptune’s grip by stealing the moon, leaving it with the current-day tilt.

Researchers speculate that while most of Chrysalis’ shattered body may not have struck Saturn, some fragments could have remained in orbit and eventually broken into smaller icy pieces to form the planet’s signature rings.

The missing satellite could solve two long-standing mysteries: Saturn’s current tilt and the age of its rings. These rings were previously thought to be around 100 million years old, much older than the planet.

Jack Wisdom, professor of planetary science at MIT, is the new study’s lead author.

Rola Dbouk at MIT and Burkhard Militzer of the University of California at Berkeley were co-authors. William Hubbard at the University of Arizona was also involved. Francis Nimmo, Brynna Downey and Francis Nimmo are all from the University of California at Santa Cruz. Richard French of Wellesley College is also a co-author.

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Moment of progress

Scientists proposed in the 2000s that Saturn’s tilted orbit was due to Neptune being in resonance or gravitational relationship with Saturn. NASA’s Cassini spacecraft observed Saturn from 2004 to 2017. This added a new dimension to the problem. Scientists discovered that Titan, Saturn’s largest satellite, was moving away from Saturn faster than expected. It moved at an average of 11 centimetres per year. Scientists concluded that Titan’s rapid migration and gravitational pull led to Titan being pulled away from Saturn faster than expected.

This explanation is based on a central mystery: Saturn’s moment inertia. It is the distribution of mass in the planet’s inner. Saturn’s tilt may behave differently depending on whether Saturn’s core is closer to the surface or farther away.

Wisdom states, “To move forward on the problem, we had to determine when Saturn’s inertia is at its peak.”

The missing element

Wisdom and his coworkers sought to determine Saturn’s moment inertia by using Cassini’s last observations. This was the phase during which Cassini made a very close approach to map the gravitational fields around the planet. You can use the gravitational field to determine the distribution and mass of the planet.

Wisdom and his coworkers modelled Saturn’s interior and found a mass distribution that corresponded to the gravitational field Cassini observed. Surprisingly, the newly identified moment inertia put Saturn within, but not outside, Neptune’s resonance. Although the planets were once in sync, they are now not.

Wisdom says, “Then we went on a hunt for ways to get Saturn out of Neptune’s resonance.”

First, the team performed simulations to simulate Saturn’s orbital dynamics and its moons. This was to determine if any natural instabilities between the satellites could have affected the planet’s tilt. The search was unsuccessful.

Researchers reexamined mathematical equations that describe the precession of a planet, which describes how the planet’s axis changes over time. This equation includes contributions from all satellites. The team argued that removing one satellite from this equation could impact the planet’s precession.

It was a question of how large the satellite would need to be and what dynamics it would need to experience to remove Saturn from Neptune’s resonance.

Wisdom and his coworkers ran simulations to determine the satellite’s properties, including its mass, orbital radius, and the orbital dynamics required to knock Saturn out.

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They concluded that Saturn’s current tilt is due to Neptune’s resonance and that Saturn’s loss of Chrysalis (a satellite about the size of Iapetus, Saturn’s third-largest, allowed it to escape the resonance.

Chrysalis was in orbital chaos around 200 to 100 million years ago. He had a few close encounters with Titan and Iapetus but eventually got too close to Saturn. A grazing encounter saw the satellite ripped to pieces, leaving only a tiny portion to circle the planet as debris-strewn rings.

They found that Saturn’s precession and tilt today, along with the late formation of its rings, is explained by its loss of Chrysalis.

Wisdom states, “It’s a fairly good story, but as with any result, it will need to be evaluated by others,” in an article reprinted with permission from MIT News. It seems this satellite loss was just a chrysalis waiting for its instability.

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