Real Reason Why Saturn Is the Only Planet With Huge Rings in Our Solar System

Could Saturn's mysterious lost moon be responsible for its fascinating rings?
saturn rings

Only three months ago, scientists published reasons why they believed Jupiter doesn’t have a massive ring system like Saturn. They concluded that most of its rings are made of ice, which may have come from comets, which are also mostly made of ice. 

Wikipedia says that Saturn’s rings are the most prominent rings of any planet in our Solar System. They are made up of many tiny particles that range in size from micrometers to meters and circle Saturn. The pieces of the ring are mostly water ice, with just a little bit of rock debris. But there was no agreement on how they were put together. Jupiter didn’t have a visible ring because most of the comet debris was pulled in by Jupiter’s moon.

In new research released this September, scientists have come up with an answer as to why Saturn has a particolored ring system. Its colorful ring system is much bigger than the thin rings of dust and rock surrounding Jupiter, Uranus, Neptune, and even Haumea, a dwarf planet in the Kuiper Belt. 

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Particolored ring system by NASA

The team now has what they say is a plausible answer to why Saturn’s colorful ring system is the way it is.

Chrysalis is a hypothetical Saturn moon proposed by scientists at the Massachusetts Institute of Technology. They did this by using data from the Cassini–Huygens mission. 

The Cassini–Huygens mission was a joint project of NASA, the European Space Agency, and the Italian Space Agency to send a spacecraft to study the planet Saturn and its moon, Titan.

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The origin of Saturn’s rings

The researchers think the moon would have been torn apart by Saturn’s tides about 100 million years ago. This is how its rings were made. 

It would have swallowed up to 99% of the moon’s mass (about the same size as the outer moon Iapetus). The remaining 1% would have been caught in its rings.

How a moon could cause the discs to form, the axis to tilt, and the orbit of Titan to expand

If Saturn’s rings are made of a moon that was crushed, that could explain not only how it got its new dusty discs but also why its axis is tilted and why the orbit of its biggest moon, Titan, is strange and expanding quickly.

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Every planet in the Solar System has an axial tilt, which is the angle between the planet’s spinning axis and its orbital plane. Saturn is tilted at a rate of 26.7 degrees, which is the same as Earth, Mars, and Neptune. 

But its tilt is getting worse, which scientists think is because Titan is moving away from it.

The tilting of Saturn’s ringed world

Researchers have found that gravitational interactions between Saturn, Titan, and Neptune have significantly affected the ringed world’s tilt. The rate at which Saturn’s rotational axis wobbles (called “rotational precession”) is very close to the rate at which Neptune’s entire orbit wobbles (called “orbital precession”). This is called “resonance,” and it suggests that there is a connection between the two.

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SatMoons by NASA

This earlier research found that, contrary to earlier studies, these gravitational stepping-stones would have come together fairly recently. This is because Titan is moving away from the gas giant too quickly for them to have formed in the early Solar System.

The new research, which was done by a group led by MIT astronomer Jack Wisdom, did find something strange, though. They used gravitational data from NASA’s Cassini spacecraft and a planet’s interior structure model to find out if Saturn is still in resonance with Neptune. 

If Titan’s orbit had moved outward as expected but changed unexpectedly, that could have pulled Saturn into resonance with Neptune and then pushed it back out of resonance with Neptune.

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The next step for the researchers was to figure out what could have caused Titan’s orbit to change so much. 

At the moment, Saturn is the planet that has the most known moons in the Solar System. There are 82 of them, and some of them haven’t been confirmed yet. If it had an extra satellite that became unstable, it could have changed the planet’s precession and helped it get out of resonance with Neptune.

The team ran hundreds of simulations of the Saturn system, which included this made-up moon called Chrysalis. Each simulation began in a slightly different way. And they found that this scenario explained everything, from the tilt of the planet’s axis to Titan’s orbit to Saturn’s baby rings.

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In particular, the scenario says that Chrysalis could have caused Saturn to tilt more than it does now, which is about 36 degrees, through resonance with Neptune. During this time, it would have been affected by Titan’s gravity.

The collision of a moon with its planet

Then, about 160 million years ago, Chrysalis’s orbit became less stable. This made it move too close to Saturn, and its gravity pulled it apart.

It’s important to keep in mind that only 17 of the 390 simulations that the team ran led to the conditions that led to the scenarios of how its rings being formed. Does this mean they could be wrong?

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The fate of the Chrysalis

Based on their simulations, the scientists think that about 99 percent of Chrysalis crashed into Saturn, but enough of it stayed in orbit to form the planet’s rings.

If the moon was icy, like other moons in the Solar System, this could explain why there is so much ice in its rings today.

This violent collision could have also thrown Saturn out of resonance, which would have made its axial tilt less steep. 

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The disruption of Chrysalis

In a commentary on the new study, Cornell University astronomer Maryame El Moutamid says that the disruption of Chrysalis is possible and likely. Still, it’s expected to have been a rare, one-time event. It’s not likely that something like this will happen again soon.

The researchers in this paper propose that Saturn once had another satellite orbiting it called Chrysalis. They think the system was previously in a spin-orbit precession resonance with Neptune. This means that as Titan moved, Saturn’s obliquity (the tilt of its axis) increased. The researchers think Saturn escaped the precession resonance because Chrysalis’s orbit was unstable. They think that a close encounter with Chrysalis caused Saturn and its rings to be how they appear today.

According to Wisdom, the theory is a pretty good story and explains things about Saturn that have been hard to understand up until now. However, like any theory, it will need to be looked at by other people. 

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The future of ringed systems

Future research into Saturn’s system and other ringed systems could help figure out how often things like the destruction of Chrysalis are likely to happen. Which other planets can expect a violent Moonfall scenario? Changes in orbits can have massive effects not just on neighboring planets, but also on other planets millions of miles away in the solar system, just as scientists have recently tried to prove that changing Jupiter’s orbit would change the climate on Earth.