Discovered by Galileo 400 years ago, Saturn's rings are the most remarkable thing astronomers with small telescopes can find in our solar system.

But even today, experts have not been able to come to an opinion on how or when they formed.

According to a new study published Thursday in the prestigious journal Science, 100-200 million years ago, an icy moon named Chrysalis came close to the gas giant and exploded there.

Some of the dust from the explosion was absorbed by Saturn and the rest of the fragments broke up into ice layers and formed the planet's signature rings.

"It's nice to find a plausible explanation," Jack Wisdom, professor of planetary sciences at MIT and lead author of the new study, told.

Saturn, the sixth planet from the Sun, was formed four and a half billion years ago, at the beginning of the solar system.

But a few decades ago, scientists suggested that Saturn's rings appeared much later: only about 100 million years ago.

The hypothesis was reinforced by observations made by the Cassini probe, which orbited Saturn from 2004 to 2017.

"But because no one could think of a way to make the rings 100 million years ago, some people have been questioning the reasoning that led to that deduction," said Wisdom.

By constructing complex mathematical models, Wisdom and colleagues found an explanation that both justified the timeline, and allowed them to better understand another characteristic of the planet, its tilt.

In the new study, Wisdom and colleagues modelled the planet's interior using gravitational data gathered by Cassini during its close approach

"Grand Finale," its last act before plunging into Saturn's depths.

The model they generated found Saturn is now slightly out of sync with Neptune, which necessitated a new explanation — an event powerful enough to cause the drastic disruption.

Working through the mathematics, they found a lost moon fit the bill.

"It's pulled apart into a bunch of pieces and those pieces subsequently get pulled apart even more, and gradually roll into the rings."

The missing Moon was baptized Chrysalis by MIT's Wisdom, likening the emergence of Saturn's rings to a butterfly emerging from a cocoon.

The team thinks Chrysalis was a bit smaller than our own Moon, and about the size of another Saturn satellite, Iapetus, which is made entirely of water ice.

"So it's plausible to hypothesize that Chrysalis is also made of water ice, and that's what it needs to make the rings because the rings are almost pure water.

Asked whether he felt the mystery of Saturn's rings stood solved, Wisdom replied, soberly, "We've made a good contribution."

The Saturn satellite system still holds "a variety of mysteries," he added.