The violent death of the moon Chrysalis may have produced Saturn’s rings

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WASHINGTON – Call it the case of the missing moon.

Scientists using data from NASA’s Cassini spacecraft and computer simulations said Thursday that the destruction of a large moon that got too close to Saturn was responsible for both the birth of the gas giant planet’s magnificent rings and its unusual orbital inclination of about 27 degrees would be responsible.

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The researchers dubbed this hypothetical moon Chrysalis and said it may have been torn apart by tidal forces from Saturn’s gravitational pull about 160 million years ago – relatively recent compared to the date of the planet’s formation, more than 4.5 billion years ago.

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About 99% of the Chrysalis wreckage appears to have crashed into Saturn’s atmosphere, while the remaining 1% remained in orbit around the planet, eventually forming the great ring system that is one of the wonders of our solar system, the researchers said. They chose the name Chrysalis for the moon because it refers to the pupal stage of a butterfly before transforming into its magnificent adult form.

“Like a butterfly emerging from a chrysalis, Saturn’s rings emerged from the primal satellite Chrysalis,” said Jack Wisdom, professor of planetary science at the Massachusetts Institute of Technology and lead author of the study, published in the journal Science http://www.science.org /doi/10.1126/science.abn1234.

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Researchers estimated that Chrysalis was about the same size as Iapetus, Saturn’s third-largest moon at just over 900 miles (1,470 km) in diameter.

“We assume that it consisted mainly of water ice,” said planetary scientist and study co-author Burkhard Militzer of the University of California, Berkeley.

Consisting mostly of water ice particles ranging in size from a grain of sand to the size of a mountain, Saturn’s rings extend as far as 170,000 miles (282,000 km) from the planet but are generally only about 10 meters thick. While the Solar System’s other major gaseous planets, including Jupiter, also have rings, they pale in comparison to those of Saturn, the sixth planet from the Sun.

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Saturn is almost 10 times as far from the Sun as Earth and is the second largest planet in our solar system after Jupiter, with a volume 750 times larger than Earth. Made mostly of hydrogen and helium, Saturn is orbited by 83 known moons, including Titan, the solar system’s second largest moon – larger than the planet Mercury.

Orbiting Saturn 294 times from 2004 to 2017, Cassini obtained key data, including gravitational measurements, crucial to the new study before the robotic explorer made a fatal dive into the planet.

A study published in 2019 provided evidence that the rings were a relatively recent addition, and the new research extends those findings. In the new study, the researchers proposed a multi-step process to explain the formation of Saturn’s rings.

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The Saturn system formed with Chrysalis among the many moons present, they said. Initially, the planet’s axis of rotation was perpendicular to its plane of orbit around the Sun, but the gravitational effects of distant planet Neptune on the Saturn system tilted Saturn’s axis of rotation.

The drama began when Titan’s orbit around Saturn began to drift outward – a process that is still happening – and destabilized Chrysalis’ orbit, they said. Titan’s outward migration is thought to be relatively rapid at about 11 cm per year — which doesn’t sound like much, but over time it means a lot, especially for such a large moon.

Chrysalis’ orbit deteriorated and the moon ventured so close to Saturn that it disintegrated, the researchers said.

“Saturn’s gravitational pull ripped it apart the way Jupiter ripped comet Shoemaker-Levy 9 apart,” Militzer said, referring to a comet that eventually crashed into Jupiter in 1994.

“With Chrysalis gone, Neptune could no longer change Saturn’s axis of rotation. So the planet rotated at an angle of 27 degrees,” Militzer added.

In comparison, the tilt of the earth is about 23 degrees.

(Reporting by Will Dunham, Editing by Rosalba O’Brien)