Violent death of moon Chrysalis may have spawned Saturn’s rings
A view of Saturn from NASA’s Hubble Space Telescope captures details of its ring system and atmospheric detail June 20, 2019. Scientists said on Thursday that the destruction of a large moon that moved too close to Saturn would both explain the birth of the gas giant planet. gorgeous rings. (NASA/ESA, A. Simon, MH Wong and the OPAL team via REUTERS)
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WASHINGTON — Call it the missing moon case.
Scientists using data obtained by NASA’s Cassini spacecraft and computer simulations said Thursday that the destruction of a large moon that strayed too close to Saturn would explain both the birth of the planet’s magnificent rings gas giant and its unusual orbital inclination of about 27 degrees.
The researchers named this hypothetical moon Chrysalis and said it may have been torn apart by the tidal forces of Saturn’s gravitational pull perhaps 160 million years ago – relatively recent compared to the date of formation of the planet more than 4.5 billion years ago.
About 99% of the Chrysalis wreckage appears to have sunk into Saturn’s atmosphere while the remaining 1% remained in orbit around the planet and eventually formed 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 it matures into its glorious adult form.
“Like a butterfly emerges from a chrysalis, the rings of Saturn emerged from the primordial satellite Chrysalis,” said Jack Wisdom, professor of planetary sciences at the Massachusetts Institute of Technology and lead author of the study published in the Science magazine.
The researchers estimated that Chrysalis was about the size of Iapetus, Saturn’s third largest moon which is just over 910 miles in diameter.
“We assume it was mostly water ice,” said planetary scientist and study co-author Burkhard Militzer of the University of California, Berkeley.
Saturn’s rings, mostly made of water ice particles ranging from smaller than a grain of sand to the size of a mountain, extend up to 175,000 miles from the planet but are usually only about 30 feet thick. While the other large gaseous planets in the solar system, including Jupiter, also have rings, they pale in comparison to those of Saturn, the sixth planet from the sun.
Located nearly 10 times farther from the sun than Earth, Saturn is the second largest planet in our solar system behind Jupiter, with a volume 750 times that of Earth. Saturn, composed mostly of hydrogen and helium, orbits 83 known moons, including Titan, the second largest moon in the solar system – larger than the planet Mercury.
Cassini made 294 orbits around Saturn from 2004 to 2017, obtaining vital data, including gravity measurements that were key to the new study, before the robotic explorer took a fatal plunge into the planet.
A study published in 2019 provided evidence that the rings were a relatively recent addition, and the new research has expanded those findings. In the new study, the researchers proposed a multi-step process to explain the formation of Saturn’s rings.
The Saturnian system formed with Chrysalis among the many moons present, they said. Initially, the planet’s axis of rotation was perpendicular to its orbital plane around the sun, but the gravitational effects of distant planet Neptune on the Saturnian system tilted Saturn’s axis of rotation.
The drama began when Titan’s orbit around Saturn began to drift outward — a process still ongoing — destabilizing Chrysalis’ orbit, they said. Titan’s outward migration is thought to be relatively rapid, at around 4 inches per year – which doesn’t sound like a lot, but over time it’s 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 tore it apart the same way Jupiter tore Comet Shoemaker-Levy 9 apart,” Militzer said, referring to a comet that finally crashed into Jupiter in 1994.
“With Chrysalis gone, Neptune could no longer change Saturn’s axis of rotation, so the planet was left to spin at an angle of 27 degrees,” Militzer added.
By comparison, Earth’s tilt is about 23 degrees.