[Nov. 7, 2023: Staff Writer, The Brighter Side of News]
The belted giant rotates at a 26.7-degree angle relative to the plane in which it orbits the sun. (CREDIT: Creative Commons)
Saturn, the sixth planet from the sun, is distinguished not only by its majestic rings but also its peculiar tilt. The iconic rings encircling the gas giant have long served as a testament to Saturn's 26.7-degree angle of rotation in relation to its orbit around the sun. For many years, astronomers attributed this curious tilt to Saturn's gravitational dance with its celestial neighbor, Neptune.
However, recent research challenges this longstanding belief, unveiling the potential of a missing moon as the chief influencer of Saturn's current obliquity.
Escaping Neptune's Hold
Historically, the belief among astronomers was that Saturn and Neptune were engaged in a gravitational resonance. This meant that as Saturn's tilt wobbled – similar to a spinning top – the pace closely matched Neptune’s orbital rhythm. However, groundbreaking modeling undertaken by a team of astronomers from MIT and other reputed institutions has presented a revolutionary theory that disputes this alignment between the two planets.
Their discovery? A previously unrecognized moon they've christened "Chrysalis."
"From Synchronized Dance to a Game of Tug-of-War"
According to the findings, published in the acclaimed journal Science, Chrysalis might have revolved around Saturn alongside its 83 recognized moons for billions of years. This moon's gravitational influence upon Saturn could have been instrumental in maintaining the planet's tilt in resonance with Neptune.
Approximately 160 million years ago, however, Chrysalis's trajectory shifted. The satellite became unstable, leading to a near-miss with Saturn that resulted in the moon's fragmentation. This catastrophic event is believed to have disengaged Saturn from Neptune's gravitational influence, leading to its unique tilt observable today.
This graphic shows the ring moons inspected by NASA's Cassini spacecraft in super-close flybys. The rings and moons depicted are not to scale. (Credit: NASA-JPL/Caltech)
Furthermore, the debris from Chrysalis's disintegration could have contributed to Saturn's magnificent rings. "Just like a butterfly’s chrysalis, this satellite was long dormant and suddenly became active, and the rings emerged," remarks Jack Wisdom, professor of planetary sciences at MIT and the study's primary author.
The intriguing revelation surrounding Chrysalis offers an explanation for two significant enigmas in the realm of astronomy: the genesis of Saturn's current tilt and the age of its rings, previously estimated at a mere 100 million years – considerably younger than Saturn itself.
Saturn’s normalized angular momentum as a function of rotation period. The red curve and circles represent results for models using physical equations of state with differential rotation (DR), matched to the even gravitational moments up to J12. (CREDIT: Science)
Unraveling the Saturnian Enigma
The quest to demystify Saturn's tilt gained momentum in the early 2000s when scientists hypothesized a gravitational association with Neptune as the underlying cause. However, data from NASA's Cassini spacecraft, which orbited Saturn between 2004 and 2017, introduced a new dimension. Observations revealed that Titan, Saturn's most significant moon, was receding from the planet faster than anticipated. This led scientists to ponder if Titan’s gravitational pull was the key behind Saturn's alignment with Neptune.
Yet, this posed another challenge: understanding Saturn's moment of inertia or the distribution of its mass. "To make progress on the problem, we had to determine the moment of inertia of Saturn,” says Wisdom.
Saturn evolution. (A and B) Obliquity of Saturn I (A), and the resonance angle σ (B), as a function of time t. The obliquity is with respect to the invariable plane, the plane perpendicular to the total angular momentum of the Solar System. (CREDIT: Science)
Harnessing data from Cassini’s "Grand Finale," the team derived a precise gravitational map of Saturn, enabling them to model the planet's interior and understand its mass distribution. Astonishingly, they discerned that Saturn's moment of inertia placed it just beyond resonance with Neptune, signifying that the two celestial bodies were no longer synchronized.
The Hunt for a Missing Link
Embarking on a journey to uncover how Saturn deviated from Neptune's resonance, the team scrutinized Saturn's historical orbital dynamics. Through meticulous calculations, they concluded that the removal of a moon – Chrysalis – from Saturn's gravitational equation could have been the pivotal factor. Chrysalis, comparable in size to Iapetus (Saturn's third-largest moon), ventured into a tumultuous orbital region, undergoing multiple encounters with Iapetus and Titan. This eventually led to its disastrous approach towards Saturn, culminating in its fragmentation.
Saturn's largest moon, Titan, is in the background of this image; in the foreground is the icy moon Dione. The much smaller moons Pandora and Pan sit near Saturn's bright rings, which slice through the center of the image. (CREDIT: NASA / JPL-Caltech / Space Science Institute)
The demise of Chrysalis, the team deduced, could elucidate Saturn’s precession, its modern-day tilt, and the belated creation of its iconic rings.
While Wisdom acknowledges the need for further exploration of their theory, he muses, “But it seems that this lost satellite was just a chrysalis, waiting to have its instability.”
Supported by both NASA and the National Science Foundation, this study marks a transformative moment in our understanding of the cosmos, exemplifying the continuous evolution of knowledge in our quest to decode the universe's mysteries.
For more science news stories check out our New Discoveries section at The Brighter Side of News.
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