{"id":503529,"date":"2022-09-22T09:00:00","date_gmt":"2022-09-22T13:00:00","guid":{"rendered":"https:\/\/nspirement.com\/?p=503529"},"modified":"2022-09-22T04:32:01","modified_gmt":"2022-09-22T08:32:01","slug":"saturns-tilt-from-missing-moon","status":"publish","type":"post","link":"https:\/\/nspirement.com\/2022\/09\/22\/saturns-tilt-from-missing-moon.html","title":{"rendered":"Saturn\u2019s Rings and Tilt Could Be From an Ancient Missing Moon"},"content":{"rendered":"\n\n

Swirling around the planet\u2019s equator, the rings of Saturn <\/a>are a dead giveaway that the planet is spinning at a tilt. The belted giant rotates at a 26.7-degree angle relative to the plane in which it orbits the sun. Astronomers have long suspected that this tilt comes from gravitational interactions with its neighbor Neptune, as Saturn\u2019s tilt precesses, like a spinning top, at nearly the same rate as the orbit of Neptune.<\/p>\n\n\n\n

But a new modeling study<\/a> by astronomers at MIT and elsewhere has found that, while the two planets may have once been in sync, Saturn has since escaped Neptune\u2019s pull. What was responsible for this planetary realignment? The team has one meticulously tested hypothesis: a missing moon. In a study appearing<\/a> in Science<\/em>, the team proposes that Saturn, which today hosts 83 moons, once harbored at least one more, an extra satellite that they name Chrysalis. Together with its siblings, the researchers suggest, Chrysalis orbited Saturn for several billion years, pulling and tugging on the planet in a way that kept its tilt, or \u201cobliquity,\u201d in resonance with Neptune. <\/p>\n\n\n

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Researchers surmise, while most of Chrysalis\u2019 shattered body may have made an impact with Saturn, a fraction of its fragments could have remained suspended in orbit, eventually breaking into small icy chunks to form the planet\u2019s signature rings. (Image: Space Science Institute via NASA \/ JPL-Caltech)<\/figcaption><\/figure><\/div>\n\n\n

But around 160 million years ago, the team estimates, Chrysalis became unstable and came too close to its planet in a grazing encounter that pulled the satellite apart. The loss of the moon was enough to remove Saturn from Neptune\u2019s grasp and leave it with the present-day tilt. What\u2019s more, the researchers surmise, while most of Chrysalis\u2019 shattered body may have impacted Saturn, a fraction of its fragments could have remained suspended in orbit, eventually breaking into small icy chunks to form the planet\u2019s signature rings. The missing satellite, therefore, could explain two longstanding mysteries: Saturn\u2019s present-day tilt and the age of its rings, which were previously estimated to be about 100 million years old \u2014 much younger than the planet itself. Jack Wisdom, professor of planetary sciences at MIT and lead author of the new study, said:<\/p>\n\n\n\n

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\u201cJust like a butterfly\u2019s chrysalis, this satellite was long dormant and suddenly became active, and the rings emerged.\u201d <\/p><\/blockquote>\n<\/div><\/div>\n\n\n\n

A moment of progress<\/h2>\n\n\n\n

In the early 2000s, scientists put forward the idea that Saturn\u2019s tilted axis is a result of the planet being trapped in resonance, or gravitational association, with Neptune. But observations taken by NASA\u2019s Cassini spacecraft, which orbited Saturn from 2004 to 2017, put a new twist on the problem. Scientists found that Titan, the planet’s largest satellite, was migrating away at a faster clip than expected, at a rate of about 11 centimeters per year. Titan\u2019s fast migration, and its gravitational pull, led scientists to conclude that the moon was likely responsible for tilting and keeping the planet in resonance with Neptune.<\/p>\n\n\n\n

But this explanation hinges on one major unknown: Saturn\u2019s moment of inertia, which is how mass is distributed in the planet\u2019s interior. Saturn\u2019s tilt could behave differently, depending on whether matter is more concentrated at its core or toward the surface, Wisdom said:<\/p>\n\n\n\n

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\u201cTo make progress on the problem, we had to determine the moment of inertia of Saturn.\u201d<\/p><\/blockquote>\n<\/div><\/div>\n\n\n\n

The lost element<\/h2>\n\n\n\n

In their new study, Wisdom and his colleagues looked to pin down Saturn\u2019s moment of inertia using some of the last observations taken by Cassini in its “Grand Finale,” a phase of the mission during which the spacecraft made an extremely close approach to precisely map the gravitational field around the entire planet.\u00a0The gravitational field can be used to determine the distribution of mass on the planet.<\/p>\n\n\n

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The question was, how massive would that satellite have to be, and what dynamics would it have to undergo to take Saturn out of Neptune\u2019s resonance? (Image: Space Science Institute via NASA \/ JPL-Caltech<\/figcaption><\/figure><\/div>\n\n\n

Wisdom and his colleagues modeled the interior of Saturn and identified a distribution of mass that matched the gravitational field that Cassini observed. Surprisingly, they found that this newly identified moment of inertia placed Saturn close to, but just outside, its resonance with Neptune. The planets may have once been in sync, but are no longer. Wisdom said:<\/p>\n\n\n\n

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\u201cThen we went hunting for ways of getting Saturn out of Neptune\u2019s resonance.\u201d <\/p><\/blockquote>\n<\/div><\/div>\n\n\n\n

Saturn’s tilt<\/h2>\n\n\n\n

The team first carried out simulations to evolve the orbital dynamics of Saturn and its moons backward in time, to see whether any natural instabilities among the existing satellites could have influenced the planet\u2019s tilt. This search came up empty. So, the researchers reexamined the mathematical equations that describe a planet\u2019s precession, which is how a planet\u2019s axis of rotation changes over time. One term in this equation has contributions from all the satellites. The team reasoned that if one satellite were removed from this sum, it could affect the planet\u2019s precession.<\/p>\n\n\n

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In the early 2000s, scientists put forward the idea that Saturn\u2019s tilted axis is a result of the planet being trapped in resonance, or gravitational association, with Neptune. (Image: A. Simon (GSFC), M.H. Wong (University of California, Berkeley), and the OPAL Team via NASA, ESA)<\/figcaption><\/figure><\/div>\n\n\n

The question was, how massive would that satellite have to be, and what dynamics would it have to undergo to take Saturn out of Neptune\u2019s resonance? Wisdom and his colleagues ran simulations to determine the properties of a satellite, such as its mass and orbital radius, and the orbital dynamics that would be required to knock Saturn out of the resonance. They conclude that the planet’s present tilt is the result of the resonance with Neptune and that the loss of the satellite, Chrysalis, which was about the size of Iapetus, Saturn\u2019s third-largest moon, allowed it to escape the resonance.<\/p>\n\n\n\n

Sometime between 200 and 100 million years ago, Chrysalis entered a chaotic orbital zone, experienced a number of close encounters with Iapetus and Titan, and eventually came too close to Saturn, in a grazing encounter that ripped the satellite to bits, leaving a small fraction to circle the planet as a debris-strewn ring. The loss of Chrysalis, they found, explains Saturn\u2019s precession, and its present-day tilt, as well as the late formation of its rings, Wisdom said:<\/p>\n\n\n\n

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\u201cIt\u2019s a pretty good story, but like any other result, it will have to be examined by others. But it seems that this lost satellite was just a chrysalis, waiting to have its instability.\u201d<\/p><\/blockquote>\n<\/div><\/div>\n\n\n\n

Provided by Jennifer Chu, Massachusetts Institute of Technology<\/a> [Note: Materials may be edited for content and length.]<\/em><\/p>\n\n\n\n

Follow us on <\/em><\/strong>Twitter<\/em><\/strong><\/a>, <\/em><\/strong>Facebook<\/em><\/strong><\/a>, or <\/em><\/strong>Pinterest<\/em><\/strong><\/a><\/em><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

Swirling around the planet\u2019s equator, the rings of Saturn are a dead giveaway that the planet is spinning at a tilt. The belted giant rotates at a 26.7-degree angle relative to the plane in which it orbits the sun. Astronomers have long suspected that this tilt comes from gravitational interactions with its neighbor Neptune, as … Read More<\/a><\/p>\n","protected":false},"author":391,"featured_media":503530,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6712],"tags":[39191,13898,9172,28042,39190,5938],"ppma_author":[27955],"pp_statuses_selecting_workflow":false,"pp_workflow_action":"current","pp_status_selection":"publish","authors":[{"term_id":27955,"user_id":391,"is_guest":0,"slug":"troy-o","display_name":"Troy Oakes","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/4cbde84ab42a0f157dce2a1b93e5596c?s=96&d=mm&r=g","last_name":"Oakes","user_url":"","first_name":"Troy","description":"Troy was born and raised in Australia and has always wanted to know why and how things work, which led him to his love for science. He is a professional photographer and enjoys taking pictures of Australia's beautiful landscapes. He is also a professional storm chaser where he currently lives in Hervey Bay, Australia."}],"_links":{"self":[{"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/posts\/503529"}],"collection":[{"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/users\/391"}],"replies":[{"embeddable":true,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/comments?post=503529"}],"version-history":[{"count":3,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/posts\/503529\/revisions"}],"predecessor-version":[{"id":504311,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/posts\/503529\/revisions\/504311"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/media\/503530"}],"wp:attachment":[{"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/media?parent=503529"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/categories?post=503529"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/tags?post=503529"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/nspirement.com\/wp-json\/wp\/v2\/ppma_author?post=503529"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}