Are Saturns Rings Vanishing? That Depends on Your Point of View
January 23, 20255 min readSaturns Rings Are DisappearingBut Theyll Be BackThis year, from Earths perspective, Saturns rings will appear nearly edge on, making them almost invisibleBy Phil Plait edited by Lee BillingsSaturns rings, imaged here by NASAs Cassini orbiter, are one of the solar systems most reliably spectacular sights. But sometimes they seem to disappear as seen from Earth. NASA/JPL/Space Science InstituteI recently noticed something odd about Saturn while admiring it near brilliant Venus in the southwestern night sky. Any object close to our evil twin sister planet will look somewhat dull in comparisonVenus can be so bright that its commonly mistaken for an airplane or a UFObut Saturn looked positively glum. Its almost on the other side of the sun from us right now, so its nearly at its maximum distance from Earth and thus somewhat fainter than usual. But still, it just seemed especially dim.Then I remembered: Saturns brilliant rings are disappearingat least they are from our perspective here on Earth. The normally broad rings presently appear much slimmer than usual, almost like a line across the planet. Without their countless reflective icy chunks adding to our view of Saturns luster, the planet really is less than half as bright as it can be at other times.Rest assured, Saturns magnificent rings are still there! There are two reasons theyre virtually invisible: one is that theyre almost unimaginably flat, and the other is that our viewing angle is affected by the dance of Saturns and Earths respective orbits.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Saturns rings are not just the most obvious thing about the planetthey are arguably the most magnificent structure in the entire solar system. The main rings are about 280,000 kilometers across; if you put them between Earth and the moon, theyd cover more than two thirds of that gap! At Saturns distance of more than a billion kilometers from Earth, the rings, as large as they are, are invisible to the unaided eyebut only just barely: as soon as we began scanning the sky with telescopes, the rings were spotted, even if their true structure remained mysterious.Galileo saw the rings through his crude telescope in the early 17th century but didnt have enough resolution to see their true shape, and he called them Saturns ears. Decades later Dutch astronomer Christiaan Huygens realized that the planet was encircled by a ring that was touching it nowhere, as he wrote in the book Systema Saturnium. A figure no less than physicist James Clerk Maxwellwho determined the equations for electromagnetism that underpin our technological civilizationwas the first to prove that such a ring couldnt be solid, or else it would get torn apart. The inner edge would revolve around Saturn much faster than the outer edge, shredding it. From this, it was found that the planets rings (plural) must be made up of chunks of material too small for any telescope from Earth to see. More modern observations showed that those chunks are nearly pure water icewhich is why theyre so bright; ice is an excellent reflector of sunlight. And modern studies also showed that most of these chunks are smaller than an average car. There must be quadrillions of them.Composed of Hubble Space Telescope images, this animation shows Earths changing perspective on Saturns rings between 2018 and 2024.NASA, ESA, Amy Simon (NASA-GSFC), Michael H. Wong (University of California), Joseph DePasquale (STScI)The rings probably formed from an icy moon of Saturn getting whacked, hard, by an incoming object, perhaps even another moon. Interestingly, its not clear when this happened. Research published in the journal Icarus in 2023 looked at the accumulation rate of dark micrometeorite dust on the otherwise shiny rings and found that the rings were young, cosmically speaking: just 100 million to 400 million years in age. On the other hand, research published in late 2024 in the journal Nature Geoscience found that the pollution rate from this dust isnt as fast as had been thought; the high-speed micrometeorite collisions ionize the ring particles, giving them an electric charge. That makes them susceptible to Saturns powerful magnetic field, which then draws the material away, slowing the rate at which the rings darken. That means the rings might be far older.Even today, centuries after their discovery, the rings still pose fundamental mysteries.Still, how they formed after the initial collision is relatively well understood, and it explains their flatness, if not their age. Because of the orbital motions of the Saturnian moon and its impactor, the debris would likely have first formed a long stream, most of which would have lain in the direction of that moons orbital motion. Saturns other moons orbit over its equator, so the material from this one would likely have wound up in a similar configuration as well. Also, because Saturn isnt a perfect sphere but instead bulges at the equator from its rapid 10.5-hour rotation period, the planets thickened middle would have torqued debris into an orbit directly over the equator; this is why a ring-generating impact would have formed a flat disk.And I do mean flat. Despite being hundreds of thousands of kilometers across, the rings are extremely thin, vertically spanning a kilometer at most. In some places the rings are just 10 meters high, as tall as a three-story building. As immense as the rings are, if they and Saturn itself were scaled down to 28 centimeters (11 inches) across, the length of a standard sheet of paper, the rings would be 100 times as thin as the paper! Finally, gravitational interactions with Saturns large moons pull those ring particles into slightly different orbits. Over time, they have created thousands of individual rings, as well as a handful of gaps among them. So from above, the rings are a source of slack-jawed awe. From the side, though, they are razor-thin and extremely difficult to see.Thats where we find ourselves now. Saturn, like Earth, has a large axial tilt that is more than 26 degrees askew from the ecliptic plane in which all the major planets orbit. (Earth has a 23-degree tilt.) This means that during Saturns northern summer, its north pole is tipped toward the sun. From Earth, much closer to the sun than Saturn, wed be looking down on the rings, seeing them in their full glory.Saturns orbit is just about 30 years long, so for much of the Saturnian year, we see the rings clearly. At the time of Saturns equinoxes, however, the rings are seen more nearly edge on from Earth, and in fact they are exactly edge on as seen from the sun. But because Saturns orbit around the sun is tipped very slightly relative to Earths, we only see the rings precisely edge on at Saturns equinox when Earth also passes through the plane of the rings. This can happen twice near the equinox as Earth passes up through the plane and then down again roughly six months later, effectively erasing Saturns rings from our view.And it just so happens that Saturns autumnal equinox will occur in May 2025. And on March 23 our planet will pass through the ring plane, so at that time, the rings will reach the peak of their vanishing act before slowly shifting back into view.But theres a caveat: on that date in March, Saturn will be only 10 degrees from the sun in the sky, making it very difficult to observe. Bad timing! While Saturn will pass through Earths orbital plane again in mid-November, by that time, Saturns axial tilt will have tipped the rings a bit from our vantage point, so well only see them very nearly edge on. The good news is that in November Saturn will be easily viewable in the southern sky after sunset, and it will still look nearly ringless through a telescope. Check to see if theres an observatory or astronomical society near you that is hosting a viewing session!Im hoping to take a gander myself; Saturn without rings will be delightfully odd, and its something I havent seen in more than seven years. But Ill also look forward to time marching on and the planet brightening once more as those glorious rings reveal themselves again. Somehow Saturn without them just wouldnt be Saturn.
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