By Pumudu Ramuditha
Saturn – the sixth planet from the Sun, the second biggest planet of the solar system, the planet with the lightest density; with many names, this Jovian giant is highlighted out from the rest of the planets by one striking feature – its spectacular ring system. They consist of countless ice and rock particles ranging from micrometers to meters in size, spread across multiple ring groups. Even though it’s been long discovered that the rest of the planets of the outer solar system have their ring systems as well, none is visible enough or visually appealing as the ones Saturn has.
Creation of Saturn’s ring system
Saturn’s rings are one of the most striking features in the Solar System. They consist of countless ice and rock particles ranging from micrometers to meters in size, spread across multiple ring groups. Their origin is still a subject of scientific debate, with several prevailing hypotheses. Currently, there are two leading hypotheses.
- The Primordial Hypothesis: In this, it’s believed that the rings formed during the creation of the planet itself, most possibly from the debris that were left after the formation of the planet, but failed to coalesce into a moon due to Saturn’s strong tidal forces. However, data received from the Cassini mission contradicts this hypothesis; that the rings seem to be relatively young, and formed after quite some time from the formation of Saturn.
- The Moon Disruption Hypothesis: This hypothesis suggests that the birth of the rings was caused by the disintegration of a moon or icy debris that once orbited around Saturn, yet got too close to the planet (near the Roche Limit) and was then ripped apart due to Saturn’s tidal forces. A version of this hypothesis, ‘’The Lost Moon Hypothesis’’, suggests that Saturn once had a large Titan-sized moon named Chrysalis, which’s orbit was unstabilized due to gravitational interactions with Saturn and Titan. It orbited too close to Saturn and was ripped apart around 160 million years ago, forming the rings. This hypothesis is backed by the data from the Cassini mission, which indicates that the ring material appears too clean for it to be billions of years old—if the rings were ancient, they should be more polluted with meteoric dust from the early solar system.
Despite its beauty and brightness, Saturn’s rings are incredibly thin and vast, with the main ring system spanning roughly 282,000 kilometers across, yet only about 100 meters thick in most places. But when observed through a telescope, an observer can still easily identify the rings of Saturn quite easily, even in small viewings where the rings can be viewed as ‘ears’ protruding from the sides of the planet, as per Galileo Galilei’s notes when he observed Saturn (his telescope wasn’t powerful enough for further detailed observations on the rings). But if you observe Saturn from a telescope at this current point in time, you would see a noticeable absence; the planet’s iconic rings would be nowhere in sight.
Saturn’s Ring Plane Crossing
Just like every other planet in the solar system, the rotating axis of Saturn is not exactly perpendicular to its orbit around the sun. In fact, Saturn’s axial tilt is about 26.7°; this causes its rings to appear at different inclinations over time when the planet continues its journey around the sun. As Saturn orbits the Sun (which takes about 29.5 Earth years per orbit), Earth crosses the plane of its rings about twice every 13 to 15 years. When Earth crosses this plane, the rings appear as a thin line slashed across the view of Saturn, or they could even seem to disappear completely due to their extremely thin structure (just around 30 meters thick even though spanning 282,000 km in width).
Last time this event occurred was in August 2009, where the rings almost completely disappeared from view. Before that, a rare three plane crossings happened in 1995-96 years. This event led astronomers to discover several new moons of Saturn that were previously obstructed from view due to the rings. However, the 2025 event is not in ideal observing conditions, as Saturn is still in its solar conjunction period; in which it’s partially obstructed from view due to the Sun’s glare. Its current close proximity to the sun acts as a major setback, but with powerful telescopes and advanced image capturing and enhancing softwares, obtaining a photograph of it wouldn’t be much difficult.
This event is also useful to scientists to measure the ring’s vertical thickness more accurately; since the previously mentioned value is a more generalized/mean value. Yet the thickness of the rings differ from region to region of these rings. As previously stated, the disappearance of Saturn’s rings makes Saturn’s smaller moons become more visible against the dark sky, allowing new moon discoveries (such as Pan and Daphnis) during observations. Also, by tracking the brightness variations of the rings, astronomers can understand how ring particles move and how the rings may evolve; through which the scientists discovered that Saturn’s rings are already in the process of disintegration, and that they may fade over the next 100 million years.