Rings of Saturn

Saturn has the biggest and most complicated ring system of any planet in the Solar System. The rings are made of tiny pieces of water ice and some rock. These pieces range from very small to as big as buildings. They orbit around Saturn in a flat, wide circle.

The full set of rings, imaged on 19 July 2013, as Saturn eclipses the Sun from the vantage of the Cassini orbiter, which is 1.2 million kilometres (3⁄4 million miles) from Saturn. Earth appears as a dot at 4 o'clock, between the G and E rings – with its brightness artificially exaggerated in this photograph.

Even though the rings make Saturn look brighter, we can't see them with just our eyes from Earth. In 1610, the scientist Galileo Galilei was the first to see Saturn’s rings using a telescope, but he didn’t know exactly what they were. Later, in 1655, Christiaan Huygens correctly described them as a disk around the planet. Scientists found that the rings are split into many smaller parts called ringlets.

The rings have gaps with fewer particles. Some gaps are made by Saturn’s moons, and others happen because of how the moons’ orbits affect the rings. There is also a faraway ring called the Phoebe ring, which comes from a moon named Phoebe and moves in the opposite direction to Saturn’s other rings. Scientists are still trying to figure out how old the rings are. Some think they are very old, while others believe they might be much younger.

History

Early observations

Detail of Galileo's drawing of Saturn in a letter to Belisario Vinta (1610)

Galileo Galilei was the first person to see Saturn's rings in 1610 using a telescope. He saw them as three objects close together and wondered if Saturn had "swallowed its children," based on an old story. Later, the rings disappeared from view and then reappeared, which puzzled early scientists.

Other early scientists tried to explain what they saw. Some thought the rings might be connected to the planet, while others had different ideas.

Huygens' ring hypothesis and later developments

Huygens' ring hypothesis in Systema Saturnium (1659)

Christiaan Huygens improved telescope technology and, in 1659, suggested that Saturn was surrounded by a thin, flat ring not touching the planet. This idea was accepted and explained many observations.

Later scientists discovered that Saturn's rings are made of many small particles and have gaps between them. Spacecraft like Pioneer 11, Voyager 1, Voyager 2, and Cassini provided detailed images, showing the complex structure of the rings and discovering new parts of the system.

Observation

Saturn's tilt is 26.7°, which means we can see its rings from different angles at different times. Earth passes through the plane of Saturn's rings every 13 to 15 years. The last times this happened were on 22 May 1995, 10 August 1995, 11 February 1996, 4 September 2009 and 23 March 2025. The next times will be on 15 October 2038, 1 April 2039 and 9 July 2039.

When the Sun passes through the plane of Saturn's rings, called an equinox, we get special chances to see the rings clearly. The Sun moves north to south through the rings when Saturn is at a certain position, and then south to north about 15.7 years later. During these times, the rings are less bright, allowing us to see details better.

General characteristics

The rings of Saturn stretch from about 7,000 kilometers to 80,000 kilometers from the planet's equator. These rings are very thin, only about 10 meters to 1 kilometer thick. They are made mostly of pure water ice, with a few bits of other materials. The pieces in the rings range from very tiny to smaller than 10 meters across.

The Cassini spacecraft measured the mass of the rings by studying their effect on nearby space. The rings have a mass of about two-thirds that of Earth's Antarctic ice sheet, but spread over an area 80 times larger. The rings also have a very thin atmosphere made of oxygen and hydrogen, created when sunlight breaks apart water ice in the rings.

Formation and evolution of main rings

The age of Saturn's rings is still a mystery. Some think they might be as old as Saturn itself, but data from the Cassini spacecraft suggests they are much younger, perhaps only 10 to 100 million years old. This idea comes from measuring how much material the rings lose over time. Since the rings are losing material, they would have been bigger in the past.

A 2007 artist's impression of the aggregates of icy particles that form the portions of Saturn's rings which appear solid from a distance. These elongated clumps are continually forming and dispersing. The largest particles are a few meters across.

One theory is that the rings came from a broken moon. A long time ago, a moon might have gotten too close to Saturn and was torn apart by strong forces. Another idea is that a moon broke apart after being hit by a large comet or asteroid. In 2023, studies showed that two icy moons crashing could also explain why there is so little rock in the rings.

The bright, clean ice in the rings might also point to them being young. Over time, dust would make the rings darker, but new research shows some parts of the rings might be big enough to keep staying bright. Some parts of the rings might be as young as 100 million years old if they came from a recently broken moon or object.

Research also shows that material from the rings is slowly falling into Saturn. If this continues, the rings might disappear in less than 100 million years.

Physical structure of the rings

The thickest parts of Saturn's rings are called the A and B Rings. Between them is a gap called the Cassini Division. It was found in 1675 by Giovanni Domenico Cassini. With the C Ring, found in 1850, these make up the main rings. They are thicker and have bigger pieces than the thinner, dusty rings. The dusty rings include the D Ring, which is close to Saturn, and the G and E Rings, among others. They are called dusty because their pieces are very small, often about a μm across. Like the main rings, they are mostly made of water ice. The narrow F Ring, just outside the A Ring, is special—it has dense parts and many tiny particles.

Name	Distance from Saturn's center (km)	Width (km)	Thickness (m)
D Ring	66,900 –76,517	7,500
C Ring	74,658 – 92,000	17,500	5
B Ring	92,000 –117,580	25,500	5-15
Cassini Division	117,580 –122,170	4,700
A Ring	122,170 –136,775	14,600	10-30
Roche Division	136,775 – 139,380	2,600
F Ring	140,180	30 – 500
Janus/Epimetheus Ring	149,000 – 154,000	5,000
G Ring	166,000 –175,000	9,000
Methone Ring Arc	194,230	?
Anthe Ring Arc	197,665	?
Pallene Ring	211,000 – 213,500	2,500
E Ring	180,000 – 480,000	300,000	>2000 km
Phoebe Ring	~4,000,000 – >13,000,000	9,900,000 –12,800,000	2,330,000 km

Name	Distance from Saturn's center (km)	Width (km)	Named after
Colombo Gap	77,870	150	Giuseppe "Bepi" Colombo
Titan Ringlet	77,870	25	Titan, moon of Saturn
Maxwell Gap	87,491	270	James Clerk Maxwell
Maxwell Ringlet	87,491	64	James Clerk Maxwell
Bond Gap	88,700	30	William Cranch Bond and George Phillips Bond
1.470R_S Ringlet	88,716	16	its radius
1.495R_S Ringlet	90,171	62	its radius
Dawes Gap	90,210	20	William Rutter Dawes

Name	Distance from Saturn's center (km)	Width (km)	Named after
Huygens Gap	117,680	285–400	Christiaan Huygens
Huygens Ringlet	117,848	~17	Christiaan Huygens
Herschel Gap	118,234	102	William Herschel
Russell Gap	118,614	33	Henry Norris Russell
Jeffreys Gap	118,950	38	Harold Jeffreys
Kuiper Gap	119,405	3	Gerard Kuiper
Laplace Gap	119,967	238	Pierre-Simon Laplace
Bessel Gap	120,241	10	Friedrich Bessel
Barnard Gap	120,312	13	Edward Emerson Barnard

Name	Distance from Saturn's center (km)	Width (km)	Named after
Encke Gap	133,589	325	Johann Encke
Keeler Gap	136,505	35	James Keeler

D Ring

The D Ring is the innermost ring of Saturn and is very faint. In 1980, Voyager 1 found three small sections within this ring, called D73, D72, and D68, with D68 being the closest to Saturn. Later images from Cassini showed that D72 had grown wider and spread out, moving closer to the planet.

A Cassini image of the faint D Ring, with the inner C Ring below

The D Ring has a fine pattern with waves about 30 km apart. These waves were first seen between the C Ring and D73 and later found to stretch a long distance from the D Ring to the B Ring. Scientists think these waves are like a spiral pattern. A similar pattern exists in Jupiter's main ring after material from Comet Shoemaker-Levy 9 hit Jupiter.

C Ring

The C Ring is a wide but faint ring inside the B Ring. It was found in 1850 by William and George Bond, with William R. Dawes and Johann Galle also seeing it. William Lassell called it the "Crepe Ring" because it looked like darker material than the brighter A and B Rings.

The C Ring is very thin, about 5 meters thick. Light passing through it is only partly blocked, so the ring looks almost see-through. Special patterns in the ring were seen in 2009.

View of the outer C Ring; the Maxwell Gap with the Maxwell Ringlet on its right side are above and right of center. The Bond Gap is above a broad light band towards the upper right; the Dawes Gap is within a dark band just below the upper right corner.

Colombo Gap and Titan Ringlet

The Colombo Gap is a space in the inner part of the C Ring. Inside this gap is a bright, narrow area called the Colombo Ringlet, located about 77,883 kilometers from Saturn’s center. This area is slightly stretched out. It is also called the Titan Ringlet because it is linked to the moon Titan.

Maxwell Gap and Ringlet

The Maxwell Gap is in the outer part of the C Ring. Inside this gap is a dense area called the Maxwell Ringlet. This ringlet shares some features with a ring around Uranus. Both have wave-like patterns in the middle. The cause of the wave in Uranus’s ring is a moon called Cordelia, but no moon has been found in the Maxwell gap as of July 2008.

B Ring

The B Ring is the largest, brightest ring around Saturn. It is about 5 to 15 meters thick and can block most of the light passing through it. The B Ring changes in ways that are not fully understood.

The B Ring sometimes has tall structures that rise up to 2.5 kilometers. These structures might be caused by small, unseen moons within the ring. Studies show that the B Ring has less mass than we thought, with its total mass estimated to be between 7 and 24 times 10¹⁸ kilograms.

Spokes

Before 1980, scientists thought the rings' structure was only due to gravity. But images from the Voyager spacecraft showed features called "spokes" in the B Ring. These spokes appear dark in some light and bright in other light. Scientists think the spokes might be tiny dust particles lifted away from the ring by electric forces. The exact cause of the spokes is still a mystery.

The spokes were seen again by the Cassini spacecraft in 2005, after being missing for many years. They seem to appear and disappear with Saturn's seasons, showing up when Saturn is near an equinox.

Moonlet

In 2009, during an equinox, a small moon embedded in the B Ring was discovered by the shadow it cast. This moonlet is estimated to be about 400 meters in diameter and was given the provisional designation S/2009 S 1.

Cassini Division

The Cassini Division is a wide space, about 4,800 kilometers across, between two of Saturn’s rings, called the A Ring and the B Ring. It was first seen in 1675 by an astronomer named Giovanni Cassini using a telescope. From Earth, it looks like a thin dark line in the rings. But space probes showed that this area still has ring material, similar to another part of the rings called the C Ring.

The inner edge of the Cassini Division is affected by the gravity of a moon called Mimas. This creates a sharp drop in how many particles are there. Some smaller gaps inside the Cassini Division are still not fully understood.

A Ring

The A Ring is the outermost of Saturn's bright rings. It starts at the Cassini Division and ends near the orbit of the small moon Atlas. There are two notable gaps in this ring: the Encke Gap and the Keeler Gap.

The Encke Gap is wide and is kept clear by the small moon Pan. The Keeler Gap is narrower and is cleared by the moon Daphnis.

Roche Division

The space between the A ring and the F Ring is called the Roche Division. It is named after a French scientist named Édouard Roche. This area is close to Saturn, where big objects might be pulled apart by the planet's strong forces.

The Roche Division is not empty. It has a thin layer of material, like the faint D, E, and G Rings. Two spots in this area have more dust than others. These spots were found by the Cassini probe and given temporary names: R/2004 S 1, near the moon Atlas, and R/2004 S 2, about 138,900 kilometers from Saturn’s center, inside the path of the moon Prometheus.

F Ring

The F Ring is the outermost ring of Saturn and one of the most active in the Solar System. It was discovered in 1979 by the Pioneer 11 and is located about 3,000 km beyond the edge of the A ring. This ring is very thin, stretching just a few hundred kilometers wide.

Recent studies show that the F Ring has a core ring with a spiral strand around it. The moon Prometheus affects the ring strongly, creating twists and knots as it moves close to the ring. These changes happen quickly, with new patterns forming every few hours. Scientists believe many small objects within the ring are constantly moving, which helps keep the ring looking the way it does today.

Outer rings

Janus/Epimetheus Ring

A thin ring of dust surrounds the area where the moons Janus and Epimetheus travel. It was found by the Cassini spacecraft in 2006. The dust comes from tiny pieces that break off these moons when hit by small space rocks.

G Ring

The G Ring is a thin and faint ring between the F Ring and the E Ring. It has a brighter part near its inner edge, which is linked to a small moon called Aegaeon. This moon helps keep the brighter part in place. The ring is made of tiny ice pieces and dust.

Methone Ring Arc

In 2006, a faint ring arc was found near the moon Methone. This arc of dust is thought to come from particles that break off Methone when hit by tiny space rocks. The arc stays in place because of the gravitational pull of another moon, Mimas.

Anthe Ring Arc

A faint ring arc was discovered near the moon Anthe in 2007. Like the arc near Methone, this dust likely comes from particles breaking off Anthe due to tiny space rocks. The arc’s position is controlled by the gravitational influence of Mimas.

Pallene Ring

Images from the Cassini spacecraft in 2006 showed a thin ring of dust that shares the same path as the moon Pallene. This dust is probably material that has been knocked off Pallene by tiny space rocks.

E Ring

The E Ring is a wide ring made of very small pieces of water ice. It was confirmed to exist in 1980, though people had seen something like it earlier. The material in this ring comes from geysers that shoot ice particles into space from the south pole of the moon Enceladus. Because the particles are so tiny, the ring is very thick and can be seen best when viewed from the side.

Phoebe ring

In 2009, a very thin and wide ring was discovered inside the orbit of the moon Phoebe. This ring is so faint that it is almost invisible. It was found using a telescope that can see heat. The ring’s particles are thought to come from Phoebe itself, broken off by tiny space rocks. The ring is tilted compared to Saturn’s other rings and stretches very far from the planet.