A ring system is a disc or torus orbiting an astronomical object that is composed of solid material such as gas, dust , meteoroids , planetoids or moonlets and stellar objects.
98-499: The rings of Saturn are the most extensive and complex ring system of any planet in the Solar System . They consist of countless small particles, ranging in size from micrometers to meters , that orbit around Saturn . The ring particles are made almost entirely of water ice, with a trace component of rocky material . There is still no consensus as to their mechanism of formation. Although theoretical models indicated that
196-1039: A substellar object with a circumstellar disk or massive rings transiting the star. This substellar object, dubbed " J1407b ", is most likely a free-floating brown dwarf or rogue planet several times the mass of Jupiter. The circumstellar disk or ring system of J1407b is about 0.6 astronomical units (90,000,000 km; 56,000,000 mi) in radius. J1407b's transit of V1400 Centauri revealed gaps and density variations within its disk or ring system, which has been interpreted as hints of exomoons or exoplanets forming around J1407b. Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". Christiaan Huygens Too Many Requests If you report this error to
294-420: A better hypothesis than his own and De corpore saturni was never published. Robert Hooke was another early observer of the rings of Saturn, and noted the casting of shadows on the rings. Huygens began grinding lenses with his father Constantijn in 1655 and was able to observe Saturn with greater detail using a 43× power refracting telescope that he designed himself. He was the first to suggest that Saturn
392-477: A considerable risk to the New Horizons spacecraft. However, this possibility was ruled out when New Horizons failed to detect any dust rings around Pluto. 10199 Chariklo , a centaur , was the first minor planet discovered to have rings. It has two rings , perhaps due to a collision that caused a chain of debris to orbit it. The rings were discovered when astronomers observed Chariklo passing in front of
490-462: A deduction that the pattern may have originated in late 1983 with the impact of a cloud of debris (with a mass of ≈10 kg) from a disrupted comet that tilted the rings out of the equatorial plane. A similar spiral pattern in Jupiter's main ring has been attributed to a perturbation caused by impact of material from Comet Shoemaker-Levy 9 in 1994. The C Ring is a wide but faint ring located inward of
588-428: A distance of 4,057 ± 6 km , approximately 7.5 times the radius of Quaoar and more than double the distance of its Roche limit. The inner ring orbits at a distance of 2,520 ± 20 km , approximately 4.6 times the radius of Quaoar and also beyond its Roche limit. The outer ring appears to be inhomogeneous, containing a thin, dense section as well as a broader, more diffuse section. Because all giant planets of
686-585: A distinctive band around the Earth's equator at that time. The presence of this ring may have led to significant shielding of Earth from sun's rays and a severe cooling event, thus causing the Hirnantian glaciation , the coldest known period of the last 450 million years. Reports in March 2008 suggested that Saturn's moon Rhea may have its own tenuous ring system , which would make it the only moon known to have
784-473: A form of commitment scheme to lay claim to new discoveries before their results were ready for publication. Galileo used the anagram " smaismrmilmepoetaleumibunenugttauiras " for Altissimum planetam tergeminum observavi ("I have observed the most distant planet to have a triple form") for discovering the rings of Saturn. In 1657 Christopher Wren became Professor of Astronomy at Gresham College, London. He had been making observations of
882-482: A gaseous nebula. This would explain the scarcity of rocky material within the rings. The rings would initially have been much more massive (≈1,000 times) and broader than at present; material in the outer portions of the rings would have coalesced into the innermost moons of Saturn (those closest to Saturn), out to Tethys , also explaining the lack of rocky material in the composition of most of these moons. Subsequent collisional or cryovolcanic evolution of Enceladus, which
980-479: A moon that large was during the Late Heavy Bombardment some four billion years ago. A more recent variant of this type of theory by R. M. Canup is that the rings could represent part of the remains of the icy mantle of a much larger, Titan-sized, differentiated moon that was stripped of its outer layer as it spiraled into the planet during the formative period when Saturn was still surrounded by
1078-469: A moon that was disrupted by tidal stresses when it passed within the planet's Roche limit. Most rings were thought to be unstable and to dissipate over the course of tens or hundreds of millions of years, but it now appears that Saturn's rings might be quite old, dating to the early days of the Solar System. Fainter planetary rings can form as a result of meteoroid impacts with moons orbiting around
SECTION 10
#17327720296841176-414: A more complicated set. It is primarily acted on by the 7:6 resonance with Janus and Epimetheus , with other contributions from the 5:3 resonance with Mimas and various resonances with Prometheus and Pandora . Other orbital resonances also excite many spiral density waves in the A Ring (and, to a lesser extent, other rings as well), which account for most of its structure. These waves are described by
1274-513: A planetary ring in about 50 million years. Its low orbit, with an orbital period that is shorter than a Martian day, is decaying due to tidal deceleration . Jupiter's ring system was the third to be discovered, when it was first observed by the Voyager 1 probe in 1979, and was observed more thoroughly by the Galileo orbiter in the 1990s. Its four main parts are a faint thick torus known as
1372-404: A ring mass of 0.1%−10% of the centaur's mass is predicted. Ring formation from an undifferentiated body is less likely. The rings would be composed mostly or entirely of material from the parent body's icy mantle. After forming, the ring would spread laterally, leading to satellite formation from whatever portion of it spreads beyond the centaur's Roche Limit. Satellites could also form directly from
1470-468: A ring particle is determined by the specific strength of the material it is made of, its density, and the tidal force at its altitude. The tidal force is proportional to the average density inside the radius of the ring, or to the mass of the planet divided by the radius of the ring cubed. It is also inversely proportional to the square of the orbital period of the ring. Some planetary rings are influenced by shepherd moons , small moons that orbit near
1568-492: A ring system for a period of 40 million years, starting from the middle of the Ordovician period (around 466 million years ago). This ring system may have originated from a large asteroid that passed by Earth at this time and had a significant amount of debris stripped by Earth's gravitational pull, forming a ring system. Evidence for this ring comes from impact craters from the Ordovician meteor event appearing to cluster in
1666-576: A ring system. A later study published in 2010 revealed that imaging of Rhea by the Cassini spacecraft was inconsistent with the predicted properties of the rings, suggesting that some other mechanism is responsible for the magnetic effects that had led to the ring hypothesis. Prior to the arrival of New Horizons , some astronomers hypothesized that Pluto and Charon might have a circumbinary ring system created from dust ejected off of Pluto's small outer moons in impacts. A dust ring would have posed
1764-438: A series of tiny ringlets as many think, but are more of a disk with varying density. They consist mostly of water ice and trace amounts of rock , and the particles range in size from micrometers to meters. Uranus's ring system lies between the level of complexity of Saturn's vast system and the simpler systems around Jupiter and Neptune. They were discovered in 1977 by James L. Elliot , Edward W. Dunham, and Jessica Mink . In
1862-565: A sharp cutoff in ring density. Many of the other gaps between ringlets within the Cassini Division, however, are unexplained. Discovered in 1981 through images sent back by Voyager 2, the Huygens Gap is located at the inner edge of the Cassini Division. It contains the dense, eccentric Huygens Ringlet in the middle. This ringlet exhibits irregular azimuthal variations of geometrical width and optical depth, which may be caused by
1960-465: A single or three crossings occurring in each such occasion. The most recent ring plane crossings were on 22 May 1995, 10 August 1995, 11 February 1996 and 4 September 2009; upcoming events will occur on 23 March 2025, 15 October 2038, 1 April 2039 and 9 July 2039. Favorable ring plane crossing viewing opportunities (with Saturn not close to the Sun) only come during triple crossings. Saturn's equinoxes , when
2058-402: Is 60,300 km (37,500 mi) (see Major subdivisions ). With an estimated local thickness of as little as 10 metres (32' 10") and as much as 1 km (1093 yards), they are composed of 99.9% pure water ice with a smattering of impurities that may include tholins or silicates . The main rings are primarily composed of particles smaller than 10 m. Cassini directly measured the mass of
SECTION 20
#17327720296842156-525: Is a region 4,800 km (3,000 mi) in width between Saturn's A Ring and B Ring . It was discovered in 1675 by Giovanni Cassini at the Paris Observatory using a refracting telescope that had a 2.5-inch objective lens with a 20-foot-long focal length and a 90x magnification . From Earth it appears as a thin black gap in the rings. However, Voyager discovered that the gap is itself populated by ring material bearing much similarity to
2254-564: Is about 1,000 times closer than the Moon is to Earth. In addition, astronomers suspect there could be a moon orbiting amidst the ring debris. If these rings are the leftovers of a collision as astronomers suspect, this would give fodder to the idea that moons (such as the Moon) form through collisions of smaller bits of material. Chariklo's rings have not been officially named, but the discoverers have nicknamed them Oiapoque and Chuí, after two rivers near
2352-503: Is also present. The O 2 and H 2 atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be about one atom thick. The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O 2 , this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic ions that bombard water molecules ejected by Saturn's moon Enceladus . This atmosphere, despite being extremely sparse,
2450-505: Is another of these moons, might then have caused selective loss of ice from this moon, raising its density to its current value of 1.61 g/cm, compared to values of 1.15 for Mimas and 0.97 for Tethys. The idea of massive early rings was subsequently extended to explain the formation of Saturn's moons out to Rhea. If the initial massive rings contained chunks of rocky material (>100 km; 60 miles across) as well as ice, these silicate bodies would have accreted more ice and been expelled from
2548-465: Is slightly elliptical rather than circular. This ringlet is also called the Titan Ringlet as it is governed by an orbital resonance with the moon Titan . At this location within the rings, the length of a ring particle's apsidal precession is equal to the length of Titan's orbital motion, so that the outer end of this eccentric ringlet always points towards Titan. The Maxwell Gap lies within
2646-501: Is that this moon disintegrated after being struck by a large comet or asteroid . The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material from which Saturn formed. A more traditional version of the disrupted-moon theory is that the rings are composed of debris from a moon 400 to 600 km (200 to 400 miles) in diameter, slightly larger than Mimas . The last time there were collisions large enough to be likely to disrupt
2744-450: Is the innermost ring, and is very faint. In 1980, Voyager 1 detected within this ring three ringlets designated D73, D72 and D68, with D68 being the discrete ringlet nearest to Saturn. Some 25 years later, Cassini images showed that D72 had become significantly broader and more diffuse, and had moved planetward by 200 km (100 miles). Present in the D Ring is a finescale structure with waves 30 km (20 miles) apart. First seen in
2842-412: Is tilted at an angle of 27 degrees to the more visible rings orbiting above Saturn's equator. In September 2023, astronomers reported studies suggesting that the rings of Saturn may have resulted from the collision of two moons "a few hundred million years ago". Galileo Galilei was the first to observe the rings of Saturn in 1610 using his telescope, but was unable to identify them as such. He wrote to
2940-502: Is well within Haumea's Roche limit , which would lie at a radius of about 4,400 km if Haumea were spherical (being nonspherical pushes the limit out farther). In 2023, astronomers announced the discovery of a widely separated ring around the dwarf planet and Kuiper belt object Quaoar . Further analysis of the occultation data uncovered a second inner, fainter ring. Both rings display unusual properties. The outer ring orbits at
3038-497: The B Ring . It was discovered in 1850 by William and George Bond , though William R. Dawes and Johann Galle also saw it independently. William Lassell termed it the "Crepe Ring" because it seemed to be composed of darker material than the brighter A and B Rings. Its vertical thickness is estimated at 5 metres (16'), its mass at around 1.1 × 10 kg, and its optical depth varies from 0.05 to 0.12. That is, between 5 and 12 percent of light shining perpendicularly through
Rings of Saturn - Misplaced Pages Continue
3136-514: The C Ring . The division may appear bright in views of the unlit side of the rings, since the relatively low density of material allows more light to be transmitted through the thickness of the rings (see second image in gallery ). The inner edge of the Cassini Division is governed by a strong orbital resonance. Ring particles at this location orbit twice for every orbit of the moon Mimas . The resonance causes Mimas' pulls on these ring particles to accumulate, destabilizing their orbits and leading to
3234-512: The Cassini Division . This division is a 4,800-kilometre-wide (3,000 mi) region between the A ring and B Ring . In 1787, Pierre-Simon Laplace proved that a uniform solid ring would be unstable and suggested that the rings were composed of a large number of solid ringlets. In 1859, James Clerk Maxwell demonstrated that a nonuniform solid ring, solid ringlets or a continuous fluid ring would also not be stable, indicating that
3332-641: The Cassini Titan Radar Mapper , which focused on analyzing the proportion of rocky silicates within this ring. If much of this material was contributed by a recently disrupted centaur or moon, the age of this ring could be on the order of 100 million years or less. On the other hand, if the material came primarily from micrometeoroid influx, the age would be closer to a billion years. The Cassini UVIS team, led by Larry Esposito , used stellar occultation to discover 13 objects, ranging from 27 metres (89') to 10 km (6 miles) across, within
3430-456: The Duke of Tuscany that "The planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the zodiac , and the middle one (Saturn itself) is about three times the size of the lateral ones." He also described the rings as Saturn's "ears". In 1612 the Earth passed through the plane of
3528-540: The Encke Gap . A narrower gap 2% of the ring width from the outer edge is called the Keeler Gap . The thickness of the A Ring is estimated to be 10 to 30 m, its surface density from 35 to 40 g/cm and its total mass as 4 to 5 × 10 kg (just under the mass of Hyperion ). Its optical depth varies from 0.4 to 0.9. Similarly to the B Ring, the A Ring's outer edge is maintained by orbital resonances, albeit in this case
3626-470: The F ring . They are translucent, suggesting they are temporary aggregates of ice boulders a few meters across. Esposito believes this to be the basic structure of the Saturnian rings, particles clumping together, then being blasted apart. Research based on rates of infall into Saturn favors a younger ring system age of hundreds of millions of years. Ring material is continually spiraling down into Saturn;
3724-558: The Voyager spacecraft discovered that the rings have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise, in several different ways, from the gravitational pull of Saturn's many moons. Some gaps are cleared out by the passage of tiny moonlets such as Pan , many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small shepherd satellites (similar to Prometheus and Pandora 's maintenance of
3822-599: The asteroid belt or Kuiper belt , or rings of interplanetary dust , such as around the Sun at distances of Mercury , Venus , and Earth, in mean motion resonance with these planets. Evidence suggests that ring systems may also be found around other types of astronomical objects, including moons and brown dwarfs . In the Solar System , all four giant planets ( Jupiter , Saturn, Uranus , and Neptune ) have ring systems. Ring systems around minor planets have also been discovered via occultations. Some studies even theorize that
3920-555: The moons of Saturn . Other gaps remain unexplained. Stabilizing resonances, on the other hand, are responsible for the longevity of several rings, such as the Titan Ringlet and the G Ring . Well beyond the main rings is the Phoebe ring , which is presumed to originate from Phoebe and thus share its retrograde orbital motion. It is aligned with the plane of Saturn's orbit. Saturn has an axial tilt of 27 degrees, so this ring
4018-439: The "halo"; a thin, relatively bright main ring; and two wide, faint "gossamer rings". The system consists mostly of dust. Saturn's rings are the most extensive ring system of any planet in the Solar System, and thus have been known to exist for quite some time. Galileo Galilei first observed them in 1610, but they were not accurately described as a disk around Saturn until Christiaan Huygens did so in 1655. The rings are not
Rings of Saturn - Misplaced Pages Continue
4116-427: The 19th century is that the rings were once a moon of Saturn (named Veritas, after a Roman goddess who hid in a well). According to the theory, the moon's orbit decayed until it was close enough to be ripped apart by tidal forces (see Roche limit ). Numerical simulations carried out in 2022 support this theory; the authors of that study proposed the name " Chrysalis " for the destroyed moon. A variation on this theory
4214-438: The A, B and C rings. It is a small fraction of the total mass of Saturn (about 0.25 ppb ). Earlier Voyager observations of density waves in the A and B rings and an optical depth profile had yielded a mass of about 0.75 Mimas masses, with later observations and computer modeling suggesting that was an underestimate. Although the largest gaps in the rings, such as the Cassini Division and Encke Gap , can be seen from Earth,
4312-420: The B Ring may be massive enough to have diluted infalling material and thus avoided substantial darkening over the age of the Solar System. Ring material may be recycled as clumps form within the rings and are then disrupted by impacts. This would explain the apparent youth of some of the material within the rings. Evidence suggesting a recent origin of the C ring has been gathered by researchers analyzing data from
4410-409: The B Ring's surface density is in the range of 40 to 140 g/cm, lower than previously believed, and that the ring's optical depth has little correlation with its mass density (a finding previously reported for the A and C rings). The total mass of the B Ring was estimated to be somewhere in the range of 7 to 24 × 10 kg. This compares to a mass for Mimas of 37.5 × 10 kg. Until 1980, the structure of
4508-416: The Cassini Division (discovered in 1675 by Giovanni Domenico Cassini ). Along with the C Ring, which was discovered in 1850 and is similar in character to the Cassini Division, these regions constitute the main rings . The main rings are denser and contain larger particles than the tenuous dusty rings . The latter include the D Ring, extending inward to Saturn's cloud tops, the G and E Rings and others beyond
4606-452: The Earth may have had a ring system during the mid-late Ordovician period. There are three ways that thicker planetary rings have been proposed to have formed: from material originating from the protoplanetary disk that was within the Roche limit of the planet and thus could not coalesce to form moons, from the debris of a moon that was disrupted by a large impact, or from the debris of
4704-454: The F ring). Other gaps arise from resonances between the orbital period of particles in the gap and that of a more massive moon further out; Mimas maintains the Cassini Division in this manner. Still more structure in the rings consists of spiral waves raised by the inner moons' periodic gravitational perturbations at less disruptive resonances. Data from the Cassini space probe indicate that
4802-417: The Solar System have rings, the existence of exoplanets with rings is plausible. Although particles of ice , the material that is predominant in the rings of Saturn , can only exist around planets beyond the frost line , within this line rings consisting of rocky material can be stable in the long term. Such ring systems can be detected for planets observed by the transit method by additional reduction of
4900-439: The Sun passes through the ring plane, are not evenly spaced. The sun passes south to north through the ring plane when Saturn's heliocentric longitude is 173.6 degrees (e.g. 11 August 2009), about the time Saturn crosses from Leo to Virgo. 15.7 years later Saturn's longitude reaches 353.6 degrees and the sun passes to the south side of the ring plane. On each orbit the Sun is north of the ring plane for 15.7 Earth years, then south of
4998-495: The disrupted icy mantle. This formation mechanism predicts that roughly 10% of centaurs will have experienced potentially ring-forming encounters with giant planets. The composition of planetary ring particles varies, ranging from silicates to icy dust. Larger rocks and boulders may also be present, and in 2007 tidal effects from eight moonlets only a few hundred meters across were detected within Saturn's rings. The maximum size of
SECTION 50
#17327720296845096-455: The faster this infall, the shorter the lifetime of the ring system. One mechanism involves gravity pulling electrically charged water ice grains down from the rings along planetary magnetic field lines, a process termed 'ring rain'. This flow rate was inferred to be 432–2870 kg/s using ground-based Keck telescope observations; as a consequence of this process alone, the rings will be gone in ~ 292 +818 −124 million years. While traversing
5194-433: The first trans-Neptunian object found to have a ring system. The ring has a radius of about 2,287 km , a width of ≈ 70 km and an opacity of 0.5. The ring plane coincides with Haumea's equator and the orbit of its larger, outer moon Hi’iaka (which has a semimajor axis of ≈ 25,657 km ). The ring is close to the 3:1 resonance with Haumea's rotation, which is located at a radius of 2,285 ± 8 km . It
5292-430: The gap between the C Ring and D73, the structure was found during Saturn's 2009 equinox to extend a radial distance of 19,000 km (12,000 miles) from the D Ring to the inner edge of the B Ring. The waves are interpreted as a spiral pattern of vertical corrugations of 2 to 20 m amplitude; the fact that the period of the waves is decreasing over time (from 60 km; 40 miles in 1995 to 30 km; 20 miles by 2006) allows
5390-488: The gap between the rings and planet in September 2017, the Cassini spacecraft detected an equatorial flow of charge-neutral material from the rings to the planet of 4,800–44,000 kg/s. Assuming this influx rate is stable, adding it to the continuous 'ring rain' process implies the rings may be gone in under 100 million years. The densest parts of the Saturnian ring system are the A and B Rings, which are separated by
5488-403: The inner or outer edges of a ringlet or within gaps in the rings. The gravity of shepherd moons serves to maintain a sharply defined edge to the ring; material that drifts closer to the shepherd moon's orbit is either deflected back into the body of the ring, ejected from the system, or accreted onto the moon itself. It is also predicted that Phobos , a moon of Mars, will break up and form into
5586-406: The last 100 million years, and may thus be between 10 million and 100 million years old. This recent origin scenario is based on a new, low mass estimate modeling of the rings' dynamical evolution, and measurements of the flux of interplanetary dust, which feed into an estimate of the rate of ring darkening over time. Since the rings are continually losing material, they would have been more massive in
5684-425: The light of the central star if their opacity is sufficient. As of 2024, two candidate extrasolar ring systems have been found by this method, around HIP 41378 f and K2-33b . Fomalhaut b was found to be large and unclearly defined when detected in 2008. This was hypothesized to either be due to a cloud of dust attracted from the dust disc of the star, or a possible ring system, though in 2020 Fomalhaut b itself
5782-483: The long-term variation in Chiron's brightness over time. Chiron's rings are suspected to be maintained by orbiting material ejected during seasonal outbursts, as a third partial ring detected in 2018 had become a full ring by 2022, with an outburst in between in 2021. A ring around Haumea , a dwarf planet and resonant Kuiper belt member , was revealed by a stellar occultation observed on 21 January 2017. This makes it
5880-475: The low-density regions of Saturn's rings. However, they are faint and dusty, much more similar in structure to those of Jupiter. The very dark material that makes up the rings is likely organics processed by radiation , like in the rings of Uranus. 20 to 70 percent of the rings are dust , a relatively high proportion. Hints of the rings were seen for decades prior to their conclusive discovery by Voyager 2 in 1989. A 2024 study suggests that Earth may have had
5978-406: The main ring system. These diffuse rings are characterised as "dusty" because of the small size of their particles (often about a μm ); their chemical composition is, like the main rings, almost entirely water ice. The narrow F Ring, just off the outer edge of the A Ring, is more difficult to categorize; parts of it are very dense, but it also contains a great deal of dust-size particles. The D Ring
SECTION 60
#17327720296846076-554: The nearby 2:1 resonance with Mimas and the influence of the eccentric outer edge of the B-ring. There is an additional narrow ringlet just outside the Huygens Ringlet. The A Ring is the outermost of the large, bright rings. Its inner boundary is the Cassini Division and its sharp outer boundary is close to the orbit of the small moon Atlas . The A Ring is interrupted at a location 22% of the ring width from its outer edge by
6174-437: The northern and southern ends of Brazil. A second centaur, 2060 Chiron , has a constantly evolving disk of rings. Based on stellar-occultation data that were initially interpreted as resulting from jets associated with Chiron's comet-like activity, the rings are proposed to be 324 ± 10 km in radius, though their evolution does change the radius somewhat. Their changing appearance at different viewing angles can explain
6272-406: The outer edge of the B Ring contains vertical structures deviating up to 2.5 km (1½ miles) from the main ring plane, a significant deviation from the vertical thickness of the main A, B and C rings, which is generally only about 10 meters (about 30 feet). Vertical structures can be created by unseen embedded moonlets. A 2016 study of spiral density waves using stellar occultations indicated that
6370-550: The outer part of the C Ring. It also contains a dense non-circular ringlet, the Maxwell Ringlet. In many respects this ringlet is similar to the ε ring of Uranus . There are wave-like structures in the middle of both rings. While the wave in the ε ring is thought to be caused by Uranian moon Cordelia , no moon has been discovered in the Maxwell gap as of July 2008. The B Ring is the largest, brightest, and most massive of
6468-405: The past than at present. The mass estimate alone is not very diagnostic, since high mass rings that formed early in the Solar System's history would have evolved by now to a mass close to that measured. Based on current depletion rates, they may disappear in 300 million years. There are two main theories regarding the origin of Saturn's inner rings. A theory originally proposed by Édouard Roche in
6566-496: The plane for 13.7 years. Dates for north-to-south crossings include 19 November 1995 and 6 May 2025, with south-to-north crossings on 11 August 2009 and 23 January 2039. During the period around an equinox the illumination of most of the rings is greatly reduced, making possible unique observations highlighting features that depart from the ring plane. The dense main rings extend from 7,000 km (4,300 mi) to 80,000 km (50,000 mi) away from Saturn's equator, whose radius
6664-487: The planet Saturn from around 1652 with the aim of explaining its appearance. His hypothesis was written up in De corpore saturni, in which he came close to suggesting the planet had a ring. However, Wren was unsure whether the ring was independent of the planet, or physically attached to it. Before Wren's hypothesis was published Christiaan Huygens presented his hypothesis of the rings of Saturn. Immediately Wren recognised this as
6762-399: The planet or, in the case of Saturn's E-ring, the ejecta of cryovolcanic material. Ring systems may form around centaurs when they are tidally disrupted in a close encounter (within 0.4 to 0.8 times the Roche limit ) with a giant planet. For a differentiated body approaching a giant planet at an initial relative velocity of 3−6 km/s with an initial rotational period of 8 hours,
6860-504: The planet, C, B and A, with the Cassini Division, the largest gap, separating Rings B and A. Several fainter rings were discovered more recently. The D Ring is exceedingly faint and closest to the planet. The narrow F Ring is just outside the A Ring. Beyond that are two far fainter rings named G and E. The rings show a tremendous amount of structure on all scales, some related to perturbations by Saturn's moons, but much unexplained. In September 2023, astronomers reported studies suggesting that
6958-481: The planet], inclined to the ecliptic"). He published his ring hypothesis in Systema Saturnium (1659) which also included his discovery of Saturn's moon, Titan , as well as the first clear outline of the dimensions of the Solar System . In 1675, Giovanni Domenico Cassini determined that Saturn's ring was composed of multiple smaller rings with gaps between them; the largest of these gaps was later named
7056-649: The planned resolution; nevertheless, images from the spacecraft provided unprecedented detail of the ring system and revealed the existence of the G ring. Voyager 2 ' s closest approach occurred in August 1981 at a distance of 41,000 km (25,000 mi). Voyager 2 ' s working photopolarimeter allowed it to observe the ring system at higher resolution than Voyager 1 , and to thereby discover many previously unseen ringlets. Cassini spacecraft entered into orbit around Saturn in July 2004. Cassini 's images of
7154-414: The ring is blocked, so that when seen from above, the ring is close to transparent. The 30-km wavelength spiral corrugations first seen in the D Ring were observed during Saturn's equinox of 2009 to extend throughout the C Ring (see above). The Colombo Gap lies in the inner C Ring. Within the gap lies the bright but narrow Colombo Ringlet, centered at 77,883 km (48,394 miles) from Saturn's center, which
7252-546: The ring must be composed of numerous small particles, all independently orbiting Saturn. Later, Sofia Kovalevskaya also found that Saturn's rings cannot be liquid ring-shaped bodies. Spectroscopic studies of the rings which were carried out independently in 1895 by James Keeler of the Allegheny Observatory and by Aristarkh Belopolsky of the Pulkovo Observatory showed that Maxwell's analysis
7350-458: The ring system via their gravitational effect during its final set of orbits that passed between the rings and the cloud tops, yielding a value of 1.54 (± 0.49) × 10 kg, or 0.41 ± 0.13 Mimas masses. This is around two-thirds the mass of the Earth's entire Antarctic ice sheet , spread across a surface area 80 times larger than that of Earth. The estimate is close to the value of 0.40 Mimas masses derived from Cassini observations of density waves in
7448-488: The rings and they became invisible. Mystified, Galileo remarked "I do not know what to say in a case so surprising, so unlooked for and so novel." He mused, "Has Saturn swallowed his children?" — referring to the myth of the Titan Saturn devouring his offspring to forestall the prophecy of them overthrowing him. He was further confused when the rings again became visible in 1613. Early astronomers used anagrams as
7546-485: The rings are the most detailed to-date, and are responsible for the discovery of yet more ringlets. The rings are named alphabetically in the order they were discovered: A and B in 1675 by Giovanni Domenico Cassini , C in 1850 by William Cranch Bond and his son George Phillips Bond , D in 1933 by Nikolai P. Barabachov and B. Semejkin , E in 1967 by Walter A. Feibelman , F in 1979 by Pioneer 11 , and G in 1980 by Voyager 1 . The main rings are, working outward from
7644-520: The rings extend significantly out of the nominal ring plane in a few places. This displacement reaches as much as 4 km (2.5 mi) at the border of the Keeler Gap , due to the out-of-plane orbit of Daphnis , the moon that creates the gap. Estimates of the age of Saturn's rings vary widely, depending on the approach used. They have been considered to possibly be very old, dating to the formation of Saturn itself. However, data from Cassini suggest they are much younger, having most likely formed within
7742-421: The rings of Saturn may have resulted from the collision of two moons "a few hundred million years ago". Saturn's axial tilt is 26.7°, meaning that widely varying views of the rings, of which the visible ones occupy its equatorial plane, are obtained from Earth at different times. Earth makes passes through the ring plane every 13 to 15 years, about every half Saturn year, and there are about equal chances of either
7840-419: The rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular oxygen gas (O 2 ) produced when ultraviolet light from the Sun interacts with water ice in the rings. Chemical reactions between water molecule fragments and further ultraviolet stimulation create and eject, among other things, O 2 . According to models of this atmosphere, H 2
7938-581: The rings of Saturn was explained as being caused exclusively by the action of gravitational forces. Then images from the Voyager spacecraft showed radial features in the B Ring , known as spokes , which could not be explained in this manner, as their persistence and rotation around the rings was not consistent with gravitational orbital mechanics . The spokes appear dark in backscattered light, and bright in forward-scattered light (see images in Gallery );
8036-494: The rings were likely to have formed early in the Solar System's history, newer data from Cassini suggested they formed relatively late. Although reflection from the rings increases Saturn's brightness , they are not visible from Earth with unaided vision . In 1610, the year after Galileo Galilei turned a telescope to the sky, he became the first person to observe Saturn's rings, though he could not see them well enough to discern their true nature. In 1655, Christiaan Huygens
8134-472: The rings, due to gravitational interactions with the rings and tidal interaction with Saturn, into progressively wider orbits. Within the Roche limit , bodies of rocky material are dense enough to accrete additional material, whereas less-dense bodies of ice are not. Once outside the rings, the newly formed moons could have continued to evolve through random mergers. This process may explain the variation in silicate content of Saturn's moons out to Rhea, as well as
8232-468: The rings. Alternatively, it is proposed that the spokes are very similar to a phenomenon known as lunar horizon glow or dust levitation, and caused by intense electric fields across the terminator of ring particles, not electrical disturbances. The spokes were not observed again until some twenty-five years later, this time by the Cassini space probe. The spokes were not visible when Cassini arrived at Saturn in early 2004. Some scientists speculated that
8330-409: The rings. Its thickness is estimated as 5 to 15 m and its optical depth varies from 0.4 to greater than 5, meaning that >99% of the light passing through some parts of the B Ring is blocked. The B Ring contains a great deal of variation in its density and brightness, nearly all of it unexplained. These are concentric, appearing as narrow ringlets, though the B Ring does not contain any gaps. In places,
8428-502: The same physics that describes the spiral arms of galaxies . Spiral bending waves, also present in the A Ring and also described by the same theory, are vertical corrugations in the ring rather than compression waves. Ring system Ring systems are best known as planetary rings, common components of satellite systems around giant planets such as of Saturn , or circumplanetary disks . But they can also be galactic rings and circumstellar discs , belts of planetoids, such as
8526-457: The southern. In 1980, Voyager 1 made a fly-by of Saturn that showed the F ring to be composed of three narrow rings that appeared to be braided in a complex structure; it is now known that the outer two rings consist of knobs, kinks and lumps that give the illusion of braiding, with the less bright third ring lying inside them. New images of the rings taken around the 11 August 2009 equinox of Saturn by NASA's Cassini spacecraft have shown that
8624-467: The spokes may be a seasonal effect, varying with Saturn's 29.7-year orbit, were supported by their gradual reappearance in the later years of the Cassini mission. In 2009, during equinox, a moonlet embedded in the B ring was discovered from the shadow it cast. It is estimated to be 400 m (1,300 ft) in diameter. The moonlet was given the provisional designation S/2009 S 1 . The Cassini Division
8722-430: The spokes would not be visible again until 2007, based on models attempting to describe their formation. Nevertheless, the Cassini imaging team kept looking for spokes in images of the rings, and they were next seen in images taken on 5 September 2005. The spokes appear to be a seasonal phenomenon, disappearing in the Saturnian midwinter and midsummer and reappearing as Saturn comes closer to equinox . Suggestions that
8820-499: The star UCAC4 248-108672 on June 3, 2013 from seven locations in South America. While watching, they saw two dips in the star's apparent brightness just before and after the occultation. Because this event was observed at multiple locations, the conclusion that the dip in brightness was in fact due to rings is unanimously the leading hypothesis. The observations revealed what is likely a 19-kilometer (12-mile)-wide ring system that
8918-576: The time between then and 2005, observations by Voyager 2 and the Hubble Space Telescope led to a total of 13 distinct rings being identified, most of which are opaque and only a few kilometers wide. They are dark and likely consist of water ice and some radiation-processed organics . The relative lack of dust is due to aerodynamic drag from the extended exosphere - corona of Uranus. The system around Neptune consists of five principal rings that, at their densest, are comparable to
9016-513: The transition occurs at a phase angle near 60 ° . The leading theory regarding the spokes' composition is that they consist of microscopic dust particles suspended away from the main ring by electrostatic repulsion, as they rotate almost synchronously with the magnetosphere of Saturn. The precise mechanism generating the spokes is still unknown. It has been suggested that the electrical disturbances might be caused by either lightning bolts in Saturn's atmosphere or micrometeoroid impacts on
9114-444: The trend towards less silicate content closer to Saturn. Rhea would then be the oldest of the moons formed from the primordial rings, with moons closer to Saturn being progressively younger. The brightness and purity of the water ice in Saturn's rings have also been cited as evidence that the rings are much younger than Saturn, as the infall of meteoric dust would have led to a darkening of the rings. However, new research indicates that
9212-541: Was correct. Four robotic spacecraft have observed Saturn's rings from the vicinity of the planet. Pioneer 11 ' s closest approach to Saturn occurred in September 1979 at a distance of 20,900 km (13,000 mi). Pioneer 11 was responsible for the discovery of the F ring. Voyager 1 ' s closest approach occurred in November 1980 at a distance of 64,200 km (39,900 mi). A failed photopolarimeter prevented Voyager 1 from observing Saturn's rings at
9310-481: Was detected from Earth by the Hubble Space Telescope. Saturn shows complex patterns in its brightness. Most of the variability is due to the changing aspect of the rings, and this goes through two cycles every orbit. However, superimposed on this is variability due to the eccentricity of the planet's orbit that causes the planet to display brighter oppositions in the northern hemisphere than it does in
9408-405: Was determined to very likely be an expanding debris cloud from a collision of asteroids rather than a planet. Similarly, Proxima Centauri c has been observed to be far brighter than expected for its low mass of 7 Earth masses, which may be attributed to a ring system of about 5 R J . A 56-day-long sequence of dimming events in the star V1400 Centauri observed in 2007 was interpreted as
9506-403: Was surrounded by a ring detached from the planet, and famously published the letter string " aaaaaaacccccdeeeeeghiiiiiiillllmmnnnnnnnnnooooppqrrstttttuuuuu ". Three years later, he revealed it to mean Annulo cingitur, tenui, plano, nusquam coherente, ad eclipticam inclinato ("[Saturn] is surrounded by a thin, flat, ring, nowhere touching [the body of
9604-609: Was the first person to describe them as a disk surrounding Saturn. The concept that Saturn's rings are made up of a series of tiny ringlets can be traced to Pierre-Simon Laplace , although true gaps are few – it is more correct to think of the rings as an annular disk with concentric local maxima and minima in density and brightness. On the scale of the clumps within the rings there is much empty space. The rings have numerous gaps where particle density drops sharply: two opened by known moons embedded within them, and many others at locations of known destabilizing orbital resonances with
#683316