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Why Only Saturn Has Visible Rings

Why Only Saturn Has Visible Rings


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It may be surprising to know that all four giants in our solar system have rings orbiting around them. Yet only Saturn has a system of rings visible to the naked eye. Why is that? What's so different about Saturn in comparison to Jupiter, Uranus and Neptune that makes it the only planet to have a visible ring system?


By "visible to the naked eye", I take it you mean "visible from Earth with a small telescope".

Saturn's rings are largely water ice, and so they reflect more sunlight back to us.

Jupiter's rings, have lower proportions of ice, and lots of smaller dust particles that tend to scatter light forward rather than back to us.

The ring systems of Uranus and Neptune are made of really dark material, so also don't reflect much light in our direction.


Building on what hartacus said, there's a couple other reasons involved as well:

Uranus and Neptune are much further out:

At closest approach to earth the distance to:

  • Saturn is about 746 million miles (1.2 billion km)
  • Uranus is about 1.7 billion miles (2.5 billion km)
  • Neptune is about 2.7 billion miles (4.3 billion km)

So Uranus and Neptune are very far away… and they're also smaller, AND their rings are not as dense.

In an amateur telescope, it's very hard to see Uranus as anything other than a small, dim, fuzzy, blueish disk. Neptune is just a blue-green dot. The rings are so insubstantial, in comparison, that they just don't stand out.

In the case of Jupiter, the problem is simply that they're so insubstantial. The Jovian rings are very thin when compared to Saturn's. Two flyby missions, Pioneer 10 and Pioneer 11, flew by Jupiter without noticing them at all.

Combined with the difference in composition and albedo, they're just not visible to smaller Earth-based telescopes.


Why Only Saturn Has Visible Rings - Astronomy


A more detailed view of the inner brighter rings, comparing visual and radio observations
Click here for a much more detailed view NASA, JPL, Planetary Photojournal)

A view of Saturn and its rings from above, showing the shadow of the planet on the rings. The sunward (daylit) part of the planet is overexposed, so that the partial lighting of the night side caused by reflection from the rings is visible. (This image is a composite of several Cassini spacecraft images, so artifacts caused by combining the images are also visible, particularly on the night side.) (Cassini Imaging Team, SSI, JPL, ESA, NASA, apod070306) An additional ring was recently discovered in the orbit of Phoebe, which see for a discussion of the new ring.

The Appearance of the Rings
The rings of Saturn consist of a sheet-like distribution of icy particles, most about the size and composition of snowballs, orbiting Saturn in individual almost exactly circular orbits, at various distances from the planet. All of the particles are well inside a region defined by the Roche Limit, within which the gravity of Saturn tends to tear apart large objects. They are continually colliding with each other and building up to larger sizes, and at the same time continually breaking down through collisions and their gravitational interaction with Saturn, so that the distribution of particle sizes is roughly constant over time.
The rings are over 120,000 miles in diameter but are very thin, being no more than a few hundred yards thick at any given place, although bending waves caused by the interaction of the ring particles with each other and various moons cause the "surface" of the rings to fluctuate up and down by several times that distance. As a result, when the rings are viewed "edge-on" they can essentially disappear from view. How this works is shown in the diagram below:


How Saturn's rings are oriented at various points in its orbit.
(Modified from Chaisson, "Astronomy Today")




Saturn's rings near its equinox, nearly edge-on to the Sun and therefore unlit
(Cassini Imaging Team, ISS, JPL, ESA, NASA, apod090825)


Saturn's shadow and rings close to its equinox
(Cassini Imaging Team, ISS, JPL, ESA, NASA, apod090901)




When the Cassini spacecraft arrived at Saturn, no spokes were visible in its rings, leaving various controversies about the spokes' nature and origins unsettled. Recently, however, spokes have been seen, as in the above image, taken from the shadow side of the rings, so that the spokes are viewed as light against the darker background of the rings. It is hoped that further study of the spokes may finally reveal their origin, and more certainly establish their physical nature and the forces controlling their behavior. (CICLOPS, JPL, ESA, NASA apod061127)

Why Are The Rings So Flat?
As noted above the rings of Saturn are incredibly flat -- in most places only a few hundred yards thick, compared to more than a hundred thousand miles breadth. For this to occur the particles that make up the rings -- countless numbers of icy bodies of various sizes -- must all have very nearly the same velocity as they orbit the planet. Any difference in their motion, whether radial (in or out relative to a perfectly circular orbit), tangential (faster or slower relative to the circular orbital velocity in their vicinity), or vertical (up or down relative to the plane of the rings), must be less than a hundred thousandth of a percent of their average velocity. In other words, although orbiting Saturn at a hundred thousand miles an hour, their relative velocities in a given region must be only 50 feet per hour.
The reason for this can be seen by imagining what would happen if there were particles which had a substantial vertical motion relative to the rest of the ring particles. Such objects would have orbits which move upwards on one side of the orbit and downwards on the other side, and on opposite sides of the planet, pass through the ring plane. If there were very little material in the way they might be able to do this indefinitely, and if this were possible undoubtedly many objects would do so, if only as a result of collisions with other objects, and the rings would be much thicker. But instead, since there is so much material in the rings that in many places they can block the light of distant stars, the odds are that any particles with significant vertical motions would collide with particles in the ring plane almost every time they had to pass through it. And in those collisions, their vertical motion would be "damped out" by being shared with the objects they collided with, and the objects those objects collided with and so on.
A similar thing would happen if there were significant radial or tangential variations in velocity, so in any given region all differential motions must be as small as the thickness of the rings is compared to their breadth.

Saturn's Influence Within the Rings
Although the differential motions inside the rings must be small, there must be occasional collisions between ring particles. Given the slow speeds with which they move relative to and therefore strike each other, it is more likely that such collisions will build larger and larger objects (this growth through collision is referred to as accretion), even if the objects are made of relatively loose, fragile structures, as many of the icy bodies in the outer Solar System appear to be. In fact it has been estimated that most of the material within a given part of the rings might well combine to form small moonlets a few miles in diameter within periods of a few weeks or months. There is, however, a problem with this -- namely, the immense mass of Saturn, and its correspondingly immense gravity.
The main effect of Saturn's gravity is of course to keep the ring particles in orbit around it but just as the Moon raises tides on the Earth (and the Earth on the Moon, albeit "frozen" tides in that case), Saturn can raise tides within the larger bodies surrounding it. For very small objects the difference in gravity due to Saturn on the side of the object closer to Saturn and on the side of the object further from Saturn is insignificant, even in comparison with the weak forces which hold the icy bodies together, simply because of their "stickiness". But if they were to grow to several miles diameter the tidal forces would become much larger and in fact any object within a certain distance of Saturn -- referred to as the Roche Limit after its discoverer -- would be stretched by tidal forces from the planet greater than any gravitational attraction it exerts on itself, and as soon as it was large enough, further collisions would tend to shatter it into smaller pieces, rather than build it up to larger size.
As it happens, virtually all of the ring material lies well within the Roche Limit for Saturn, so although collisions tend to build things up on short time scales, eventually the larger objects tend to break down into smaller pieces, and on the average the distribution of ring particle sizes must be roughly constant. There is, however, another factor, which promises to end the existence of the rings as we know them within a few tens or hundreds of millions of years. That factor is the outer atmosphere of Saturn, which although incredibly rarefied at the distance from Saturn of its rings, can exert very small frictional forces on the ring particles, particularly in the inner parts of the rings. As a result, there is a slow infall of material toward the planet, which over very long times will remove most of the material from the rings and erase their spectacular appearance. This implies that the rings must not be a permanent feature, but were probably formed by the passage of a comet or some other icy body too close to Saturn to remain in one piece in the not too distant past "not too distant" in this case meaning sometime within the last few hundreds of millions of years.

The Influence of Saturn's Moons Within the Rings
Some of the moons of Saturn can also exert gravitational forces on the rings. The most significant of these is Mimas, which is directly responsible for the Cassini Division -- the large, dark, nearly empty area which divides the outer rings from the inner rings. The Division is caused by a resonance between the orbital period of ring particles that are in that region with the orbital period of Mimas. (For now, see Mimas for a discussion of this interaction.)

A Comparison of the Rings of Saturn to the Solar Nebula
A similar thing would have happened in the early Solar System, as we will see when discussing the origin of the Solar System. At that time the now solid portions of the planets would have existed as gases, or as innumerable bits of microscopic dust -- ices, soots and metal oxides -- orbiting the Sun, within the Solar Nebula. With such huge amounts of gas and dust interactions between the materials in a given region would guarantee that the motions were nearly uniform, and collisional velocities would be very small, allowing things to build up very rapidly. A similar thing occurs in the rings of Saturn, but because of the close proximity of Saturn (all of the rings are within a region defined by the Roche Limit, where Saturn's gravity is stronger than the gravity of the ring particles), objects that build up to large sizes are more likely to be torn apart than to grow still further. In the Solar Nebula, the Roche Limit for the Sun was in a region where no solid materials could exist because of the Sun's high temperature, so it was not a factor and as objects rapidly built up through collisions there was no limit on how large they could grow, save for the amount of available materials.

Some (older) detailed images of the rings, showing density and radial waves

Above, an overall image (namely, the visible-light image near the top of this page)
Below, larger views of portions of the rings


Saturn’s clouds run deep, rings may rain organics

Artist’s illustration of Saturn’s internal structure. Credit: NASA/JPL-Caltech

Saturn’s clouds have roots deeper inside the planet’s atmosphere than scientists previously thought, and Saturn’s rings — now believed to have formed in the last 200 million years — appear to be raining organic molecules down on the planet, according to observations made by NASA’s Cassini spacecraft last year in the final weeks of its mission.

The discoveries from Cassini’s grand finale, when the long-lived plutonium-powered space probe passed through a gap between Saturn and its rings, continue to keep scientists on their toes.

“The weather and what you’re seeing on Saturn is not just in the very thin atmosphere that you’re seeing, it’s deeper,” said Linda Spilker, the Cassini project scientist at NASA’s Jet Propulsion Laboratory.

During Cassini’s 22 passages inside Saturn’s rings, the spacecraft measured the gas giant’s gravity directly, allowing scientists to differentiate effects from the rings and the planet itself. Running low on fuel, Cassini plunged into Saturn’s atmosphere Sept. 15, 2017, as intended.

The measurements gave Cassini scientists a better idea of Saturn’s internal structure, showing how mass is distributed inside the planet. The data also help scientists improve calculations of the mass of Saturn’s rings, a figure that yields an estimate of their age.

Weather systems on Saturn are not as visually spectacular as those on Jupiter, but Spilker said scientists now see evidence that Saturn’s clouds and jet streams extend much deeper into the planet than they expected.

“The initial thought was that thickness was maybe only a few hundreds of kilometers, or something like that, and it’s turning out to be thousands of kilometers instead,” Spilker said last month at the 49th Lunar and Planetary Science Conference near Houston.

NASA’s Juno spacecraft, currently exploring the internal structure of Jupiter, has found that planet’s jet streams also extend well beneath the cloud tops, perhaps to a depth of 1,900 miles (3,000 kilometers).

The Juno team made that announcement in early March.

“Galileo viewed the stripes on Jupiter more than 400 years ago,” said Yohai Kaspi, Juno co-investigator from the Weizmann Institute of Science in Rehovot, Israel, and lead author of a Nature paper on Jupiter’s deep weather layer. “Until now, we only had a superficial understanding of them and have been able to relate these stripes to cloud features along Jupiter’s jets. Now, following the Juno gravity measurements, we know how deep the jets extend and what their structure is beneath the visible clouds. It’s like going from a 2-D picture to a 3-D version in high definition.”

In a stroke of fortune for planetary scientists, Cassini made similar measurements of Saturn’s deep interior at the same time as Juno was probing Jupiter.

“At Jupiter, they saw the atmospheric depth of 3,000 kilometers,” Spilker said. “That was pretty amazing, and now Saturn is much deeper. It will be interesting to see when they start comparing Jupiter and Saturn.”

Artist’s illustration of the Cassini spacecraft during one of its final orbits between Saturn and its rings. Credit: NASA/JPL-Caltech

Gravity data from Cassini’s final 22 orbits also point to a relatively recent formation of Saturn’s rings — some time in the last 200 million years, about the time dinosaurs began to flourish on Earth, and a fraction of the roughly 4.5 billion-year age of Saturn itself. The prevailing theory is that a comet, a moon, or some other cosmic interloper ventured too close Saturn. Saturn’s gravity ripped the object apart, and the leftover ice and dust formed the planet’s famous rings.

Scientists derived Saturn’s ring age from the rings’ mass.

“Prior to the grand finale orbits, that mass was uncertain by about 100 percent, which is a lot,” Spilker said.

There is still some uncertainty in the ring mass estimate after Cassini, but the error bars have narrowed, and the estimate centers on a number slightly less massive than earlier predictions.

Spilker said the results have been submitted for publication in Science magazine.

“This points to very young rings, rings that are probably on the order of 100 million years old or so, because of this very low mass for the rings,” Spilker said. “So this was really an astonishing result, a new result that we could get with Cassini.”

Jeff Cuzzi, an expert on Saturn’s rings at NASA’s Ames Research Center, said it is time for scientists to rethink their theories on how the rings formed.

The biggest objects in the solar system had settled into stable orbits around the sun by the time the rings appeared at Saturn, Cuzzi said, making the probability of a large chunk of rock or ice venturing close to the planet 200 million years ago “statistically unlikely.”

He said a moon the size of Titan, which is 50 percent larger than Earth’s moon, could have drifted too close to Saturn and been ripped apart. But that scenario was also much more likely to happen when the solar system was more chaotic billions of years ago.

“The only young scenario that has any plausibility … is whereby the Saturn moon system might have ben evolving very stably over almost the whole age of the solar system until a resonance was hit about 100 million years ago,” Cuzzi said.

The moons’ orbits would have become unstable in such a scenario, Cuzzi said, causing them to collide with one another and shed icy debris.

Scientists still have to resolve some lingering questions in such a scenario, such as how the debris could have migrated to the rings’ current positions, Cuzzi said. Research has shown that a recent resonance between moons could have only occurred at Saturn, and that may be why fresh, bright rings are seen there but not around other planets in the solar system.

“All of the giant planets have these little wimpy rings of dark primordial material,” Cuzzi said. “Only Saturn has these massive icy rings.”

“They’re not going to go away, they’re just going to keep getting darker,” Cuzzi said. “We’re just lucky to see them now.”

Cassini also made the first direct measurement of material raining down on Saturn from the planet’s innermost ring.

Several of Cassini’s instruments detected microscopic particles, most of which were smaller than a thousandth of a millimeter in size, as the probe dove between the visible rings and Saturn’s cloud tops. Previous studies suggested the rings may deposit material into Saturn’s atmosphere.

File photo of a backlit Saturn and its rings taken by the Cassini spacecraft in 2006. Credit: NASA/JPL-Caltech

The particles — or “nano-grains” as some scientists call them — were too small to pose a hazard to Cassini as the spacecraft flew through the ring gap at more than 60,000 mph.

The material rains down on Saturn’s atmosphere near the planet’s equator. Scientists have identified much of the material as water ice — no surprise because water makes up more than 90 percent of the rings.

But initial results show there are heavier particles, including organic molecules like methane, embedded in the material raining down from the D ring. And the ratio of water ice in the “ring rain” is lower than the percentage of water in the rings themselves, suggesting the water has been lost.

That discovery was unexpected.

Researchers are now on the hunt for the source of the carbon-bearing organic molecules. They could be brought in from external sources, such as Saturn’s moons or comets, scientists said.

Saturn’s rings have a muted reddish hue when analysts exaggerate their color in imagery.

“Are they red because of good, old-fashioned rust like Mars, or are they red because of the same kinds of organic materials … that make carrots, tomatoes and watermelon red?” Cuzzi said.

“To me, this answers the question of what makes the rings red. It’s organics.”

Follow Stephen Clark on Twitter: @StephenClark1.


Worlds of Creation: Saturn

Known for its stunning system of rings, Saturn is truly a gem of the solar system. Although Jupiter, Uranus, and Neptune also have rings, only Saturn’s are easily visible from Earth and are an icon of astronomy. Yet these rings were unknown until the 1600s. For the first five and a half millennia, Saturn was simply the slowest of the five “wandering stars.” The invention of the telescope in 1608 paved the way for more advanced telescopes, eventually allowing astronomers to see Saturn in all its splendor.

Orbital Properties and Physical Characteristics

Saturn orbits the sun at an average distance of 890 million miles, which is nine and a half times the radius of Earth’s orbit. The sun would therefore appear nearly ten times smaller as seen from Saturn, and would be 92 times fainter. With so little solar energy, Saturn maintains a rather chilly temperature of 218 degrees below zero on the Fahrenheit scale.[1] Saturn takes 29.5 years to orbit the sun once. But it has the second fastest rotation of any planet: about 10.5 hours.

Saturn is a Jovian planet – meaning “like Jupiter.” It is a gas giant, with no solid surface, consisting almost entirely of hydrogen and helium gas with trace elements that form compounds like ammonia and methane. These trace compounds give rise to the subtle colors in the atmosphere of Saturn. Saturn’s clouds are stretched into belts and zones, much like on Jupiter. But Saturn’s belts and zones are far less distinctive in appearance than those of Jupiter. Saturn’s rapid rotation causes the shape of the planet to be an oblate spheroid, with an equatorial radius that is noticeably larger than its polar radius – just like Jupiter.

Saturn is about nine Earths in diameter, just a bit smaller than Jupiter, though considerably less massive. Saturn has the lowest density of any planet in the solar system. The average density of Saturn is only 0.687 grams per cubic centimeter, which is less than that of water. Hence, unlike any other planet, Saturn would float in water.

Saturn’s rotation axis is tilted nearly 27 degrees relative to its orbital axis, a bit more than Earth’s 23.5-degree tilt. Hence, Saturn experiences seasons like Earth, but nearly 30 times longer due to Saturn’s lengthy orbital period. Such a tilt is problematic from a secular perspective. In the standard secular formation scenario, the planets are said to have formed from a collapsing proto-solar nebula. In such a case, they all should be spinning about the same axis as their orbit due to conservation of angular momentum. But many do not. The Earth’s axial tilt is sometimes explained as the result of a large impact (for which there is no evidence). But this explanation won’t work for a large gas giant like Saturn. Instead, its tilt is a design feature, as we will explore below.

Saturn often develops storms in its atmosphere, which appear as either black or white features. It lacks a permanent storm like Jupiter’s Great Red Spot. However, a large white storm often appears in Saturn’s northern hemisphere during (Saturn’s) summer, which happens every thirty years. This storm was seen in 1990 and the next one was expected to appear in 2020. However, an enormous white storm appeared in 2010 – ten years early, much to the delight of astronomers. Fortunately, the Cassini spacecraft was orbiting Saturn at that time, and provided spectacular images of the event.

Cassini spacecraft image of Saturn showing a white storm in the northern hemisphere.
February 25, 2011

Like Jupiter, Saturn possesses significant internal heat. It radiates over 2.5 times as much energy as it receives from the sun. Since Saturn lacks any substantial radioactive elements to produce such heat, the most plausible explanation is that such heat is primordial – that is, God initially created Saturn with internal heat. But, if Saturn were billions of years old as secularists claim, then it should have radiated away all its heat long ago. Internal heat is generally indicative of recent creation.

Likewise, Saturn has a powerful magnetic field, though not as powerful as Jupiter’s field. Magnetic fields are caused by the movement of charged particles – electrical current. Since such current naturally decays over time, Saturn’s magnetic field is an indication that the planet is only thousands of years old, and nowhere near the secular assumed age. Saturn’s magnetic field often produces aurora near its poles.

Four spacecraft have visited Saturn. Pioneer 11 was the first to fly by Saturn in September, 1979. Voyager 1 visited Saturn in 1980, providing high-resolution images of the planet, its rings, and some of its moons. In particular, it made a close pass to Saturn’s largest moon: Titan. Voyager 2 passed Saturn in 1981, confirming the discovery of several new moons. The Cassini spacecraft was placed into orbit around Saturn in 2004, producing high-resolution images and collecting other data until the end of its mission in 2017.

Lord of the Rings

The most iconic feature of Saturn belongs not to the planet itself, but its system of rings. Galileo observed Saturn in his homemade telescope in the year 1610. He could see that Saturn appeared abnormally shaped. It was not a simple sphere, but had noticeable features on its left and right sides. However, his telescope was insufficient to discern what these features were. He thought perhaps he was seeing two moons to the left and right of Saturn. But why did they fail to orbit Saturn? The nature of Saturn’s odd appearance was perhaps the central problem in astronomy in the early to mid-1600s. The solution came in 1655, when Christiaan Huygens was able to discern that Saturn was encircled by a flat disk of rings.

Initially, most astronomers believed that the rings were a single solid disk. But we now understand that Saturn’s rings are composed of trillions of tiny moonlets made mostly of water ice that orbit around Saturn’s equator. These range in size from particles of dust, to larger pebbles, and perhaps some accretions that are several feet across. The main (easily visible) rings extend from 4,300 miles to 50,000 miles away from Saturn’s equator. For comparison, the (equatorial) radius of Saturn is 37,500 miles. The rings orbit in the plane of Saturn’s equator, and are less than one mile thick. For this reason, they cannot be seen when viewed edge-on.

The main rings are divided into three visibly distinct systems, called the A, B, and C rings. The A ring is the outermost, and is physically separated from the B ring by a noticeable break called the Cassini division. The Cassini division is often visible in a moderate backyard telescope under good seeing conditions. This thin break is, in reality, 2,920 miles wide! Although not completely empty, the Cassini division has far fewer particles than the main rings, and therefore appears dark.

The B ring is the brightest, and along with the A ring is easily visible in even a modest backyard telescope. In the 1980s, images from the Voyager missions revealed the existence of “spokes” within the B ring. These appeared as radial lines extending away from Saturn like the spokes of a bicycle wheel. Strangely, these spokes even appeared to exhibit solid-body rotation. That is, they do not move with the particles (which rotate differentially in accordance with Kepler’s third law), but all rotate with the same angular velocity as if they were on a solid disk. There are several hypotheses to explain these spokes, but there is currently no consensus explanation.

This Cassini image shows “spokes” on the B ring visible on the right side of the panel. The thin, thread-like F ring is easily visible just outside the A ring.

The inner C ring is the faintest of the three, but can still be detected with high-quality Earth-based telescopes. These three ring systems have a much finer structure within them, consisting of hundreds of thin rings within each. And there are several small breaks within these systems, similar to the Cassini division, but narrower. Most well-known of these is the Encke gap within the A system.[2] It is possible, though very challenging, to see the Encke gap in a high-quality backyard telescope under ideal conditions.

Another very faint ring system was discovered in 1966. Now referred to as the E ring, it is actually a torus of material rather than a flat, thin disk. It is over twice the distance from Saturn’s atmosphere as the A ring. The Cassini spacecraft found that the E ring is comprised of material ejected in geysers from Saturn’s moon Enceladus.

The four unmanned spacecraft that have visited Saturn have vastly improved our knowledge of the rings, since they have imaged features that are not easily detected from Earth. Voyager 1 discovered the D ring, a very faint system that lies inside the C ring and extends very nearly to the outer atmosphere of Saturn. Pioneer 11 discovered the F ring. Unlike the other rings which appear as broad sheets, the F ring consists of a single primary strand and a secondary thread that appears to twist around the primary. The F ring lies just outside the A ring the two are separated by the Roche division. A faint G ring has also been discovered lying between the F and E rings. All these rings orbit in the plane of Saturn’s equator, and their particles revolve around Saturn prograde – in the same direction Saturn rotates.

This night-side image of Saturn was taken by the Cassini spacecraft. The fainter rings are easily visible due to scattered sunlight. Note that the Cassini Division appears bright rather than dark, revealing that it is not completely empty.

More recently, astronomers have found evidence of an extremely faint but enormous ring at a much greater distance from Saturn. This Phoebe ring extends from about 3.8 million miles to 10.1 million miles away from Saturn, and encompasses the orbit of Saturn’s moon Phoebe. The ring lies in the plane of Saturn’s orbit – not Saturn’s equator, and consequently is tilted relative to all the other rings by 27 degrees. The Phoebe ring orbits retrograde – the opposite direction of Saturn’s rotation, as does the moon Phoebe. This enormous ring is thought to have been produced by material ejected from Phoebe.

This infrared image shows Saturn’s enormous Phoebe ring.

Saturn’s rings are a transient phenomenon. They will not last forever. In fact, they cannot last billions of years. This is because a number of processes cause the particles in the rings to erode or spiral inward over time. Collisions between the particles results in a net loss of orbital energy. The very smallest particles are subject to radiation pressure, which can degrade their orbit. Gravitational perturbations caused by Saturn and its moons will affect the orbits of the particles in the rings. And the magnetic field of Saturn will produce a force on any charged particles. Most secularists now agree that rings cannot last billions of years. They therefore think that such rings are a recent formation in a very old solar system. But what is the probability that we would be so fortunate as to live at a time when all four of the large planets have recently developed rings?

These two Cassini images each show Saturn from a perspective that is not possible from Earth. As such, they can only be achieved by a spacecraft. The left panel shows Saturn in a crescent phase, indicating that it was taken from a position farther from the sun than Saturn is (which Earth can never be). The right panel shows an overhead view of Saturn’s northern hemisphere – an angle that cannot be seen from Earth.

Observing Saturn

When people have the opportunity to see Saturn for the first time in a backyard telescope, the reaction is almost always the same: “Wow!” It won’t look as big or as sharply focused as the wonderful Hubble or other spacecraft images we see in textbooks. Nonetheless, there is something magical about the inimitable experience of seeing this little gem with your own eyes. The rings give Saturn a unique 3-dimensional appearance unrivaled in beauty. Yet, this seemingly little jewel is far larger than Earth and only appears tiny because we are seeing it from nearly a billion miles away. But what details can you expect to see on Saturn?

Saturn’s appearance in a telescope varies dramatically depending on where Saturn is in its 29.5-year orbit. It appears to observers on Earth as if Saturn’s tilt gradually changes from a maximum of 27 degrees, to zero degrees, to -27 degrees, back to zero degrees and then finally back to 27 degrees. The complete cycle lasts 29.5 years – the same as Saturn’s orbital period around the sun. In reality, Saturn’s equator is always tilted 27 degrees relative to its orbital plane. But, as Saturn orbits the sun, the inner planets observe Saturn from different perspectives. Consequently, twice every Saturn orbit, we see Saturn edge-on. This happens roughly every 15 years, when Saturn experiences its fall or spring equinox.

These Hubble Space Telescope images of Saturn were taken over several years, and reveal a changing perspective as Saturn orbits the sun. (NASA, The Hubble Heritage Team, R.G. French, J. Cuzzi, L. Dones, J. Lissauer)

In the weeks surrounding the moment when Saturn is exactly edge-on from our perspective, the rings cannot be seen at all due to their thin vertical extent. This gives Saturn a very unusual, “ringless” appearance. In the months before or after this moment, when the rings are tilted only slightly from our perspective, they appear as a thin line segment sticking through Saturn. On the other hand, when Saturn passes its summer or winter solstice, we see Saturn and its rings at their maximum tilt of nearly 27 degrees, and Saturn looks really spectacular. The last maximum apparent tilt occurred in 2017. Note that if God had not tilted Saturn’s rotation axis relative to its orbit, Saturn would always appear edge-on from Earth and we would never see those glorious rings.

This 1996 Hubble image shows Saturn nearly edge-on. If the Lord had not tilted Saturn’s rotation axis, Saturn would always appear like this from Earth. Image credit: Erich Karkoschka and NASA/ESA

The gradual change of Saturn’s apparent tilt is complicated by the fact that Earth also orbits the sun. And the plane of Earth’s orbit is not exactly the same as the plane as Saturn’s orbit – though they are very similar. Consequently, Earth is sometimes just above the plane of Saturn’s orbit, and sometimes just below this plane. The Earth of course crosses this plane twice every year. Likewise, the Earth is sometimes a bit closer to Saturn, and at other times a bit farther when the two planets are on opposite sides of the sun. Hence, a time-lapse animation of Saturn as seen from Earth shows a rapid (one year) wobble due to Earth’s orbit, combined with a slower gradual change of apparent tilt due to Saturn’s orbit around the sun over the course of 29.5 years.

This combination can lead to some interesting effects around the time Saturn appears edge-on. In some cases, Saturn can appear to be edge-on three times in a row over the course of several months. This happens when Saturn reaches an equinox at about the same time that Earth crosses the plane of Saturn’s orbit from the same direction. This situation occurred in the mid-1990s when Saturn appeared edge-on in May 1995, in August 1995, and again in February 1996. In other cases, Saturn merely appears edge-on once during its equinox crossing, as it did in September 2009. The next edge-on appearance will be a single event in March 2025. However, the 2038-2039 crossing will be a triple (July 2038, October 2038, and April 2039). Saturn’s rings can also seem to be invisible when the planet is edge-on relative to the sun, but not relative to Earth. In such a case, the rings are not illuminated except on their thin leading edge.

Time-lapse animation of Saturn over its 29.5 year orbit shows its changing perspective as viewed from the sun (left panel) and Earth (right panel). The rapid wobble on the right panel is due to Earth’s orbit around the sun. Note the triple edge-on effect as seen from Earth.

Aside from the enjoyment of seeing a rare ringless Saturn, the edge-on events of Saturn do have another advantage. They are the best time to attempt to observe Saturn’s fainter, inner moons. Saturn has 82 known moons. The inner 23 moons orbit approximately in the same plane as Saturn’s rings, and relatively close to Saturn.[3] Several of these moons orbit just outside the main ring system. The brightness of Saturn’s rings can make it difficult, though not impossible, to detect these faint moons in a backyard telescope. But when Saturn appears edge-on, the rings disappear and the moons stand out. Furthermore, at such a time, these inner moons all appear in a straight line since their orbital plane appears edge-on. This makes them even easier to detect. So take advantage of the next edge-on appearance of Saturn in March 2025.

However, Saturn is most glorious when it appears maximally tilted from our perspective: either positive 27 degrees so that we see Saturn’s north pole, or negative 27 degrees when we can see the south pole. At such times, even the far side of Saturn’s rings can be seen extending just above or below the pole from our perspective. At times of maximum tilt, the internal structure of the rings is most easily visible. A backyard telescope will often reveal the Cassini division, as well as the noticeable brightness difference between the A and B rings. You can often see the shadow that the rings cast on the planet, or the shadow that the planet casts on the far side of the rings.[4]

Regardless of where Saturn is in its orbit, the planet is best viewed when at opposition – when the Earth is most directly between Saturn and the sun. This happens roughly once per year.[5] During this time, the Earth is closest to Saturn, and so the planet appears slightly larger and brighter than it does months before or after the event. This is also true for the other planets. But with Saturn, we get another bonus on the night of opposition. At that time, sunlight scatters directly back from Saturn’s rings, and they appear noticeably brighter than they do at any other time. This is called the Seeliger effect. The effect lasts only for a few days surrounding opposition.

Hubble image of Saturn during its 2019 opposition. The rings appear especially bright due to the Seeliger effect.

If you ever have the opportunity to observe Saturn through a telescope, I highly recommend you take it. It’s quite an experience. But we are so blessed to live in a time when advances in technology have allowed superb Earth-based and space-based images of Saturn that are available to all. Who knows what other treasures the Lord has placed in His creation for us to discover?

[1] This is the estimated temperature at a depth corresponding to 1 bar of atmospheric pressure.

[2] Breaks between systems of rings are called divisions. The Cassini division is a break between the A and B system. Breaks within a system of rings is called a gap. Hence, the Encke gap is within the A ring system. This nomenclature is rather modern, and older literature will sometimes refer to the Encke division.

[3] Typically, you can see one to six of Saturn’s moons in a backyard telescope, depending on your skill, the quality of the instrument, and the darkness of the sky. However, more can often be seen when the rings appear edge-on.

[4] The shadow of the planet on the rings is most easily seen when Saturn is several months before or after opposition.


Other Theories why Saturn has Rings

Some say that there were once many more large moons orbiting Saturn, like the moon Titan, but that during some turbulent period in galactic history, gravitational forces ripped those moons apart into tiny dusty pieces which then became the rings. A similar process is happening to Mars, albeit on a much smaller scale as its two small moons begin to degrade in their orbit and integrity.

Other astronomers suggest that Saturn simply exists in a super dirty part of our solar system. Not only does Saturn have massive rings but it also has the largest number of moons out of any planet in the solar system. This suggests that perhaps Saturn simply formed in an area of space that had a much higher concentration of nearby materials which formed its extensive moon and ring systems. Saturn’s large size and extensive gravitational field would have collected any nearby material that was not pulled towards Jupiter or Uranus. If there was simply more material in the area, it would have gravitated towards Saturn giving it more materials in its sphere of influence.

So Saturn has rings because, presumably, most if not all gas giants have rings. Why Saturn’s rings are so reflective and large is a subject for debate that has no clear answers at this time. As we continue to explore Saturn via telescope and flyby we continue to learn more and more about this ancient and fascinating planet.

Next time you look through your best telescope for planets and you find Saturn in your eyepiece. You will know a lot more about Saturn’s rings. I have already discovered Who Discovered The Rings of Saturn and here How Many Rings Does Saturn Have?. Want to dig a bit deeper on What are Saturn’s rings made out of we have you covered in our post.


What affects our viewing of Saturn…

Their cyclical tilt has an impact on how well one can see Saturn’s rings through a telescope. Their widest opening to date reached the twenty-seven degrees, as recorded in 2017.

Up until then, the gap between them wasn’t as huge as it was in 1988 when it first opened to its fullest. Currently, the northern face of the rings is almost reaching the twenty-two degrees mark.

According to sources, once 2025 rolls around, they will appear edge-on when observing them from planet Earth, whereas they will incline to the same opening degree they had in 2017 by May 2032, which means that it will be almost impossible to look at them.

This might seem a bit discouraging but, in the meantime, keeping an eye on the width of the gap will help to have a clear idea as to how much of the rings one would be able to see.

Saturn’s rings also influence how the planet looks like through a high-end telescope. The shadow that they cast on the planet gives it a 3-D appearance.

This becomes more noticeable once the observer recognizes both the shadows’ and sunlight’s direction. The limb-darkened edges give Saturn the appearance of yellow and brown marble.

However, this impressive “look”, for lack of a better word to describe it, doesn’t translate to the rings. They are said to look as if they were made of paper in comparison, with little to no details at a first glance.

Fret not, since this can be seen with a small scope during the times where it can be seen in its full glory.

Easy to get confused…

It is widely known that planets tend to shine steadily from the distance, something might get them confused with actual stars.

Of course, Saturn is no exception to this rule, but there’s a twist: Its shine has a golden tint to it that can be enhanced with Astronomy Binoculars, as well as this particular color being detected by planet telescopes.

However, taking a look at this planet can be rather tricky, mainly because of how tiny it is when compared to other celestial beings that are seen through any kind of model, regardless of whether it’s professional or made for beginners.

Its diameter only reaches up to twenty-one arcseconds on a good day, and let’s not get started with its rings, which are 2.25 times as wide as the sphere that comprises Saturn’s body, smaller than Jupiter’s.

With all of this in mind, let’s jump right into the main subject of this article: Seeing Saturn’s rings from a telescope.

Every expert agrees that this is an enjoyable sight that needs to be experienced at least once.

Of course, a household telescope won’t provide an image with a similar quality to the more professional models, but it will bring the same satisfaction, mainly because of how beautiful this massive planet is.

For the smaller variant, it is recommended to have a magnification of 25x, as well as an eyepiece of 15 millimeters, preferably through a Dobsonian telescope.

Eyepiece is crucial…

The size of the telescope and eyepiece is crucial to how much one would be able to see from Saturn since it has an impact on the image quality.

Regardless of what many could think, increasing the magnifying range won’t make Saturn appear in full detail, far from it.

Doing so will only result in the image looking even more blurry, something that would be counter-productive for someone who has been looking forward to stargazing with a clear image of what they were looking for.

To fix the issue, I advise getting a telescope with a wide enough aperture, which will allow the observer to see both planets and other celestial objects that catch their eye.

Saturn’s rings should be visible regardless of the size and magnifying range of the telescope.

It is said that one can achieve good results with equipment that reaches the 25x mark. Many observers have even been able to take a closer look at its rings with a 6-inch scope when the viewing conditions are optimal.

Also, eyepieces between 9 and 30 millimeters are capable of providing good results. I recommend adding a 2x Barlow lens into the equation, mainly because this would enhance the magnification.

Need some more help on Viewing Saturn With and Without a Telescope we have a guide for you.


Can you see Saturn without a telescope?

Even though Saturn is very far away from us, it might surprise you to find out you can sometimes watch it even without help from optic devices. Just go out, look at the sky and you might find it.

Saturn is the last and faintest of the denominated bright planets. That means the planets that can be sometimes seen with the naked eye.

Because it is the last one though, the conditions usually have to be great for it to appear and it might be difficult to differentiate it from a star.

The downside of this approach, of course, is that you will not be able to distinguish its rings or look at it with the level of detail you’d get with a telescope. It simply looks like another dot in the night sky.

Elena is a Canadian journalist and researcher. She has been looking at the sky for years and hopes to introduce more people to the wonderful hobby that is astronomy.

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About Little Astronomy



Hi! I’m Elena. I’m a journalist who has been into astronomy since I was a kid. I founded this site to share tips and facts about astronomy and telescopes.

If you are new around here and you want to get started with the hobby, take a look at our recommended gear page.


Saturn’s rings: less than meets the eye?

The B ring is the brightest of Saturn’s rings when viewed in reflected sunlight. Image credit: NASA/JPL-Caltech/Space Science Institute. It seems intuitive that an opaque material should contain more stuff than a more translucent substance. For example, muddier water has more suspended particles of dirt in it than clearer water. Likewise, you might think that, in the rings of Saturn, more opaque areas contain a greater concentration of material than places where the rings seem more transparent.

But this intuition does not always apply, according to a recent study of the rings using data from NASA’s Cassini mission. In their analysis, scientists found surprisingly little correlation between how dense a ring might appear to be &mdash in terms of its opacity and reflectiveness &mdash and the amount of material it contains.

The new results concern Saturn’s B ring, the brightest and most opaque of Saturn’s rings, and are consistent with previous studies that found similar results for Saturn’s other main rings.

The scientists found that, while the opacity of the B ring varied by a large amount across its width, the mass &mdash or amount of material &mdash did not vary much from place to place. They “weighed” the nearly opaque centre of the B ring for the first time &mdash technically, they determined its mass density in several places &mdash by analysing spiral density waves. These are fine-scale ring features created by gravity tugging on ring particles from Saturn’s moons, and the planet’s own gravity. The structure of each wave depends directly on the amount of mass in the part of the rings where the wave is located. Saturn’s B ring is the most opaque of the main rings, appearing almost black in this Cassini image taken from the unlit side of the ringplane. Image credit: NASA/JPL-Caltech/Space Science Institute. “At present it’s far from clear how regions with the same amount of material can have such different opacities. It could be something associated with the size or density of individual particles, or it could have something to do with the structure of the rings,” said Matthew Hedman, the study’s lead author and a Cassini participating scientist at the University of Idaho, Moscow. Cassini co-investigator Phil Nicholson of Cornell University, Ithaca, New York, co-authored the work with Hedman.

“Appearances can be deceiving,” said Nicholson. “A good analogy is how a foggy meadow is much more opaque than a swimming pool, even though the pool is denser and contains a lot more water.”

Research on the mass of Saturn’s rings has important implications for their age. A less massive ring would evolve faster than a ring containing more material, becoming darkened by dust from meteorites and other cosmic sources more quickly. Thus, the less massive the B ring is, the younger it might be &mdash perhaps a few hundred million years instead of a few billion.

“By ‘weighing’ the core of the B ring for the first time, this study makes a meaningful step in our quest to piece together the age and origin of Saturn’s rings,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. “The rings are so magnificent and awe-inspiring, it’s impossible for us to resist the mystery of how they came to be.” Some parts of Saturn’s B ring are up to 10 times more opaque than the neighbouring A ring, but the B ring may weigh in at only two to three times the A ring’s mass. Image credit: NASA/JPL-Caltech/Space Science Institute. While all the giant planets in our solar system (Jupiter, Saturn, Uranus and Neptune) have ring systems of their own, Saturn’s are clearly different. Explaining why Saturn’s rings are so bright and vast is an important challenge in understanding their formation and history. For scientists, the density of material packed into each section of the rings is a critical factor in ascribing their formation to a physical process.

An earlier study by members of Cassini’s composite infrared spectrometer team had suggested the possibility that there might be less material in the B ring than researchers had thought. The new analysis is the first to directly measure the density of mass in the ring and demonstrate that this is the case.

Hedman and Nicholson used a new technique to analyse data from a series of observations by Cassini’s visible and infrared mapping spectrometer as it peered through the rings toward a bright star. By combining multiple observations, they were able to identify spiral density waves in the rings that aren’t obvious in individual measurements.

The analysis also found that the overall mass of the B ring is unexpectedly low. It was surprising, said Hedman, because some parts of the B ring are up to 10 times more opaque than the neighbouring A ring, but the B ring may weigh in at only two to three times the A ring’s mass.

Despite the low mass found by Hedman and Nicholson, the B ring is still thought to contain the bulk of material in Saturn’s ring system. And although this study leaves some uncertainty about the ring’s mass, a more precise measurement of the total mass of Saturn’s rings is on the way. Previously, Cassini had measured Saturn’s gravity field, telling scientists the total mass of Saturn and its rings. In 2017, Cassini will determine the mass of Saturn alone by flying just inside the rings during the final phase of its mission. The difference between the two measurements is expected to finally reveal the rings’ true mass.


Composition

What are the rings of Saturn – What are they made of?

Early Theories of Composition
The knowledge we have today of Saturn has not always been so. Early astronomers such as Galileo first developed theories which have either been proved wrong or altered and developed further. When Galileo first seen the rings in 1610 through a telescope, he described them as two arm-like ears sticking out from the planet. 17 Later, in 1656 astronomer Christiaan Huygens discovered that the ears were not ears after all but actually circle around the planet in a ring. 14 His theory was that Saturn had a solid, thin, flat ring surrounding Saturn. 5 New theories have since developed from the early astronomers Galileo and Huygens discoveries.

Later Theories
From the theory of a single ring surrounding the planet developed the theory of there actually being multiple rings. French astronomer Jean Chapelain surmised that the rings were made up of small particles orbiting around Saturn, and later the Scottish physicist James Clerk Maxwell confirmed this theory and stated that the particles had to be small or they would be pulled in by Saturn’s gravity until they collided into the planet. 17 These astronomers theorized that the rings were created when comets or asteroids collided, shattering into pieces and spreading around the planet. 17 Another theory suggests that the rings are composed of debris that failed to clump into moons because of the gravitational pull of Saturn continuously moving the debris around, or possibly the storms and lightning that Saturn produces. 16

What research led us to know what the rings are composed of today?

As previously mentioned, Galileo was the first astronomer to view Saturn through a telescope around 400 years ago. 8 Upon gazing at the planet Saturn, he discovered what he thought to be two “moons” surrounding the planet. These moons turned out to be the rings as we know them today.

Figure 5. Galileo’s initial drawing of Saturn

(Image Credit: www.myastrologybook.com)

Although it was impressive that Galileo was able to discover the rings of Saturn, he was unable to figure out what the rings are made of. In fact, it took another 342 years for humans to be able to test the composition of Saturn’s rings. This was accomplished by G.P. Kuiper in 1952, who used ground-based near-infrared spectroscopy to determine that the rings of Saturn are made up of (or at least covered by) H2O in the form of frost or ice. 9 Spectroscopy is the process of determining the makeup of an object by the intensity of different wavelengths that the object absorbs or emits. 10 By using spectroscopy, scientists can determine what elements are present in an object.

Figure 6. Labelled Diagram of Saturn

Later, in the 1970s and 80s, the first microwave observations of the rings were conducted. 11 A microwave observation conducted by Grossman (1990) supported Kuiper’s findings, and even suggested that the rings are made up of almost pure ice with silicate material making up around 1% of the ring’s composition. 12 These findings were further supported by the Voyager radio occultation experiment which was performed by Tyler et al. (1983) during the Voyager expeditions. 13 The Voyager expeditions refer to a set of twin shuttles that were launched in 1977 to explore the outer planets of our solar system. While the Voyager 1 was passing close to Saturn, G.L. Tyler et al. performed an experiment in which they measured the radio occultation of Saturn’s rings by firing radio signals from the Voyager 1 spacecraft close to earth which travelled through the rings of Saturn to be received by the 64-m-diameter parabolic antenna at the NASA Deep Space Network receiving site near Madrid, Spain. 13 They then were able to measure the amount of signal that was cut off by Saturn’s rings and extrapolate information regarding the composition of the rings. The experiment performed by Tyler et al. 13 further confirmed the findings of Kuiper that the rings are made up of almost entirely ice.

Figure 7. Cosmic Radio Occultation

The Composition of Saturn’s Rings
Through these observations and theories, scientists have discovered that in fact the rings of Saturn are composed of particles and debris. 17 The debris comes from broken up pieces of comets, asteroids, and dead moons. the particles are made up of ice, dust/mud, and rock.
Along with being able to determine the composition of the rings, scientists have made numerous observations of the rings regarding their size, temperature, placement, and their unique traits. The following list depicts these observations:
Size
* Particle size varies from the size of a grain of sand to the size of a mountain. 14
* The rings are thin at approximately 33 feet think, reaching up to 2 miles (3km) in some spots. 15
* The rings extend out to 175,000 miles (282,000) from the plant. 15
* The inner moons of Saturn effect the shape of the rings by orbiting between them and dividing them, constraining their width. 15
Temperature
* The Cassini spacecraft took the temperature of the rings on the unlit side and resulted in -264.1° and -333.4° Fahrenheit. (-163° to -203° Celsius). 15
Placement
* The rings are all relatively close to one another with the exception of the Cassini Gap between ring A and ring B that extends 2,920 miles. 15
Spokes (unique trait)
* A unique feature of the rings that essentially look like lines that orbit with the rings called spokes. 15
* One theory is Icy particles above the rings surface via electrostatic charge. 15
* Another theory is that they are electrically charged sheets of dust-sized particles from meteors impacting the rings. 5
* Scientists also speculated that they could be electron beans from Saturn’s lightning. 5
* They are temporary, can form and disappear over a few hours, and discovered by the Cassini mission in 2005. 15

Figure 9. Particles above the rings viewed from Cassini on September 22, 2009.


Why Only Saturn Has Visible Rings - Astronomy

Why are Saturn's rings flat? Why isn't the debris dispersed equally around the whole planet?

That's an excellent question, and the key to the answer is the the entire system is spinning. Each ring particle is orbiting Saturn, like a tiny moon. Since there are a lot of ring particles, from time to time, they run into one another.

Let's ignore the question of exactly how the rings formed (which is a bit controversial) and just assume that at first, there are particles orbiting in every direction. However, the majority ofthe particles will be orbit in one direction or the other (in the case of planetary rings, counter-clockwise as viewed from the north).

Now, particles that are orbiting in the other direction (which we call retrograde) will be moving fast relative to the other particles (think about someone who accidentally ends up going the wrong way on the highway!), so they will be more likely to suffer a collision, and the collision will be more violent. Either the particle will get turned around, or it will be pulverized! Either way, there will be fewer and fewer retrograde particles as time goes on.

Among the particles that are moving counter-clockwise, some will be on orbits that are tilted (or, as astronomers say, inclined), and their inclinations will be more-or-less random. That means that a particle on an inclined path that happens to be moving upward has a good chance of encountering another inclined particle that happens to be moving downward. Thus, inclined particles will clonk into each other and some of the upward motion of one will cancel out the downward motion of the other, leaving both particles on less inclined orbits. This is how the system will tend to settle down into a disk.

As more and more particles settle into the disk, then the remaining inclined particles will have a very dangerous journey! Twice per orbit they have to pass through the disk, where they are likely to suffer a collision.

Particles in the disk, on the other hand, will all be moving the same way at approximately the same speed. Though they might jostle their neighbors from time to time, they do not suffer violent collisions like the inclined particles do.

Over time (a very short time, as it turns out!) the inclined particles will lose their inclination or be destroyed, leaving a nice, flat ring system.

We see this disk-forming process, not only in planetary rings, but in many other astrophysical contexts, such as young solar systems and disks around black holes.

This page was last updated June 28, 2015.

About the Author

Britt Scharringhausen

Britt studies the rings of Saturn. She got her PhD from Cornell in 2006 and is now a Professor at Beloit College in Wisconson.