Saturn can be seen with the naked eye. It is the fifth brightest object in the solar system and is also easily studied through binoculars or a small telescope.
Saturn was known to the ancients, including the Babylonians and Far Eastern observers. It is named for the Roman god Saturnus, and was known to the Greeks as Cronus.
Saturn is the flattest planet. Its polar diameter is 90% of its equatorial diameter, this is due to its low density and fast rotation. Saturn turns on its axis once every 10 hours and 34 minutes giving it the second-shortest day of any of the solar system’s planets.
Saturn orbits the Sun once every 29.4 Earth years. Its slow movement against the backdrop of stars earned it the nickname of “Lubadsagush” from the ancient Assyrians. The name means “oldest of the old”.
Saturn’s upper atmosphere is divided into bands of clouds. The top layers are mostly ammonia ice. Below them, the clouds are largely water ice. Below are layers of cold hydrogen and sulfur ice mixtures.
Saturn has oval-shaped storms similar to Jupiter’s. The region around its north pole has a hexagonal-shaped pattern of clouds. Scientists think this may be a wave pattern in the upper clouds. The planet also has a vortex over its south pole that resembles a hurricane-like storm.
Saturn is made mostly of hydrogen. It exists in layers that get denser farther into the planet. Eventually, deep inside, the hydrogen becomes metallic. At the core lies a hot interior.
Saturn has the most extensive rings in the solar system. The Saturnian rings are made mostly of chunks of ice and small amounts of carbonaceous dust. The rings stretch out more than 120,700 km from the planet, but are are amazingly thin: only about 20 meters thick.
Saturn has 150 moons and smaller moonlets. All are frozen worlds. The largest moons are Titan and Rhea. Enceladus appears to have an ocean below its frozen surface.
Titan is a moon with complex and dense nitrogen-rich atmosphere. It is composed mostly of water ice and rock. Its frozen surface has lakes of liquid methane and landscapes covered with frozen nitrogen. Planetary scientists consider Titan to be a possible harbour for life, but not Earth-like life.
Four spacecraft have visited Saturn. Pioneer 11, Voyager 1 and 2, and the Cassini-Huygens mission have all studied the planet. Cassini orbited Saturn from July 2004 until September 2017, sending back a wealth of data about the planet, its moons, and rings.
While all the gas giants in our solar system have rings none of them are as extensive or distinctive as Saturn’s. The rings were discovered by Galileo Galilei 1610 who observed them with a telescope. The first ‘up close’ view of the rings were by Pioneer 11 spacecraft which flew by Saturn on September 1, 1971.
Saturn’s rings are made up of are billions of particles that range in size from tiny dust grains to to objects as large as mountains. These are made up of chunks of ice and rock, believed to have come from asteroids comets or even moons, that broke apart before they reached the planet.
Saturn’s rings are divided into 7 groups, named alphabetically in the order of their discovery (Outwards from Saturn; D, C, B, A, F, G and E). The F ring is kept in place by two of Saturn’s moons, Prometheus and Pandora, these are referred to as ‘shepherd moons’. Other satellites are responsible for creating divisions in the rings as well as shepherding them.
1. Saturn is the least dense planet in the Solar System
Saturn has a density of 0.687 grams/cubic centimeter. Just for comparison, water is 1 g/cm3 and the Earth is 5.52. Since Saturn is less dense than water, it would actually float like an apple if you could find a pool large enough. Of course, why you’d want to ruin a pool with all that hydrogen, helium and ices…
2. Saturn is a flattened ball
Saturn spins so quickly on its axis that the planet flattens itself out into an oblate spheroid. Seriously, you see this by eye when you look at a picture of Saturn; it looks like someone squished the planet a little. Of course, it’s the rapid spinning that’s squishing it, causing the equator to bulge out. While the distance from the center to the poles is 54,000 km, the distance from the center to the equator is 60,300 km. In other words, locations on the equator are approximately 6,300 km more distant from the center than the poles. We have a similar phenomenon here on Earth, where points on the equator are more distant from the center of the Earth, but on Saturn, it’s much more extreme.
3. The first astronomers thought the rings were moons.
When Galileo first turned his rudimentary telescope on Saturn in 1610, he could see Saturn and its rings, but he didn’t know what he was looking at. He thought that the rings might actually be two large moons stuck to either side of Saturn – ears maybe? It wasn’t until 1655 that the Dutch astronomer Christian Huygens used a better telescope to observe Saturn. He had the resolution to realize that the moons on either side of Saturn were actually rings: “a thin, flat ring, nowhere touching, and inclined to the ecliptic.” Huygens was also the first person to discover Saturn’s largest moon, Titan.
4. Saturn has only been visited 4 times by spacecraft
Only 4 spacecraft sent from Earth have ever visited Saturn, and three of these were just brief flybys. The first was Pioneer 11, in 1979, which flew within 20,000 km of Saturn. Next came Voyager 1 in 1980, and then Voyager 2 in 1981. It wasn’t until Cassini’s arrival in 2004 that a spacecraft actually went into orbit around Saturn and captured photographs of the planet and its rings and moons. Unfortunately, there are no future plans to send any more spacecraft to Saturn. A few missions have been proposed, including such radical concepts as a sailboat that could traverse the liquid methane lakes on Titan.
5. Saturn has 62 moons
Jupiter has 67 discovered moons, but Saturn is a close second with 62. Some of these are large, like Titan, the second largest moon in the Solar System. But most are tiny – just a few km across, and they have no official names. In fact, the last few were discovered by NASA’s Cassini orbiter just a few years ago. More will probably be discovered in the coming years.
6. The length of a day on Saturn was a mystery until recently
Determining the rotation speed of Saturn was actually very difficult to do, because the planet doesn’t have a solid surface. Unlike Mercury, you can’t just watch to see how long it takes for a specific crater to rotate back into view; astronomers needed to come up with a clever solution: the magnetic field. To determine the rotational speed of Saturn, astronomers had to measure the rotation of the planet’s magnetic field. By one measurement, Saturn takes 10 hours and 14 minutes to turn on its orbit, but when Cassini approached Saturn, it clocked the rotation at 10 hours and 45 minutes. Astronomers now agree on an average day of 10 hours, 32 minutes and 35 seconds.
7. Saturn’s rings could be old, or they could be young.
It’s possible that Saturn’s rings have been around since the beginning of the Solar System – around 4.54 billion years ago. Or maybe they’re relatively brand new compared to the age of Saturn. Astronomers still don’t fully understand the origin of Saturn’s rings.
They might have formed recently, when a 300-km ice moon was torn apart by Saturn’s gravity, forming a ring around the planet. It’s also possible that they’re the left over material when Saturn formed in the solar nebula. The material in the rings might have gotten jostled by Saturn’s gravity, and never could pull together into a cohesive Moon.
But astronomers have also found that the ring material looks just too clean to have formed so long ago, and could be as young as 100 million years old. It’s all just a big mystery.
8. Sometimes the rings disappear
Well, they don’t actually disappear, but they look like they’re going away. Saturn’s axis is tilted, just like Earth. From our point of view, we see Saturn’s changing position as it takes its 30-year journey around the Sun. Sometimes, the rings are fully open, and we see them in all their glory, but other times we see the rings edge on – it looks like they’ve disappeared. This happened in 2008-2009, and will happen again in 2024-2025.
9. You can see Saturn with your own eyes
Saturn appears as one of the 5 planets visible with the unaided eye. If Saturn is in the sky at night, you can head outside and see it. To see the rings and the ball of the planet itself, you’ll want to peer through a telescope. But you can amaze your friends and family by pointing out that bright star in the sky, and let them know they’re looking at Saturn.
Saturn is the sixth planet from the Sun, and last of the planets known to ancient civilizations. It was known to the Babylonians and Far Eastern observer.
Saturn is one of five planets able to be seen with the naked eye. It is also the fifth brightest object in the solar system.
In Roman mythology Saturn was the father of Jupiter, king of the gods. This relationship makes sense given that the planets Saturn and Jupiter are similar in so many respects, including size and composition. The Greek counterpart is known as Cronus.
The most common nickname for Saturn is “The Ringed Planet”, a nickname arising from the large, beautiful and extensive ring system that encircles the planet. These rings are mostly made from chunks of ice and carbonaceous dust. They stretch out more than 12,700 km from the planet but are only a mere 20 meters thick.
Saturn gives off more energy than it receives from the Sun. This unusual quality is believed to be generated from the gravitational compression of the planet combined with the friction from large amount of helium found within its atmosphere.
It takes Saturn 29.4 Earth years to orbit the Sun. This slow movement against a backdrop of stars led to the planet being nicknamed “Lubadsagush” – or “oldest of the old” – by the ancient Assyrians.
Saturn has the fastest winds of any other planet in our solar system. These winds have been measured at approximately 1,800 km per hour (1,100 miles per hour).
Saturn is the least dense planet in the solar system. It is made mostly of hydrogen and has a density which is less than water – which technically means that Saturn would float. The layers of hydrogen get denser further into the planet, eventually becoming metallic and leading to a hot interior core.
Saturn has 150 moons and smaller moonlets. All of these moons are frozen – the largest of which are Titan and Rhea. The moon Enceladus also appears to have an ocean hidden below its frozen surface.
Saturn’s moon Titan is the second largest moon in the Solar System, behind Jupiter’s moon Ganymede. It has a complex and dense atmosphere made mostly of nitrogen and is composed from water ice and rock. The frozen surface of Titan has liquid methane lakes and a landscape which is covered with frozen nitrogen. It is possible that Titan may be a harbor for life – but that life would not be similar to life on Earth.
Saturn is the flattest of the eight planets. With a polar diameter that is 90% of its equatorial diameter, Saturn is the flattest of all the planets. This is because of the planet’s low density and fast rotation speed – it takes Saturn 10 hours and 34 minutes to turn on its axis.
Saturn has oval shaped storms which are similar to those of Jupiter. Scientists believe that the hexadiagonal-shaped pattern of clouds around Saturn’s north pole may be a wave pattern in the upper clouds. There is also a vortex over the south pole which resembles hurricane storms on Earth.
Saturn appears a pale yellow color because its upper atmosphere contains ammonia crystals. Below this top layer of ammonia ice are clouds that are largely water ice. Even further below that are layers of sulfur ice and cold hydrogen mixtures.
Saturn has been visited by four spacecraft. These are Pioneer 11, Voyager 1 and 2 and the Cassini-Huygens mission. Cassini entered into orbit around Saturn on July 1, 2004 and continues to send back information about the planet, its ring and many moons.
The magnetic field on Saturn is slighter weaker than Earth’s magnetic field. Saturn’s magnetic field strength is around one-twentieth the strength of Jupiter’s
Saturn is known as a gas giant, but scientists believe it has a solid rocky core surrounded by hydrogen and helium
Saturn and Jupiter combined account for 92% of the entire planetary mass in the solar system.
The interior of Saturn is very hot, reaching temperatures of up to 11,700°C (21,000 °F).
Saturn is 1,424,600,000 km from the Sun. This is around 0.9 billion miles.
More information and facts about Saturn
Other than Earth, Saturn is easily the most recognizable planet in the Solar System. The reason for this is obvious. Although the other gas giants possess a planetary ring system, none can match the size or beauty of the one found encircling Saturn. Saturn is the last of the planets known to ancient civilizations. It is also one of the least understood in modern times. With the Cassini-Huygens planetary mission that is currently underway, scientists hope to not only learn more about Saturn, but also Saturn’s moons and its planetary ring system.
Saturn’s atmosphere is composed of roughly 96% hydrogen and 4% helium, with trace amounts of ammonia, acetylene, ethane, phosphine and methane. It has a thickness of approximately 60 km. In the highest layer of the atmosphere, wind speeds reach 1,800 km/h, easily some of the fastest in the entire Solar System.
Although not as visible as those seen on Jupiter, Saturn does possess a horizontally banded cloud pattern. Furthermore, these bands are considerably wider near Saturn’s equator than those found at Jupiter’s equator. These cloud patterns were unknown until the Voyager missions beginning in the 1970s. Since that time, technology has increased to the point that Earth0based telescopes can now view them.
Another fascinating phenomenon that can be found in Saturn’s atmosphere is the appearance of great white spots. These are storms on Saturn, which are analogous to the Great Red Spot found on Jupiter, though they are much shorter lived. The Hubble Space Telescope observed such a storm in 1990, though it was not present when the Voyager spacecraft had flown by in 1981. Based on historical observations, it appears that these storms are periodic in nature, occurring approximately once per Saturnian orbit.
The interior of Saturn is believed to be extremely similar to Jupiter’s in the composition of its three layers. The innermost layer is a rocky core between 10-20 times as massive as the Earth. The core is encased in a layer of liquid metallic hydrogen. The outermost layer is composed of molecular hydrogen (H2). The only significant difference between the interiors of Saturn and Jupiter is thought to be the thickness of the two outer layers. Whereas Jupiter has a metallic hydrogen layer of 46,000 km and molecular hydrogen layer of is 12,200 km, those same layers on Saturn have a thickness of 14,500 km and 18,500 km, respectively.
Saturn, like Jupiter, emits approximately 2.5 times more radiation than it receives from the Sun. This is due to the Kelvin-Helmholtz mechanism, which essentially creates energy through gravitational compression of the planet due to its enormous mass. However, unlike Jupiter, the total amount of energy emitted cannot be accounted for through this process alone. Instead, scientists have suggested that the planet generates additional heat through the friction of helium rain. A unique feature of Saturn is that it is the least dense planet in the Solar System. Although Saturn may have a dense, solid core, the large gaseous outer layer of the planet makes its average density a mere 687 kg/m3. As result, Saturn is lighter than water.
Orbit & Rotation
The average orbital distance of Saturn is 1.43 x 109 km. This means that Saturn is, on average, about 9.5 times the distance from the Earth to the Sun. The result of such a long distance is that it takes sunlight about an hour and twenty minutes to reach Saturn. Moreover, given Saturn’s distance from the Sun, it has a year lasting 10,756 Earth days; that is, about 29.5 Earth years.
At .0560, Saturn’s orbital eccentricity is the third greatest behind Mercury’s and Mars’. The effect of this large eccentricity is a substantial distance between the planet’s perihelion (1.35 x 109 km) aphelion (1.50 x 109 km) of about 1.54 X 108 km.
Saturn’s axial tilt of 26.73 is very similar to the Earth’s. Thus Saturn also experiences seasons like the Earth. However, due to Saturn’s distance from the Sun, it receives significantly less solar radiation year-round, and so Saturn’s season are much subtler than those on Earth.
Much like Jupiter, Saturn is very interesting when it comes to its rotation. Having a rotational speed of roughly 10 hours 45 minutes, Saturn is second only to Jupiter for the fastest rotation in the Solar System. This extreme rotation causes the planet’s shape to take on the shape of an oblate spheroid; i.e. a sphere that bulges near its equator.
A second feature of Saturn’s rotation is the different rotational speeds found between the different visible latitudes. This phenomenon is due to Saturn being primarily gaseous rather than solid.
The ring system of Saturn is the most prominent found in the Solar System. They are composed primarily of billions of tiny ice particles, with traces of dust and other debris. This composition explains why the rings are visible to Earth-based telescopes—ice is very reflective of sunlight.
There are seven broad classifications among the rings: A, B, C, D, E, F, G, each receiving its name in the order it was discovered. The main rings most visible from Earth are A, B and C. Each ring is really just a collection of thousands of smaller rings packed very closely together. Furthermore, between each ring there are gaps. At 4,700 km and occurring between rings A and B, Cassani is the largest of these gaps.
At least 62 moons travel around Saturn. They come in a variety of sizes and compositions, from almost pure ice to rocky material, as well as a combination of both. Their journeys around the ringed planet range from half an Earth day to just over four Earth years.
One of Saturn's moons, Titan, makes up 96 percent of the mass orbiting the planet. Scientists think that Saturn's system may have originally housed two such moons, but the second broke up, creating the debris that formed the rings and smaller, inner moons. Another theory suggests that the system originally housed several large moons, similar to Jupiter's Galilean moons, but two fused into Titan. The violent collision could have scattered the debris that would have later drawn together into the smaller moons.
The colorful globe of Saturn's largest moon, Titan, passes in front of the planet and its rings in this true color snapshot from NASA's Cassini spacecraft. The north polar hood can be seen on Titan (3,200 miles or 5,150 kilometers across) and appears as a detached layer at the top of the moon here. Image released Dec. 22, 2011.
Some of the moons travel inside the gaps of the rings, clearing paths through the debris. Others orbit farther out. Several of the moons interact with one another, with their orbits moving in resonance with each other. Larger moons may trap smaller moons, keeping them nearby. Sixteen of the moons are tidally locked, with one face permanently turned toward Saturn.
The first moon was discovered in 1655. Over the next 200 years, the other seven major satellites were spotted. By 1997, astronomers on Earth had found 18 moons in orbit around the planet. The close orbit of NASA's Cassini mission, along with advances in technology for Earth-based telescopes, enabled the discovery of the rest.
In 1847, British astronomer Sir John Herschel suggested that the moons of Saturn take their names from the Titans. The mythical siblings of the Greek god Cronus — Saturn to the Romans — the Titans battled the Olympian gods and lost. Once the names of the Titans were used, the moons began to be called after other characters from Roman and Greek mythology. Only 53 of Saturn's moons have names; the rest are identified by a numerical designation relating to their year of discovery.
Let's look at the eight major moons of Saturn:
Titan is the largest of Saturn's moons and the first to be discovered. Titan is the only moon in the solar system known to have a significant atmosphere. Nitrogen and methane extend around the moon 10 times as far into space as Earth's atmosphere, sometimes falling to the surface in the form of methane rain. This atmosphere makes it one of the best potential candidates for hosting life. Titan is larger than the planet Mercury, though not nearly as massive. It hosts many hydrocarbon-filled lakes as well as extremely tall mountains, with the largest one rising to nearly 11,000 feet. This moon is the only one to have a landing craft arrive on its surface, when the Cassini mission sent the Huygens lander there in 2005.
Dione is thought to be a dense rocky core surrounded by water-ice. The tidally locked moon is heavily cratered not on its leading side but on its back side. Astronomers think a collision could have spun the moon on its axis. The moon hosts a thin oxygen atmosphere and may have a liquid ocean beneath its surface.
Enceladus contains more than 100 geysers at its south pole. Tidal heating causes portions of the icy planet to melt, spewing icy material into space from its "tiger stripes." The tiny bits of ice travel together to create Saturn's E ring. The satellite's icy surface makes it one of the brightest objects in the solar system. The moon has a subsurface ocean that may be friendly to life.
Hyperion was the last of the major satellites to be discovered. Hyperion is a small moon with an irregular appearance. The flattened object resembles an elongated potato rather than a sphere, a form that may have been created when an impact demolished a larger moon long ago. Hyperion has a spongy shape, possibly due to its low density and porous surface. Impacts seem to be absorbed by the moon, and most of the ejecta is thrown into space.
Iapetus features light and dark contrasts on its surface, giving the moon a yin-yang shape. Dark hydrocarbons falling to the moon long ago, perhaps from the nearby moon Phoebe, may have had more time to absorb more heat, gradually growing and spreading over time. Iapetus has a walnut-like shape, with its center bulging outward, and a ridge running around its equator. The moon also contains some of the highest mountains in the solar system, which may have been material from another moon. Scientists are studying ice movements (such as landslides) to do comparative work with these types of features on Earth.
Mimas has a gaping crater that gives the rocky moon a strong resemblance to fictional Death Star in the "Star Wars" movies. The impact stands out despite the fact that Mimas is one of the most heavily cratered bodies in the solar system, with overlapping impacts covering the surface. The smallest and closest orbiting of Saturn's major moons, Mimas cleared the gap known as the Cassini division between two of the planet's rings. Mimas is made up primarily of water-ice, but despite its proximity to the planet (and the resulting tidal heating that should occur), the surface of the moon remains unchanged; none of the ice seems to be melting, though such melting occurs on other, more distant moons. It is possible that there is a liquid ocean beneath its surface, although scientists say that an oval-shaped core could also explain some of Mimas' libration movements.
Rhea is a heavily cratered moon and lacks a core at its center. Instead, the entire body is composed of ice, with traces of rock mixed in, causing it to resemble a dirty snowball. The second largest of the planet's major moons, Rhea is still rather small, about half the size of Earth's moon. The satellite contains a faint oxygen atmosphere, about 5 trillion times less dense than the one found on Earth, but the only known oxygen atmosphere in the solar system. Radiation from Saturn's magnetosphere could release oxygen and carbon dioxide from the icy surface.
Tethys travels close to Saturn and feels the gravitational pull of the planet. The heat from Saturn may allow the moon's icy surface to melt slightly, filling in craters and other signs of impact. Made up almost entirely of water ice, the surface is highly reflective. A large trench crosses the moon, running diagonally from its north to south pole and spanning three-quarters of the satellite's circumference. A large crater on the other side of the moon covers nearly two-fifth of the moon's diameter and is nearly the size of Mimas. Scientists have found strange red arcs on the moon and are still struggling to explain how the arcs got there.
The minor moons
The smaller named moons of Saturn are as follows:
The unnamed moons, identified by year of discovery, are:
1. S/2004 S7
2. S/2004 S12
3. S/2004 S13 4. S/2004 S17
5. S/2006 S1
6. S/2006 S3 7. S/2007 S2
8. S/2007 S3
9. S/2009 S1
Huygens on Titan (c) NASA
The surface of Titan (c) Ron Miller
(c) A. D. Fortes 2012
Facts about Titan
1.35 × 10^23 kg (1.8 Moons)
March 25, 1655
Titan’s diameter is 50 percent larger than Earth’s Moon, making it among the largest natural satellites in the solar system.
Titan’s most obvious feature is its heavy, hazy atmosphere. The most abundant gas is nitrogen, with methane and ethane clouds and a thick organic smog.
It was discovered in 1655 by Dutch astronomer Christiaan Huygens. It is named for mythological Titans, the brothers and sisters of the Greek god Cronus.
The composition of Titan is known to be water ice over a rocky interior. Its surface has liquid hydrocarbon lakes and the vents of cryovolcanoes, distributed among areas of bright and dark terrain that show evidence of some impact cratering.
Titan is thought to have several layers: a rocky core, surrounded by layers of crystalline ice. It is likely that the core is still hot, with a layer of liquid water and ammonia.
Like other moons around their primary planets, Titan has a rotation period that is the same as its orbital period. That means it turns on its axis in the same length of time as it takes to orbit Saturn.
Titan may have formed as material in orbit around early Saturn began to accrete. Giant impacts and collisions may have disturbed the orbits of Titan and other moons into their current positions.
Saturn's largest moon, Titan, is an icy world whose surface is completely obscured by a golden hazy atmosphere. Titan is the second largest moon in our solar system. Only Jupiter's moon Ganymede is larger, by just 2 percent. Titan is bigger than Earth's moon, and larger than even the planet Mercury.
This mammoth moon is the only moon in the solar system with a dense atmosphere, and it’s the only world besides Earth that has standing bodies of liquid, including rivers, lakes and seas, on its surface. Like Earth, Titan’s atmosphere is primarily nitrogen, plus a small amount of methane. It is the sole other place in the solar system known to have an earthlike cycle of liquids raining from clouds, flowing across its surface, filling lakes and seas, and evaporating back into the sky (akin to Earth’s water cycle). Titan is also thought to have a subsurface ocean of water.
Size and Distance
Titan has a radius of about 1,600 miles (2,575 kilometers), and is nearly 50 percent wider than Earth’s moon. Titan is about 759,000 miles (1.2 million kilometers) from Saturn, which itself is about 886 million miles (1.4 billion kilometers) from the Sun, or about 9.5 astronomical units (AU). One AU is the distance from Earth to the Sun. Light from the Sun takes about 80 minutes to reach Titan; because of the distance, sunlight is about 100 times fainter at Saturn and Titan than at Earth.
Orbit and Rotation
Titan takes 15 days and 22 hours to complete a full orbit of Saturn. Titan is also tidally locked in synchronous rotation with Saturn, meaning that, like Earth’s Moon, Titan always shows the same face to the planet as it orbits. Saturn takes about 29 Earth years to orbit the Sun (a Saturnian year), and Saturn’s axis of rotation is tilted like Earth’s, resulting in seasons. But Saturn’s longer year produces seasons that each last more than seven Earth years. Since Titan orbits roughly along Saturn’s equatorial plane, and Titan’s tilt relative to the sun is about the same as Saturn’s, Titan’s seasons are on the same schedule as Saturn’s—seasons that last more than seven Earth years, and a year that lasts 29 Earth years.
Scientists aren’t certain about Titan’s origin. However, its atmosphere provides a clue. Several instruments on the NASA and ESA Cassini-Huygens mission measured the isotopes nitrogen-14 and nitrogen-15 in Titan’s atmosphere. The instruments found Titan’s nitrogen isotope ratio most resembles that found in comets from the Oort Cloud—a sphere of hundreds of billions of icy bodies thought to orbit the Sun at a distance between 5,000 and 100,000 astronomical units from the Sun (Earth is about one astronomical unit from the Sun—roughly 93 million miles or 150 million kilometers). Titan’s atmospheric nitrogen ratio suggests the moon’s building blocks formed early in the solar system's history, in the same cold disk of gas and dust that formed the Sun (called the protosolar nebula), rather than forming in the warmer disk of material that Saturn later formed from (called the Saturn sub-nebula).
Titan’s internal structure isn’t entirely known, but one model based on data from the Cassini-Huygens mission suggests Titan has five primary layers. The innermost layer is a core of rock (specifically, water-bearing silicate rock) about 2,500 miles (4,000 kilometers) in diameter. Surrounding the core is a shell of water ice—a special type called ice-VI that is only found at extremely high-pressures. The high-pressure ice is surrounded by a layer of salty liquid water, on top of which sits an outer crust of water ice. This surface is coated with organic molecules that have rained or otherwise settled out of the atmosphere in the form of sands and liquids. The surface is hugged by a dense atmosphere.
The surface of Titan is one of the most Earthlike places in the solar system, albeit at vastly colder temperatures and with different chemistry. Here it is so cold (-290 degrees Fahrenheit or -179 degrees Celsius) that water ice plays the role of rock. Titan may have volcanic activity as well, but with liquid water “lava” instead of molten rock. Titan’s surface is sculpted by flowing methane and ethane, which carves river channels and fills great lakes with liquid natural gas. No other world in the solar system, aside from Earth, has that kind of liquid activity on its surface. Vast regions of dark dunes stretch across Titan’s landscape, primarily around the equatorial regions. The "sand" in these dunes is composed of dark hydrocarbon grains thought to look something like coffee grounds. In appearance, the tall, linear dunes are not unlike those seen in the desert of Namibia in Africa. Titan has few visible impact craters, meaning its surface must be relatively young and some combination of processes erases evidence of impacts over time. Earth is similar in that respect as well; craters on our planet are erased by the relentless forces of flowing liquid (water, in Earth's case), wind, and the recycling of the crust via plate tectonics. These forces are present on Titan as well, in modified forms. In particular, tectonic forces—the movement of the ground due to pressures from beneath—appear to be at work on the icy moon, although scientists do not see evidence of plates like on Earth.
Our solar system is home to more than 150 moons, but Titan is unique in being the only moon with a thick atmosphere. At the surface of Titan, the atmospheric pressure is about 60 percent greater than on Earth—roughly the same pressure a person would feel swimming about 50 feet (15 meters) below the surface in theocean on Earth. Because Titan is less massive than Earth, its gravity doesn't hold onto its gaseous envelope as tightly, so the atmosphere extends to an altitude 10 times higher than Earth's—nearly 370 miles (600 kilometers) into space. Titan's atmosphere is mostly nitrogen (about 95 percent) and methane (about 5 percent), with small amounts of other carbon-rich compounds. High in Titan’s atmosphere, methane and nitrogen molecules are split apart by the Sun's ultraviolet light and by high-energy particles accelerated in Saturn's magnetic field. The pieces of these molecules recombine to form a variety of organic chemicals (substances that contain carbon and hydrogen), and often include nitrogen, oxygen and other elements important to life on Earth. Some of the compounds produced by that splitting and recycling of methane and nitrogen create a kind of smog—a thick, orange-colored haze that makes the moon's surface difficult to view from space. (Spacecraft and telescopes can, however, see through the haze at certain wavelengths of light outside of those visible to human eyes.) Some of the heavy, carbon-rich compounds settle to the moon’s surface—these hydrocarbons play the role of “sand” in Titan’s vast dune fields. And methane condenses into clouds that occasionally drench the surface in methane storms. The methane in Titan’s atmosphere is what makes its complex atmospheric chemistry possible, but where all that methane comes from is a mystery. Because sunlight continuously breaks down methane in Titan’s atmosphere, some source must be replenishing it or it would be depleted over time. Researchers suspect methane could be belched into Titan's atmosphere by cryovolcanism—volcanoes releasing chilled water instead of molten rock lava—but they’re not certain if this or some other process is responsible.
Few worlds in our solar system are as compelling as Saturn’s icy ocean moon Enceladus. A handful of worlds are thought to have liquid water oceans beneath their frozen shell, but Enceladus sprays its ocean out into space where a spacecraft can sample it. From these samples, scientists have determined that Enceladus has most of the chemical ingredients needed for life, and likely has hydrothermal vents spewing out hot, mineral-rich water into its ocean.
About as wide as Arizona, Enceladus also has the whitest, most reflective surface in the solar system. The moon creates a ring of its own as it orbits Saturn—its spray of icy particles spreads out into the space around its orbit, circling the planet to form Saturn’s E ring.
Enceladus is named after a giant in Greek mythology.
Pictures from the Voyager spacecraft in the 1980s indicated that although this moon is small—only about 310 miles (500 kilometers) across — its icy surface is remarkably smooth in some places, and bright white all over. In fact, Enceladus is the most reflective body in the solar system. For decades, scientists didn’t know why.
Because Enceladus reflects so much sunlight, the surface temperature is extremely cold, about minus 330 degrees Fahrenheit (minus 201 degrees Celsius). But it is not as cold and inactive a place as it appears.
About as wide as Arizona, Enceladus orbits Saturn at a distance of 148,000 miles (238,000 kilometers) between the orbits of two other moons, Mimas and Tethys. Enceladus is tidally locked with Saturn, keeping the same face toward the planet. It completes one orbit every 32.9 hours within the densest part of Saturn's E Ring. Also, like some other moons in the extensive systems of the giant planets, Enceladus is trapped in what’s called an orbital resonance, which is when two or more moons line up with their parent planet at regular intervals and interact gravitationally. Enceladus orbits Saturn twice every time Dione, a larger moon, orbits once. Dione’s gravity stretches Enceladus’ orbit into an elliptical shape, so Enceladus is sometimes closer and other times farther from Saturn, causing tidal heating within the moon.
Parts of Enceladus show craters up to 22 miles (35 kilometers) in diameter, while other regions have few craters, indicating major resurfacing events in the geologically recent past. In particular, the south polar region of Enceladus is almost entirely free of impact craters. The area is also littered with house-sized ice boulders and regions carved by tectonic patterns unique to this region of the moon.
In 2005, NASA’s Cassini spacecraft discovered that icy water particles and gas gush from the moon’s surface at approximately 800 miles per hour (400 meters per second). The eruptions appear to be continuous, generating an enormous halo of fine ice dust around Enceladus, which supplies material to Saturn's E-ring. Only a small fraction of the material ends up in the ring, however, with most of it falling like snow back to the moon’s surface, which helps keep Enceladus bright white.
The water jets come from relatively warm fractures in the crust, which scientists informally call the “tiger stripes.” Several gases, including water vapor, carbon dioxide, methane, perhaps a little ammonia and either carbon monoxide or nitrogen gas make up the gaseous envelope of the plume, along with salts and silica. And the density of organic materials in the plume was about 20 times denser than scientists expected.
From gravity measurements based on the Doppler effect and the magnitude of the moon’s very slight wobble as it orbits Saturn, scientists determined that the jets were being supplied by a global ocean inside the moon. Scientists think that the moon’s ice shell may be as thin as half a mile to 3 miles (1 to 5 kilometers) at the south pole. The average global thickness of the ice is thought to be about 12 to 16 miles (20 to 25 kilometers).
Since the ocean in Enceladus supplies the jets, and the jets produce Saturn’s E ring, to study material in the E ring is to study Enceladus’ ocean. The E ring is mostly made of ice droplets, but among them are peculiar nanograins of silica, which can only be generated where liquid water and rock interact at temperatures above about 200 degrees Fahrenheit (90 degrees Celsius). This, among other evidence, points to hydrothermal vents deep beneath Enceladus’ icy shell, not unlike the hydrothermal vents that dot Earth’s ocean floor.
With its global ocean, unique chemistry and internal heat, Enceladus has become a promising lead in our search for worlds where life could exist.
British astronomer William Herschel spotted Enceladus orbiting Saturn on 28 August 1789.
Enceladus is the sixth-largest moon of Saturn and, after Titan, one of the most-studied worlds in the system. It was discovered in 1789 by William Herschel and named after the Greek mythological giant Enceladus.
1.08 × 10^20 kg (0.1% Moon)
August 28, 1789
Enceladus was first studied in detail by the Voyager spacecraft. The Cassini mission did close flybys of this moon, to map its surface in high resolution.
Enceladus is a largely icy world with some percentage of its mass being silicates. It appears to have a rocky core mixed with water ice, and a frozen mantle.
Cryovolcanic activity in Enceladus is sending geysers of water ice particles out from underneath the surface. The Cassini spacecraft has imaged these geysers spouting from so-called “tiger stripes” vent areas on this moon.
The icy particles from Enceladus spread out to space and feed the nearby E-ring with material.
The volcanic action on Enceladus led scientists to suggest that a liquid water ocean lies under the surface of this moon, and is feeding the geysers seen by Cassini.
Enceladus is thought to be heated from within by either radioactive heating (the decay of radioactive elements in the core) or tidal flexing as Saturn’s immense gravity pulls on the moon.
Future missions have been proposed to explore Enceladus and perhaps bring back samples of its icy plume material. These would also study the other moons of Saturn, plus the ring system.
As with Europa at Jupiter, scientists suspect that Enceladus could be a habitable world to some forms of life. There is no proof of life there, but future missions could test for life signs.