Natural satellites of Saturn

Saturn is the sixth in location from the Sun and the second in size (after the solar system. It is also called a gas giant, and it received its name in honor of agriculture.

It is difficult to give an exact answer to the question of how many moons Saturn has. Until 1997, astronomers knew only 18 of them. Nowadays, with the advent of the latest powerful telescopes, it has been possible to count many more of them. The natural satellites of Saturn are represented in a decent number (62 pieces - with a confirmed orbit). 53 of them have their own names. Most of them consist of ice, rocks and have no big sizes. This explains them main feature- high ability to reflect sunlight. In more large satellite x a stony core is formed. Most of them (except Phoebe and Hyperion) are constantly turned to the planet with only one side.

Saturn's satellites are either regular or irregular. There are 24 of the former, and 38 of the latter. The movement of regular satellites occurs in almost circular orbits located near the equatorial plane of the planet. They rotate exclusively in the direction of Saturn's rotation. This indicates that the regular satellites of Saturn were formed in the gas and dust cloud that surrounded the planet during its inception.

Irregular representatives include planets whose movement differs from the universal rules. They may have a more elongated orbit or eccentricity, a backward orbital motion, or a greater inclination toward the equatorial plane. The irregular satellites of Saturn, according to the characteristics of their orbits, are classified into 3 groups:

• Gali;
• Inuit;
• and Norwegian.

They rotate in chaotic orbits at a far distance from the planet. This indicates that Saturn recently captured these bodies from passing comet or asteroid nuclei.

Saturn's largest moon is Titan. In the Solar System, it is the only one with a dense atmosphere, and in terms of size it occupies an honorable 2nd place. It can be viewed through a telescope, as it smaller than Earth only doubled. This is a very interesting thing that scientists have already managed to study quite well. Saturn's moon Titan has been discovered to have a composition that is believed to be very similar to the Earth's early composition. Scientists express the opinion that processes that were characteristic of our planet billions of years ago are also taking place in its atmosphere.

Because of its opaque gaseous shell, which is about 300 km thick, it was virtually inaccessible to astronomers trying to measure its diameter. Only with the advent of recent advances in telescopic technology have studies shown that Titan's interior may consist of equal parts frozen water and solid rock. Its atmosphere is mainly formed of nitrogen, which makes it similar to Earth.

Previously, there was a hypothesis, which has not yet become obsolete, about the existence on this satellite of rivers, lakes and seas formed from methane or ethane. Methane is able to exist in three phases and maintain something similar to what is observed on this satellite.

Titan does not, which means that it does not have a core that conducts current. The surface temperature is estimated at 95 Kelvin, and the pressure is one and a half times higher than on Earth. Low temperatures prevent the formation of more complex organic substances. However, it has its own magnetic tail, formed from interaction with magnetic field Saturn, in whose magnetosphere Titan serves as a source of charged and neutral hydrogen atoms.

When studying the question of how many moons Saturn has, it is probably most accurate to consider the largest ones. One of them is Mimos, which has a huge crater called Herschel, which is about 130 km in diameter. This is larger than the size of many of Saturn's moons. Dione, Tethys, Enceladus and Rhea - all of them belong to large objects and have deep craters and canyons, and Enceladus is also the brightest celestial body in the solar system.

Saturn continues the list of giant planets. It is the sixth planet from the Sun in the Solar System, next to Jupiter. In addition, Saturn is the second largest planet in the solar system, second in size only to Jupiter, and the most distant of the planets that are visible from Earth with the naked eye.

Characteristics of Saturn

average orbital radius: 1,429,400,000 km
diameter: 120.536 km
weight: 5.68*10^26 kg

Saturn is far from the Sun - almost 10 times further than Earth, at a distance of more than a billion kilometers. It travels its orbital distance in 29.46 years. Saturn is approximately 9 times the size more than Earth and 95 times its mass. Just like Jupiter, it consists mainly of light gases - hydrogen and helium, which causes its very low density, which is even less than the density of water - only 0.63 g / cubic meter. cm. Saturn rotates quickly around its axis (orbital period is about 10 hours), and, just like Jupiter, its rotation is faster in the equatorial region, and slower near the poles. Due to centrifugal forces, Saturn is noticeably flattened - its equatorial radius exceeds 60 thousand km, and its polar radius is only 54 thousand km.
Both in composition and internal structure Saturn is similar to Jupiter. There is, however, slightly less helium in the atmosphere of Saturn - 7%, and not 11%, like Jupiter, perhaps because denser helium sinks deeper into the planet more intensively compared to hydrogen. Just like on Jupiter, in the atmosphere of Saturn there are clouds consisting of ammonia, methane, water vapor, etc. Moreover, the cloud cover on Saturn is more powerful than on Jupiter. There are also winds in Saturn's atmosphere. strong winds and lightning discharges are observed. It is assumed that in the center of Saturn, as in the center of Jupiter, under the influence powerful pressure hydrogen goes into a special phase - the so-called. metallic hydrogen capable of conducting electricity. Circulations in the layer of metallic hydrogen create a magnetic field around Saturn, but it is much less powerful than that of Jupiter.

The most famous feature of Saturn is its rings. These rings are easily visible from Earth even with a small telescope. The rings of Saturn were discovered back in the 17th century. After the Voyager flights, rings similar to those of Saturn were discovered on all the giant planets, but on Saturn they are incomparably more powerful. It is known that the ring system of Saturn consists of three parts, between which there are gaps. The rings themselves consist of a large number of stone and ice fragments, the sizes of which range from the size of a speck of dust to several meters.

The surroundings of Saturn were studied during expeditions launched by NASA spacecraft, the first of which flew near Saturn, Pioneer 11, and subsequently photographs of Saturn and its moons were taken by Voyagers. The most significant recent results were obtained during the expedition of the Cassini spacecraft, which reached the vicinity of Saturn in 2004 and has been in its orbit for 4 years.

Saturn has a large number of satellites (about 60 are known today).

Saturn's moons

A significant part of Saturn's moons discovered in Lately, rotates at very large distances from the planet in a variety of orbits and were probably captured by Saturn's gravitational field from among passing asteroids or comets.

Characteristics of some of Saturn's moons

Most of Saturn's moons are low-density, apparently consisting mainly of ice. Photos of some satellites are shown below:

Iapetus and Enceladus

Rhea and Dione

The largest of Saturn's moons, one of the largest satellites in the Solar System and of greatest interest for study, is Titan.

Titan was discovered by Huygens back in the 17th century. The satellite is quite large in size (its diameter exceeds 5 thousand km, which is only slightly less than two times less than the diameter of the Earth), but has a low density. It is assumed that Titan consists of a rocky core covered with an icy shell.
Titan is the only one of all the moons in the solar system that has a dense atmosphere. At the surface of Titan, the atmospheric pressure is 1.5 times higher than on Earth. For the most part, Titan's atmosphere consists of nitrogen (about 90%), it also contains argon and a small proportion of methane and other gases. Perhaps Titan's atmosphere is similar in composition to that of Earth on early stages of its existence.
Saturn and Titan are very far from the Sun, and the temperature there is very low. On its surface it is only 90-100 K (about - 180 ° C). Cloud cover makes it difficult to see surface details from space. Therefore, the Cassini spacecraft, which was also designed to study Titan, had an extensive set of equipment, including radar, instruments for studying the infrared spectrum, and, most importantly, a landing module designed to land on the surface of the satellite. In January 2005, this module successfully landed on the surface of Titan and was able to transmit to Earth more accurate data on the composition of the atmosphere, temperature and pressure, as well as photographs of the surface of Titan from a low altitude and directly photos from the surface itself (see figure).

The resulting images gave scientists confirmation of previously stated assumptions that methane can exist on Titan in a liquid state and play a role similar to water on Earth, forming vast reservoirs and rivers; methane rain also appears to fall on Titan.

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Titanium

(Titan) Diameter: 5152 km. Orbital period around Saturn: 15.945 days. Titan is the largest moon of Saturn, and also the second largest moon in the Solar System after Jupiter's moon Ganymede. It is the only body in the solar system, other than the Earth, that has liquid on its surface. Titan is the only satellite of the planet that has a dense atmosphere. Titan's diameter is twice that of the Moon, while its mass is almost twice as large. It is also larger than Mercury, although it is inferior in mass. Titan's gravity is about one-seventh that of Earth.

Titan's surface is mostly composed of water ice and sedimentary organic matter. There is no a large number of mountains and craters, as well as several cryovolcanoes. Thick atmosphere, surrounding Titan, for a long time did not allow its surface to be seen. The Cassini-Huygens spacecraft, which flew past the satellite in 2005, was able to obtain data on its structure.

Titan's atmosphere consists mainly of nitrogen and small amounts of methane and ethane, which form clouds that produce liquid and possibly solid precipitation. As a result, there are methane-ethane lakes and rivers. The pressure is almost 1.5 times higher than the pressure of the earth's atmosphere. Surface temperature is about -170“ C.

Despite low temperature, Titan is juxtaposed with Earth in the early stages of development. At the same time, it is very likely that the simplest forms of life can exist on the satellite. Titan was discovered by Dutch astronomer Christiaan Huygens in 1655. It became the first known satellite of Saturn.

Iapetus

(Iapetus) Average radius: 734.5 km. Orbital period around Saturn: 79.32 days. Iapetus is the twenty-fourth moon of Saturn and the third largest. Its second name is Saturn VIII. A total of 62 satellites of this planet are known. This is one of the most unusual and mysterious satellites of the solar system. Its density is about 1.083 g/cm3, indicating that Iapetus must consist almost entirely of water ice. The surface of the satellite has two zones: light and dark - the so-called Cassini region, separated by an unusually clear boundary. The dark area has an albedo of 0.03-0.05, like soot. The bright side, located in the direction of the satellite's orbit, has a very high reflectivity, comparable to freshly fallen snow. Explorations of Iapetus by spacecraft have shown that the chemical composition of the material on the surface varies greatly, from water ice to organic materials. In December 2004, new images of Iapetus were obtained, showing an unusual ring-shaped mountain range encircling its equator. The height of the mountains reaches 13 km, width 20 km, length - almost 1300 km. This makes the satellite very similar to Walnut, consisting of two halves. The origin of the ridge is absolutely unclear; scientists only assume that it could have appeared as a result of compression of rocks or the breakthrough of material from the depths of the moon to its surface. Iapetus was discovered by astronomer Giovanni Cassini on October 25, 1671. Observing the satellite through a telescope, he concluded that Iapetus has a bright and dark side and is always turned to Saturn with the same side.

Rhea

(Rhea) Diameter: 1528.6 km. Orbital period around Saturn: 4.5 days. Rhea is Saturn's second largest moon and has long been known as Saturn's "fifth moon." Modern name for the satellite in 1847, it was proposed by John Herschel, the son of the outstanding English astronomer William Herschel. The remaining seven moons of Saturn known at that time, Herschel Jr. proposed to distinguish by the names of the titans - the brothers and sisters of Kronos or his analogue in Greek mythology- Saturn. Rhea is an icy body with an average density of 1.23 g/cm3. Such a low density indicates that the satellite must consist of one-third rock, with the rest being water ice. The acceleration of gravity on the satellite is 0.264 m/s2. Rhea in composition and geological history similar to Dione. Since the satellites face Saturn with one side, they have different trailing and leading hemispheres, which are always directed in the direction of the satellite's orbital movement. Rhea's leading hemisphere is covered with many craters and is uniformly light. The posterior hemisphere contains dark areas, as well as a network of bright thin stripes. Data from the Cassini spacecraft obtained in January 2006 showed that these are cliffs of mountain slopes. At the same time, it was established that the satellite has a thin oxygen atmosphere. Rhea was discovered by the Italian astronomer Giovanni Cassini in 1672, who named the 4 moons of Saturn he discovered, including Rhea, “the stars of Louis” in honor of King Louis XIV of France.

Tethys

(Tethys) Average radius: 531.1 km. Orbital period around Saturn: 1.8878 days. Tethys is a moon of Saturn that has long been known as the “third moon of Saturn” and was called Saturn III. It is an icy body similar to Dione or Rhea. The density of the moon is 0.97 g/cm3. This indicates that it consists mainly of ice. The surface of Tethys is dotted with numerous craters and faults. Two clearly stand out on the satellite different types areas: some have a large number of craters, while others predominantly contain dark stripes stretching across the surface for a considerable distance. There are few craters in these areas. This indicates their late education. In the western hemisphere of Tethys there is a giant crater “Odysseus”, reaching 400 km in diameter. It has a fairly flat topography without a ridge around its circumference and a high central mountain. This is explained by the sliding of plastic ice over geologically significant periods of time. Another feature of Tethys is the giant Ithaca Canyon, 100 km wide and up to 5 km deep, stretching three-quarters of the satellite’s equator, that is, almost 2000 km. It is believed that the canyon could have been formed when the substance of the satellite solidified or as a result of a powerful impact during the appearance of the Odysseus crater, when a brittle fracture of the ice crust formed on the opposite side of the satellite under the influence of a shock wave. Tethys was discovered by Giovanni Cassini in 1684 and was first included in the “Stars of Louis,” named after the king of France.

Diona

(Dione) Average diameter: 1123.4 km. Orbital period around Saturn: 2.7/day. Dione is a natural satellite of Saturn, which was one of the seven moons named by John Hershep after the titans - the siblings of Kronos or his counterpart in Greek mythology - Saturn. It has two co-orbital satellites - Elena and Polydeuces, with close orbits. Dione is very similar to Rhea, another moon of Saturn. They both have similar composition, surface reflectivity - albedo and surface characteristics. Both satellites have very different posterior and leading hemispheres. Satellites are always turned to Saturn with one side, so one of the hemispheres - the leading one - faces the direction of the satellite's orbital movement. Dione consists predominantly of water ice with a significant admixture of rocks in the inner layers. This is evidenced by measurements of the satellite's density. Dione's leading hemisphere is covered with many craters and is uniform in brightness. The posterior hemisphere contains dark areas, as well as numerous thin light stripes. This is a “web” of ice ridges and cliffs. Measurements made by the Cassini spacecraft showed that some of them are several hundred meters high. A number of stripes cross the craters, therefore the cliffs appeared later than them. Dione was discovered by Italian astronomer Giovanni Cassini in 1684. He named it and four other satellites of Saturn discovered by him “the stars of Louis” in honor of King Louis XIV of France. In astronomy, Dione has long been designated as the “fourth satellite of Saturn.”

Enceladus

(Enceladus) Average radius: 252.1 km. Orbital period around Saturn: 1.37 days.

Enceladus is the sixth largest moon of Saturn and the fourteenth largest moon in order of distance from it. It orbits the dense part of Saturn's E ring, the outer, extremely wide ring of Saturn, which is a diffuse disk of microscopic ice or dust particles. Enceladus is one of three bodies in the solar system, along with Io, a satellite of Jupiter, and Triton, a satellite of Neptune, on which active volcanic eruptions are observed. Analysis of volcanic gases leaving the surface suggests they originate from a subsurface liquid water ocean. Their unique chemical composition, in turn, makes Enceladus an important target for astrobiological research. It is also likely that matter leaving Enceladus enters Saturn's E ring. In 2011, NASA scientists at the Enceladus Focus Group Conference stated that it is "the most habitable place in the solar system outside of Earth in throughout its existence." The satellite began to be actively studied with the beginning of the Voyager program, within the framework of which the first close-up photographs of Enceladus were obtained. In 1980, the Voyager 1 spacecraft was the first to approach the moon, and in 1981, it was visited by the Voyager 2 spacecraft. In 2004, the Cassini spacecraft was launched into orbit around Saturn and transmitted detailed images of Enceladus to Earth. The satellite is named after the giant ancient greek mythology Enceladus. The name was suggested by William Herschel's son, John Herschel.

Mimas

(Mimas) Average radius: 198.3 km. Orbital period around Saturn: 0.94 days. Mimas is the seventh moon of Saturn that was discovered. It was discovered on September 17, 1789 by William Herschel, an outstanding English astronomer of German origin. He is responsible for the discovery of the planet Uranus, its two satellites - Titania and Oberon, as well as two satellites of Saturn and infrared radiation. To this we can add that he is the author of twenty-four symphonies. Mimas's density is only 1.15 g/cm3, indicating its composition is predominantly water ice and some rocks. Due to the effect of Saturn's tidal forces on the satellite, Mimas is not entirely spherical. Its long axis exceeds the short one by 10%, and the dimensions of the satellite are 418x392x383 km. The moon's orbit is almost perfectly circular. The average distance from it to the center of Saturn is about 185,520 km. Mimas has a huge impact crater, Herschel, with a diameter of 130 km, which is almost a third of the diameter of the satellite itself. The height of its walls is about 5 km, the greatest depth is 10 km. The central elevation has a height of 6 km above the crater floor. The impact of the crater likely created cracks on the opposite side of the moon. The surface of Mimas is dotted with small impact craters, none of which are comparable in scale to Herschel. To date, only 35 objects on the surface of the satellite have their own names. Images from the infrared camera of the Cassini spacecraft taken in 2009-2010 showed that the temperature on the surface of the satellite was -209 °C.

Hyperion

(Hiperion) Average radius: 270 km. Orbital period around Saturn: 21.276 days. Hyperion is a natural satellite of Saturn, which was discovered in 1848 by American astronomer William Bond and his son George. And before this, the independent discovery of the satellite was made by British astronomer William Lassell. The satellite was named after the titan Hyperion. It is the largest irregular and non-spherical object in the Solar System. Its dimensions are 410 x 260 x 220 km. In astronomy, Hyperon was long known as Saturn VII. Since the satellite revolves around Saturn in a highly elongated elliptical orbit and also has a shape that is far from spherical, it is believed that the length of the day on Hyperion is not constant. In addition, it is in orbital resonance with Titan: the ratio of the orbital periods of these satellites around Saturn is 4:3. Therefore, the unevenness of its circulation or the length of the day can vary by tens of percent over several weeks. The surface of Hyperion is heavily cratered and has a characteristic jagged outline. These are probably traces of catastrophic collisions with cosmic bodies. The color of the surface varies slightly, which apparently reflects differences in its composition. At the bottom of most craters, a dark substance was found, probably deposited on the surface after impacts. Hyperion's density is very low; it is likely that it consists of 60% water ice with a small admixture of rocks and metals. Moreover, up to 40 percent or even more of its internal volume can be voids. It also contains light materials: frozen methane or carbon dioxide.

Phoebe

(Phoebe) Average radius: 106.5 km. Rotation period: 0.386 days. Phoebe is a distant irregular satellite of Saturn, moving in the opposite direction in a highly elongated, inclined orbit. It probably formed in the Kuiper Belt and was captured by Saturn's gravity. This hypothesis allows us to explain the reverse direction of the satellite’s orbital motion. The Kuiper Belt is a region of the Solar System extending from the orbit of Neptune to a distance of 55 AU. e. and includes mainly small bodies, which consist mainly of volatile substances-ices, such as methane, ammonia, water. By astronomical standards, Phoebe is a very small space object; its dimensions are only 230x220x210 km. The density of the material is also low, only 1.6 g/cm3, which suggests that the moon consists mainly of ice. Phoebe's surface is very dark and hardly reflects light. Albedo is 0.06. In the interiors of some craters, lighter material, presumably ice, was found. The temperature on the surface of the moon reaches -198 °C. The size of the semi-major axis of the orbit is 12.96 million km. In June 2004, the Cassini spacecraft flew past the satellite and transmitted photographs of Phoebe to earth. It is noticeable from them that the landscapes of Phoebe are very different from the landscapes of other asteroids. The moon's surface is more similar to that of Triton and other objects that formed in the outer reaches of the Solar System, which are about 4 billion years old. Phoebe was discovered in 1899 by the outstanding American astronomer William Pickering. The satellite is named after the Titanide Phoebe from ancient Greek mythology.

Janus

(Janus) Average radius: 89.5 km. Orbital period around Saturn: 0.694 days. Janus, the inner satellite of Saturn, is remarkable in that it moves in an orbit that is only 50 km away from the orbit of another satellite of Saturn, Epimetheus. This distance is significantly smaller than the satellites’ own dimensions. Scientists suggest that at the early stage of the formation of the Saturn system, both satellites were a single body. In 1997, at the University of Miami, astrophysicists Laura Batt and Paul Devries calculated the trajectory of an unusual pair of satellites. They found that Epimetheus and Janus move independently in their orbits until the inner satellite, located closer to Saturn, approaches the outer one. After this, under the influence of gravitational forces, the inner satellite is pushed into a higher orbit, and the outer one moves to a closer one to Saturn. Thus they change orbits. This change of orbits occurs approximately once every four years. Apparently, both moons formed a single whole in the past and at the early stage of the formation of the Saturn system they split into two satellites. Janus has a very low density - lower than the density of water, about 0.64 g/cm3. This can only be explained by the fact that it is a porous body consisting mostly of ice. The dimensions of the moon are 203x185x152.6 km. Janus was discovered by French astronomer Audouin Dollfus in 1966. It got its name from the god Janus from ancient Roman mythology. The satellite has another designation as Saturn X.

Epimetheus

(Epimetheus) Average radius: 58.1 km. Orbital period around Saturn: 0.694 days. Epimetheus is an inner satellite of the planet Saturn, forming a pair with another satellite of the planet - Janus. It moves in an orbit only 50 km away from the orbit of its “partner”. Moreover, once every four years, when both bodies come closer, it changes places with it, moving either to the outer or the inner orbit. The last change of orbits by satellites occurred in 2010. In December 1966, French astronomer Audouin Dollfus observed a moon of Saturn, which he named Janus. Three days later, American astronomer Richard Walker also observed a satellite in the same orbit. Both scientists believed that this was the same satellite. Only twelve years later, in October 1978, American astronomers Stephen Larson and John Fontaine established that these were in fact two different objects. Subsequently, this conclusion was confirmed by the Voyager 1 spacecraft, transmitting clear images of the satellites to Earth. The dimensions of Epimetheus are 135x108x105 km. The very low density, less than the density of water, about 0.69 g/cm3, can be explained by the fact that the moon is a porous body, consisting mostly of ice. Epimetheus has several craters with a diameter of more than 30 km, as well as mountain ranges and canyons. In general, the surface of the satellite is quite heavily cratered. This may indicate his great age. The surface of the moon has a fairly high reflectivity of 0.73. The satellite is named after the character of ancient Greek mythology Epimetheus. It was originally named Saturn XI.

© Vladimir Kalanov,
website"Knowledge is power".

Dozens of satellites revolve around Saturn. Currently, 53 satellites are known to have names; about a dozen celestial bodies are “waiting” to receive their own names after confirming their flight trajectories for involvement in the satellite system of Saturn. The largest satellite, Titan, is described in detail in the previous section of our website (go to "").

The sizes of these satellites of Saturn are very different - from two tens of kilometers in diameter or at their largest cross-section to one and a half thousand kilometers.

Here are the four largest satellites that were discovered at the end of the 17th century by the Italian astronomer Cassini. We list them in order of increasing distance from the planet (the diameters of the satellites in kilometers are indicated in parentheses): Tethys (1048), Dione (1118), Rhea (1528) and Iapetus (1436). If Tethys orbits Saturn at a distance of about 295 thousand km, then the average distance from Iapetus to Saturn is more than 3.5 million km. Iapetus is considered an outer satellite, because its orbit is external to that of Titan.

In a regular telescope, only Titan is visible as a small disk; the other satellites look like bright dots. All satellites are turned to the planet with one side, just like the Moon is to the Earth.

Almost all satellite orbits are circular and their planes are parallel to the plane of Saturn's equator. The exception is the orbits of Iapetus and Phoebe, whose planes are inclined by 14.7° and 150°, respectively. Phoebe, the most distant of all the satellites we describe here, is the only satellite that orbits Saturn in the opposite direction to the movement of all the other satellites. It is possible that Phoebe is an asteroid caught in the gravitational field of Saturn.

We have already mentioned the influence of the peculiarities of the movement of Saturn’s satellites on maintaining the stability of the structure of its rings. A unique feature of the motion of Saturn’s satellites is that some of them have periods of revolution around the planet that correlate with each other as multiples. For example, the orbital period of Mimas is exactly half the orbital period of Tethys; Enceladus and Dione have the same ratio of orbital periods. The effective radii of the orbits of Tethys, Telesto and Calypso are the same, and accordingly the orbital periods of these satellites are the same. As a result of these features of the motion of the satellites, their total gravitational field, in interaction with the gravitational field of the planet, creates conditions for the retention and movement of the rings around Saturn.

The density of satellite matter is generally low, less than 1.5 g/cm³. Most likely, this is because the main component of their substance is ice. Presumably, the structure of the substance is as follows: 30-40% rocks and 60-70% ice.

Information from AMC

Analysis of information received from the AMS shows that the further the planets and their satellites are located from the Sun, the lower their density. In general, the density of Saturn's moons is lower and their ice content is higher than that of Jupiter's moons. the presence of ice in the depths of satellites under conditions of rising temperature leads to manifestations of geological activity: volcanism, geysers, etc.

One of the largest of this group of satellites is Iapetus, its diameter is 1436 km, and has a density almost equal to that of ice. The brightness of the hemisphere constantly facing Saturn is five times the brightness of Saturn. This feature was noted by Cassini at the end of the 17th century. The reverse hemisphere of Iapetus is darker, perhaps because it is exposed to substances with low reflectivity. According to one hypothesis, such a substance could be dust from the neighboring planet Phoebe. True, this neighborhood is not very close: the effective radius of Phoebe’s orbit is almost nine and a half million kilometers greater than that of Iapetus.

The surface of Rhea, the second largest satellite of Saturn after Titan, is covered with numerous craters and resembles flat areas on the surface of the Moon. The sizes of the craters vary: there are a lot of small craters, but there are also large ones - from 30 to 100 km in diameter.

The satellite Dione, whose diameter is 1118 km, has the highest (after Titan) density of matter. Each side of the satellite has its own characteristics in surface morphology. On one side, craters with a diameter of 50 to 100 km are visible, intersecting with light stripes. On the other side, the stripes are not visible, the surface brightness is uniform, and flat areas with a small number of craters are visible.

Saturn's sixth largest moon, Enceladus, discovered in 1789 by Herschel, has the highest albedo of any moon in the entire solar system. The Cassini spacecraft got a good look at the moon Enceladus when it passed just 50 km from its surface on August 11, 2008. The device flew through clouds of ice particles emitted by geysers in the area south pole satellite On Earth, geysers emit boiling water and steam. The word "geyser" comes from the German "heiß" ("hot"). Geysers on Enceladus are completely different from those on Earth.

In July 2009, detailed data on chemical composition water
emissions from Enceladus geysers, confirming the theory of the liquid ocean as a source of water emissions.

There are volcanoes on Enceladus. But these volcanoes are unusual: not hot lava erupts from them, but pieces of ice along with steam. The appearance of the volcanoes is also unusual: these are numerous faults in the ice surface. Along the edges of the faults there are extensive deposits of ice particles of varying dispersion. The activity of geysers and volcanoes on Enceladus is explained by tidal forces acting on the satellite from Saturn.

The probe managed to capture several fountains up to 500 kilometers high. Scientists have even suggested that it is the geysers of Enceladus that feed one of Saturn’s rings, the E ring, with matter. Obviously, the processes that feed the ice geysers must be very powerful.

Of the other satellites of Saturn, we note Mimas, which has a huge impact crater equal to almost a third of the satellite’s diameter. The crater is named after William Herschel, who discovered Mimas in 1789. Without a doubt, the Herschel crater is a trace of a powerful blow received by the satellite during a collision with some celestial body. How Mimas survived such a blow remains a mystery.

© Vladimir Kalanov,
"Knowledge is power"

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