What is the name of the fourth largest satellite of Jupiter. The largest satellites of Jupiter. Size matters
Europa rising, captured by the Cassini spacecraft.
To date, about 180 planetary satellites have been discovered in the Solar System. The development of astronomy, as well as the use of interplanetary aircraft to explore outer space, makes it possible to detect celestial bodies of ever smaller size in it, so this figure is constantly increasing. More than half of the discovered satellites are satellites of Jupiter, the largest planet orbiting the Sun.
Today their number is estimated at 79, but it is quite arbitrary and scientists say that in fact there are at least a hundred of them. 50 satellites already have their own names - according to tradition, they are called female names in honor of the lovers and numerous daughters of Jupiter (Zeus). In ancient times, deities were not particularly moral and discriminating, so among the satellites of Jupiter there was also Ganymede, a beautiful young man who liked the almighty thunderer and was therefore kidnapped by him. The remaining 29 celestial bodies, discovered relatively recently, do not yet have proper names.
The role of Jupiter's satellites in the development of astronomy
Pictured from left to right are Ganymede, Callisto, Io and Europa. These satellites are among the largest in the solar system and can be observed with a small telescope.
Jupiter became the first planet in the solar system to have satellites discovered, not counting the Moon, a satellite of the Earth. This was done by Galileo Galilei, who in 1610, using a telescope, discovered small stars next to the giant that behaved unusually compared to other celestial objects. After observing their movements for several days, he realized that they revolved around Jupiter, which means they were not independent planets, but its satellites. This is how Ganymede, Europa, Io and Callisto were discovered.
Measuring the speed of light
In the 17th century, scientists did not have an accurate idea of the finite speed of light, so it was important to experimentally find out how it propagates - instantly or not. Jupiter's moons were able to help solve this problem. If light waves from any sources propagated instantly, then the location of celestial bodies in the sky recorded by an observer would completely correspond to the actual one. If this radiation has a finite speed, then the real picture will be distorted due to the different distances of the objects in question.
In 1675, the Dane Ole Roemer calculated the location of Jupiter's satellites for two cases: the first - the Earth and the gas giant are on the same side of the Sun, the second - on different sides. Having identified discrepancies between calculations and observations, he came to the correct conclusion that the speed of light has a finite value, but could not accurately calculate it due to the lack of accurate data at that time on the distance of the orbits of the Earth and Jupiter from the Sun.
Failed star
Jupiter, processed image from Voyager 1 probe
The gas giant has formed its own mini-structure within the Solar System with numerous satellites of various sizes orbiting around it. This fact, the chemical composition of its atmosphere (hydrogen and helium), as well as its truly impressive size, allow us to call Jupiter a failed star. However, its mass is not enough for a thermonuclear reaction to occur, which means it will never be able to become one. But if Jupiter were an order of magnitude heavier, then there would be not one luminary in the Solar System, but two - researchers of the Universe know brown dwarfs that have a mass approximately 12-80 times greater than that of the largest planet in the Solar System, which are among the lightest "weight category" of stars.
Jupiter Energy
A study of the largest planet in the solar system showed that it emits about 2.5 times more energy than it receives from the outside, which indicates the presence of some internal sources of this phenomenon. Moreover, Jupiter’s radiation is in a very wide wavelength range, including the visible spectrum.
A generally accepted explanation for this fact has not yet been found. It is assumed that the processes of phase transition of metallic hydrogen into the molecular phase can serve as energy sources. Also, most researchers agree that the planet’s core is heated due to internal compression and has a temperature, according to various sources, from 20,000°C to 30,000°C.
Classification of Jupiter's satellites
If a planet has many satellites, then for the sake of convenience they are usually divided into three main groups: main, internal and external. The main satellites mean the largest satellites, of which Jupiter has four: Ganymede, Europa, Io and Callisto. They are also often called “Galilean”, in honor of the Italian astronomer who discovered them. The regions of space around the central planet are divided, in relation to the orbits of the main satellites, into inner and outer regions. Depending on which of these parts of space any other satellite is located, it has a name: “internal” or “external”.
The inner satellites are much smaller than the Galilean ones and rotate in orbits 1.8-3.1 radii of Jupiter, that is, very close to its conventional surface.
The main satellites are located somewhat further away, occupying a ring 20 radii wide of the planet, while the closest of them, Io, is located six radii from the center of rotation. The internal and main celestial bodies that make up Jupiter's retinue rotate in the equatorial plane.
External satellites are located at a distance of 2-50 million km from the center of the planet. Their dimensions are generally estimated at several kilometers, but there are several relatively large ones (the largest is 170 km). These celestial bodies usually have irregular shapes, elliptical orbits and varying inclinations to the equatorial plane.
Some of them rotate in the direction opposite to the rotation of the planet and other satellites. By calculation, it is possible to determine the region of gravitational attraction of any body (the so-called Hill sphere), which for Jupiter is about 50 million km. This is a possible limit for searching for satellites.
Jupiter has four internal satellites and all of them are located inside the orbit of Io, the closest Galilean satellite to the planet.
They are called Adrastea, Amalthea, Metis and Thebe. The largest of them - Amalthea - has an irregular shape, is heavily pitted with craters and in size (270x165x150 km) ranks fifth in the Jupiter system. Thebe is approximately half the size (116x98x84 km) and is shaped like an ellipsoid. The remaining two satellites - Adrastea and Metis - have dimensions of 25x20x15 km and 60x40x34 km, respectively.
All four small planets belong to the regular category, i.e. they rotate in the same direction as the main satellites, and their orbits are located in the equatorial plane and are close to circular.
Moving at almost the same distance from Jupiter, Metis and Adrastea are ahead of its rotation around its own axis, which leads to the emergence of tidal forces that inexorably bring them closer to the surface of the planet. Therefore, there is a very high probability that they will end up falling on her.
Amalthea
Amalthea
The most interesting of these satellites is Amalthea, discovered in 1892 by Edward Barnard. The dark red color of its surface has no analogues in the solar system. Recent studies have suggested that it consists mainly of ice with inclusions of minerals and sulfur-containing substances.
Such conclusions can be drawn from the low density of the celestial body (900 kg/m3) and data from the analysis of its radiation. But such a hypothesis does not explain the color of the satellite. If we take it as a basis, then we can talk about the extra-Jovian origin of this body, since an icy satellite could not form near the surface of Jupiter.
External satellites
External satellites, and currently there are 59 of them, are distinguished by a significantly greater spread of parameters and characteristics than those of the main and internal ones. All of them revolve in elliptical orbits with a large angle of inclination to the equatorial plane. All external satellites that were able to be observed by spacecraft flying past visually resemble shapeless blocks with a surface corroded by travel.
They can be classified according to the values of the semimajor axis and the angle of inclination of rotation to the plane of Jupiter's equator, as well as its direction. Some of the satellites move in very close orbits and, apparently, are pieces of a larger celestial body that was destroyed as a result of a collision with another space object. Closer to the planet there are satellites rotating in the same direction as the main ones.
Irregular satellites
Next are satellites with reverse motion. They are divided into groups: Ananke, Karme, Himalia and Pasipha. In each of these families, one large (size more than 14 km) and a number of small (less than 4 km) bodies are distinguished.
The similarity of the motion trajectories most likely indicates the common origin of the satellites of the same group, which is further confirmed by the analysis of their speeds, which differ insignificantly from each other. A number of satellites have not yet been classified and are awaiting their researchers.
The study of celestial bodies orbiting in the distant outer orbits of Jupiter is interesting because they have undergone little change since their formation and therefore carry information about the nature of the solar system.
Most likely, some of them flew freely in outer space from other regions of the galaxy and were captured by the gravitational field of the giant planet. Therefore, analysis of their chemical composition will allow us to learn more not only about Jupiter and its satellites, but also about the structure of the Universe as a whole.
Main (Galilean) satellites
Crescent planets and largest satellites of the solar system
The main satellites of Jupiter were formed simultaneously with it and have orbits close to circular. They rotate in the plane of the equator at a distance from 420 thousand km to almost 2 million km from the center of the planet’s core. There are four such satellites in the gas giant system. Their names, in order of distance from the planet, are Io, Europa, Ganymede and Callisto. The density of the structure of these satellites depends on the distance from the planet. The closer a satellite is to Jupiter, the greater the specific gravity of the material from which it consists. So Io has a density of 3530 kg/m3, and Callisto has a density of 1830 kg/m3. All these celestial bodies, like the Moon in relation to the Earth, always face their planet with one side.
All of Jupiter’s satellites are at least one and a half times larger than the Moon, and Ganymede, the largest satellite of the Solar System, exceeds the size of its smallest planet, Mercury, by 8% (in diameter). True, due to its low density (1936 kg/m3;) it is more than twice as massive as this planet. Scientists believe that earlier there were more main satellites, and they all formed from one gas and dust cloud. Subsequently, some of them, under the influence of gravitational forces, fell to the surface of Jupiter, and only four remained, observed today.
Some features of the Galilean satellites
Close and long-term study by astronomers from many countries, as well as several interplanetary space missions that transmitted their observations to Earth, made it possible to obtain a lot of interesting data about the main satellites of Jupiter.
And about
Io is the most volcanically active celestial body in the Solar System. The proximity of massive Jupiter leads to fracture of the surface of the satellite and activation of sulfur emissions, giving it an orange-yellow color. Most likely, its surface consists of a mixture of ice and rocks.
Europe
Europa is completely covered in a crust of water ice, which may conceal a liquid ocean that is more than twice the volume of water on Earth. Moreover, in photographic images the surface of the satellite has a mesh structure, which suggests the presence of faults, cracks and thawed patches. It is assumed that water is also present on Ganymede and Callisto. Europa may have twice as much water as Earth. Again, the planet's gravity is thought to heat up the interior and keep it warm.
Ganymede is the largest moon, larger than the planet Mercury. It is the only one in the solar system that has its own magnetic field.
Callisto, the fourth moon, has one of the most densely cratered surfaces. Unlike the others, Callisto's surface is very ancient, with impact craters, billions of years old.
Answer from Yerenga[guru]
Ganymede (ancient Greek Γανυμήδης) is the seventh satellite of Jupiter in its outer orbit, one of the Galilean satellites. It is the largest satellite in the Solar System, 8% larger than Mercury (the diameter of Ganymede is 5,268 kilometers), and almost twice as massive as this planet - 45%. By comparison, Ganymede's diameter is 2% larger than that of Titan, the second largest moon in the Solar System, and it also has the highest mass of any planetary moon, with a mass 2.02 times that of Earth's Moon. Orbiting in about seven days, Ganymede participates in a 1:2:4 orbital resonance with Jupiter's other moons Europa and Io. Ganymede consists of approximately equal amounts of silicate rocks and water ice. It is a fully differentiated body with a liquid core rich in iron. The subsurface ocean on Ganymede is believed to exist between layers of ice beneath the surface, extending approximately 200 kilometers deep. The surface of Ganymede itself is represented by two types of surface landscapes. The dark areas, which occupy a third of the moon's surface, are dotted with impact craters that are up to four billion years old. The light areas covering the rest of the area are rich in extensive depressions and ridges that are somewhat younger in age. The cause of the destroyed geology of the light areas is not fully understood, but is likely the result of tectonic activity caused by periodic heating. Ganymede is the only moon in the Solar System with its own magnetosphere, which was most likely created by convection in a liquid, iron-rich core. The small magnetosphere is contained within Jupiter's much larger magnetic field and is connected to it through "open" field lines. The satellite also has a thin oxygen atmosphere, which includes O, O2 and possibly O3 (ozone). Atomic hydrogen is found in the atmosphere in small quantities. The connection between the satellite's ionosphere and the atmosphere is currently unclear. The discovery of Ganymede belongs to Galileo Galilei, who first saw it on January 7, 1610. The name was soon proposed by Simon Marius in honor of the mythological Ganymede - the ancient Greek god of the cupbearer, lover of Zeus. The study of Ganymede by spacecraft began with the study of the Jupiter system by Pioneer 10. The Voyager program carried out more advanced studies of Ganymede and managed to get an idea of its size. The underground ocean and magnetic field were discovered by the Galileo spacecraft. A new mission to study Jupiter's icy moons, JUICE, was approved by ESA on May 3, 2012, and is scheduled to launch in 2022 and arrive in the Jupiter system in 2030.
Jupiter is an amazing planet in many ways: The largest planet in the solar system, it has the largest mass, because of this the gravitational force of the planet is simply enormous, this planet, like Saturn, has a distinctive feature -; These are not all the characteristics of Jupiter, but this time I will talk about one of them - its satellite. Jupiter's largest satellite is Ganymede.
Its size allows it to hold 67 satellites in its orbits, but one of the most interesting is Ganymede. Ganymede is not only the largest moon of Jupiter, it is also the largest in the entire solar system. Ganymede is part of the Galilean satellites (the first discovery and observation was made by Galileo Galilei in January 1610 using his first telescope). Ganymede is so large that it is larger than the planet Mercury (Ganymede's diameter is 5,267 km), but Ganymede's mass is about 45% of Mercury's mass.
The largest satellite of Jupiter also differs from all other satellites in that it has its own magnetosphere (magnetic field). Most likely, the magnetic field is caused by convention (a process in which the internal energy of a satellite from the core is transferred by flows to its surface) in the iron-rich core. In addition to the magnetosphere, the satellite also has an atmosphere consisting mainly of atomic oxygen (O), oxygen (O 2) and ozone (O 3). The atmosphere surrounds the satellite in a thin layer and is highly discharged, but, apparently, the satellite is able to hold it due to its gravitational force.
Ganymede and its closest moons
Ganymede, together with Europa and Io, are in orbital resonance; for every revolution of Ganymede around Jupiter, there are 2 revolutions around the planet by the satellite Europa and 4 by Io. Ganymede is very similar to Jupiter's moon Io in its structure - an outer layer of ice, about 800 km. Under this layer of ice, liquid water presumably exists; the water in this ocean may not freeze due to the suitable temperature of the satellite's core. 
The largest satellite of Jupiter. Studying
Over the entire period, the largest satellite of Jupiter was visited by 6 spacecraft: Pioneer 10, 11 (in 1973 and 1974, respectively) for the first time received images of Ganymede from close range, Voyager 1, 2 thanks to which the satellite was able to be photographed with higher image quality. Then, the largest satellite of Jupiter was visited by the Galileo spacecraft, which discovered a magnetic field and an ocean on the satellite, under a layer of ice; the last one visited was the New Horizons spacecraft. Now the Juno spacecraft has entered Jupiter orbit, this was done on July 5, 2016. It will explore the origins of Jupiter, its atmosphere and, possibly, the probe will visit several moons, including Ganymede.
Jupiter is the largest planet in our star system, and like most giants, it has its own natural satellites. Currently, there are 79 of them known. Not all of them are interesting to study, some are huge boulders only a few kilometers in diameter, but the largest Moons of Jupiter are real planets. We will talk about them.
| N | Satellite | Opening year | Average radius(km) |
| 1 | 1610 | 2634 | |
| 2 | 1610 | 2410 | |
| 3 | 1610 | 1821 | |
| 4 | 1610 | 1560 | |
| 5 | 1904 | 85 | |
| 6 | 1892 | 83.4 | |
| 7 | 1980 | 49.3 | |
| 8 | 1905 | 43 | |
| 9 | 1908 | 29 | |
| 10 | 1979 | 21.5 | |
| 11 | 1914 | 19 | |
| 12 | 1938 | 18 | |
| 13 | 1951 | 14 | |
| 14 | 1974 | 10 | |
| 15 | 1979 | 10 |
It is the largest moon in the solar system and one of the moons discovered by Galileo back in 1610. Ganymede is located in the seventh orbit from the surface of Jupiter, its mass is slightly less than 1/2 the mass of Mercury, the orbital radius is 536,000 kilometers, and the average radius of the satellite itself is 2,634 kilometers. This cosmic body has its own magnetosphere. A third of the satellite is occupied by dark areas, on which there are many marks from meteorite craters. Lighter areas cover the rest of the surface, which astronomers believe are numerous ridges and plains.
Callisto is interesting because, like the Moon, it always revolves around Jupiter with one side facing it - the period of rotation around its axis is equal to the orbital one. The radius of the satellite is over 2,410 kilometers, which is approximately equal to the radius of Mercury. The surface includes ice and rocks (in approximately equal quantities). Spectroscopic analysis determined the concentration of carbon dioxide, water ice, as well as the presence of organic elements and silicates. The orbital eccentricity is 0.0074, the atmosphere is very rarefied, consists of carbon dioxide, and the possible presence of molecular hydrogen. Callisto's ionosphere is relatively powerful.
And about
Io is the closest satellite to Jupiter among those discovered by Galileo (the so-called Galilean satellites), and the third largest. The average radius of Io is over 1800, the average radius of the orbit is 421,700 kilometers. The orbital eccentricity is 0.0041. This is the most active body in the orbit of Jupiter from a geological point of view, and there is active volcanic activity here. The number of known active volcanoes on Io exceeds 400. In terms of its geometric dimensions, the satellite ranks fourth among all planetary satellites in the Solar System.
The smallest of Galileo's satellites has a radius of 1560 kilometers (in size it is inferior to our Moon). Europa, like the rest of the satellites of this group, was discovered in 1610. It is based on silicate rocks, with a presumably iron core in the center. The satellite has one of the smoothest surfaces of any celestial body in the Universe - it is mostly covered with ice and hard rock. There are few craters on the surface, but there are many cracks. For centuries, astronomers have been observing Europa using telescopes; since the last century, spacecraft have been used for research.
Himalia
The average radius of the satellite is 85 kilometers. The basis of its structure is presumably silicate rocks. The Himalia completely rotates around its axis in ten hours. The surface is very dark, the albedo is 0.04. The satellite makes a full revolution around the planet in 250 Earth days. The orbital eccentricity is about 0.16. Himalia was discovered in 1904 by D. Peiran, an astronomer at the Lix Observatory. It was given its current name in 1975; the satellite was named after the goddess Himalia. Studies of the satellite using spacecraft have been carried out already in this century.
The radius of this cosmic body is approximately 83 kilometers. The opening took place in 1892, on September 9. It was made by astronomer Eduard Bernard, who used a special refracting telescope. Amalthea was the last satellite to be discovered through visual observations, and also the first satellite of Jupiter to be discovered since the satellites of Galileo. The satellite is always turned to Jupiter with only one side, the radius of its complete orbit is approximately 2.54 from the orbit of Jupiter itself. The shape is irregular, has geometric characteristics of 250x146x128 kilometers. The craters are cup-shaped (due to low gravity on the surface).
The radius of the cosmic body does not exceed 49 kilometers. Like many other satellites, it has a synchronized rotation with Jupiter, which is why it always faces the same side towards it. It was discovered in 1979 by the American Voyager spacecraft. NASA astronomer Steven Sinnot was the first to look at it in photographs from Voyager. The orbital distance from the surface of Jupiter is 222,000 kilometers. Estimated weight 4.4 x 10 17 kilograms. The density and mass of the small planet are not known exactly.
Elara has a radius of 43 kilometers and was opened on January 2, 1905. The satellite received its current official name in 1975. The period of rotation around Jupiter is 259 days. The average distance from the surface of the gas giant is approximately 12,000,000 kilometers. According to the current assumption, the object consists of silicate rocks, the outer surface of the body is very dark, the albedo is 0.04, and the orbital eccentricity is considered to be 0.22.
The diameter of this space object is 29 kilometers, the semi-major axis of the orbit is 22,582,000 kilometers. The discovery of Pasiphe took place on January 27, 1908, by British astronomer Philibert Jacques of the Greenwich Observatory. The eccentricity of the satellite’s orbit is very large; it is usually classified as a separate group of satellites with similar parameters. Pasiphe is the largest satellite that has a reverse rotation direction, in addition, it is one of the largest irregular satellites.
The moon of Jupiter was discovered in 1979 and received its name four years later after the first wife of the god Zeus. The orbital radius is 128,000 kilometers, the average radius of the satellite itself is approximately 21.5 km. The shape is irregular - dimensions 60x40x32 km. This is the closest satellite to Jupiter, the orbit is within the main ring of the planet. Metis is completely free of dust, as it is located in the 500-kilometer gap of the main ring.
The satellite is classified as irregular and is characterized by retrograde motion. It was discovered in July 1914 by US astronomer Nicholson. It received its current name in 1975; from 1955 to 1975 it was called Hades, in honor of the nymph Sinope from ancient Greek mythology. The radius of the cosmic body is approximately 19 kilometers. Before the discovery in 1999-2000 of several satellites distant from Jupiter, it was the farthest from it.
Lysithea also has a second name - Jupiter X. The satellite was discovered in 1938, on July 6. The author was the American astronomer Nicholson. The object received its current name in 1975. The density of the cosmic body is 2.7 g/cm 3; the satellite makes a full revolution around the planet in more than 250 days. The distance from the surface of Jupiter is 11,717,000 kilometers, the radius of Lysithia is 18 kilometers. Presumably, it consists of silicate rocks. The surface of the satellite is very dark.
The surface radius of Ananke is 15 kilometers. It was opened in 1951, by the same Nicholson. The satellite is named after the character of Greek mythology - Ananke, the beloved of the god Zeus. Received its official "name" in 1975. It completes a full revolution around Jupiter in 630 Earth days. It is 22,000,000 kilometers away from the surface of the mother planet. The surface density was determined to be 2.8 g/cm 3 . This satellite gave a common name to a group of objects that orbit the gas giant and have similar parameters.
The diameter of the space object is 10 kilometers, it was discovered on September 14, 1974 by astronomer Charles Koval, representing the Palomar Observatory. The distance to the surface of Jupiter is over 11,165,000 kilometers, the average orbital period is 240 Earth days. Silicates are the basis of the structure of Leda. Been called by its current name since 1975.
The satellite moves directly in the rings of Jupiter, according to the existing assumption, it may be a source of material for the rings. The orbits of Merida and Adrastea are almost completely identical. The average radius of the satellite is approximately 10 kilometers, its mass is approximately 3x10 11 times less than the mass of Jupiter. Adrastea has a relatively high density, suggesting a high content of silicate rocks. The surface is dark in color; the satellite makes a full revolution around the planet in more than 7 hours of Earth time.
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