Ganymede area. How the moon Ganymede was discovered

Satellite of Jupiter Ganymede- the largest satellite not only of this planet, but of the entire solar system. It is so large that it exceeds the planet in size, and it is also the only planetary satellite that boasts the presence of a magnetosphere and, albeit a weak, but still oxygen atmosphere!

Ganymede is the most large satellite Jupiter

How the moon Ganymede was discovered

"Officially" Ganymede was discovered Galileo Galilei On January 7, 1610, and it was discovered purely by chance - while observing, the astronomer drew attention to four small "stars" next to him, and, noticing their shift the next night, made the correct assumption that there were no stars in front of him, but the moons of Jupiter. Galileo did not bother with the names and christened all the newly discovered celestial bodies (Callisto, Europa, Io, Ganymede) in a simple way: Jupiter 1, 2, 3 and 4.

Ganymede appeared in this list as "Jupiter 3".

However, here a German astronomer entered the scene Simon Mari, who claimed that he observed the satellites of Jupiter as early as 1609, and thought in advance to give them much more sonorous and interesting names. That's how the name came about Ganymede- in Greek myths this name was borne by the son of the Trojan king Rope, raised by Zeus (Jupiter) to heaven and included in his retinue.

However, this name came into wide use only in the 20th century.

Dimensions, landscape and surface composition of Ganymede

Ganymede is the largest moon in the solar system, with a diameter of 5268 kilometers and a record mass for planetary satellites of 1.4619 x 1023 (2 of our moons). Judging by the characteristics of the density of the substance that makes up its mass, Ganymede consists of approximately equal proportions of rock and water ice. The poles have ice caps made of water ice.

Ganymede makes a revolution around Jupiter in 7 days and 3 hours, and the average distance from Jupiter for this satellite is 1,070,400 kilometers.

Inside, the satellite has a liquid iron core, a silicate mantle, and a shell of ice. The core has a radius of 500 km, and its temperature is 1500-1700 K with a pressure of 10 Pa.

The mantle is represented by chondrites and iron. The outer ice crust of Ganymede has a thickness of up to 800 km, with a high probability it can be argued that a liquid ocean is located under the surface of this satellite of Jupiter.

On the surface of the satellite, two pronounced types of relief are distinguished. The first is ancient areas covered with craters (dark) occupying 1/3 of the surface, the second is young territories with ridges and "ravines" (light).

The young landscape is formed by tectonics, but, of course, of a different nature than on Earth. The cause of the formation of mountain ranges and chasms on Ganymede is cryovolcanism (eruption of ice volcanoes) and tidal heating.

The abundance of craters on the "ancient" flat areas of the planet is attributed to the period 3.5-4 billion years ago, when Ganymede was subjected to a powerful asteroid attack.

The landscape of Ganymede is quite bizarre, here and there it is crossed by wide strips, as if a giant skating rink had passed through them. In fact, these are areas of compression-tension of the surface

Atmosphere and magnetosphere of Ganymede

As already noted, it is Ganymede that has something that not all the planets of the solar system can boast of - it is highly discharged, but still oxygen atmosphere. Oxygen appears in it due to the presence of water ice deposits on the surface of the satellite, under the influence of ultraviolet radiation decomposing into hydrogen and oxygen. Moreover, since ozone was also found in the atmosphere of Ganymede, it is most likely that the satellite also has an ionosphere.

The presence of an atmosphere (or rather, the presence of atomic hydrogen in it) leads to airbrush effect- weak light radiation appearing at the poles of the planet.

However, although the phrase "oxygen atmosphere" sounds very nice and suggests colonization and extraterrestrial intelligence, it is worth remembering that the pressure of the atmosphere of Ganymede is only 0.1 Pa, that is, an insignificant part of the earth's.

Even more interesting feature this Jovian moon is the magnetosphere. Yes, Ganymede has a magnetosphere, the magnitude of the stable magnetic moment which reaches - 1.3 x 10 3 T m 3 (i.e. 3 times higher than that of Mercury). Strength magnetic field reaches 719 Tesla, and the diameter of the magnetosphere reaches 13156 km. Closed field lines are below 30° latitude, where charged particles are captured and form radiation belt. Among the ions, single ionized oxygen is the most common.

When the magnetosphere of Ganymede and the plasma of Jupiter come into contact, a situation is observed very similar to the contact solar wind and the earth's magnetosphere. However, it must be admitted that the satellite's magnetic field is too weak and unable to contain the radiation fluxes emitted by Jupiter, so if we were on the surface of Ganymede, despite the presence of the magnetosphere, we would not be in trouble.

The structure of the big moon Jupiter - Ganymede

The study of Ganymede in our time and the prospects for the colonization of Jupiter's moon

AT modern times several research probes were sent to Jupiter, so we have fairly detailed data not only about the giant planet, but also about its satellites.

The spacecraft Pioneer 10 (1973) and Pioneer 11 (1974) gave us insight into the physical characteristics of Jupiter's moons, Voyager 1 and Voyager 2 (1979) supplied photographs and " atmospheric samples, "but these devices rather asked questions ...

The Galileo probe, which studied Ganymede from 1996-2000, began to give answers. It was he who managed to detect the magnetic field, the inner ocean and provide many spectral images. And in 2007 we received not only spectra, but also topographic map of this satellite, taken by the New Horizons probe.

At the moment, there are still a lot of unresolved questions regarding the moons of Jupiter, their suitability for colonization and the potential for life. However, neither NASA, nor Roskosmos, nor the European Union have money for new expeditions yet.

However, things may change in the near future.

The words about the colonization of Ganymede are not just words. The fact is that this satellite, with all the shortcomings (remoteness, radiation, etc.), has many advantages as an “intermediate base” on the way to “deep space”. Water supplies, some magnetic shield, gravity that allows you to spend less energy on takeoff - all this makes Ganymede not the worst candidate, in any case, this satellite of Jupiter offers better starting conditions than the same or ours.

Satellite name: Ganymede;

Diameter: 5270 km;

Pov area: 87,000,000 km²;

Volume: 7.6×10 10 km³;
Weight: 14.82×1022 kg;
Density be: 1936 kg/m³;
Rotation period: 7.15 days;
Period of circulation: 7.15 days;
Distance from Jupiter: 1,070,400 km;
Orbital speed: 1.73 km/s;
equator length: 16,550 km;
Orbital inclination: 0.32°;
Accel. free fall: 1.43 m/s²;
Satellite : Jupiter

Ganymede- the seventh satellite, the third of the Galilean group, as well as the largest satellite in. In size and volume, it even exceeds, but is inferior to it in mass by more than 2 times. Orbit of Ganymede is located at a distance of 1,070,400 kilometers from Jupiter. It takes him seven days and three hours to complete full turn around the planet. Like most known satellites, Ganymede's rotation is synchronized with the period of revolution around, and it always turns the same side to the planet. The internal structure of the satellite is central core with a radius of 500 km, silicate rocks, a mantle and a 900 km layer of ice. Nucleus consists of molten iron and has a density of approximately 5500 kg/m³. In the liquid core of Ganymede, active chemical movements and this generates its own a magnetic field, whose boundary ends at 5300 km from the satellite.

Ganymede is composed of approximately equal amounts of silicate rocks and water ice. It is a fully differentiated body with a liquid core rich in iron. There is an assumption that under a thick layer of ice, as well as at, there may be underground ocean from liquid water. The surface of Ganymede itself is represented by two types of surface landscapes. The dark regions, which occupy a third of the satellite's surface, are covered with gift craters up to four billion years old. The light areas covering the rest of the territory are rich in extensive depressions and ridges, which are somewhat younger. The reason for the disrupted geology of the light regions is not fully understood, but is likely the result of tectonic activity caused by periodic heating. The surface of the third Galilean moon is 40-50% covered with very ancient and thick layer of ice. This is not ordinary ice in the usual sense, due to low temperatures and high internal pressure, such water ice can exist in several modifications with various types crystal lattice.

Like everyone else celestial bodies with a thin atmosphere Climate on Ganymede almost indistinguishable from . Minimum temperature is -200 °C, and in the daytime, sunbeams the satellite can warm up to -120 °C. gas envelope around the satellite consists entirely of oxygen, and has a pressure of 1-2 μPa (10 11 times less atmospheric pressure ).

Expanded color image of Ganymede taken by the Galileo spacecraft in 2001.
Ganymede is the largest moon in the solar system and the only one
moons of Jupiter, named after a male god

Ganymede compared to the Earth and the Moon. Jupiter's moon by volume
3.45 times larger than the Moon and 14.25 times smaller than the Earth

Callisto

Satellite name: Callisto;

Diameter: 4820 km;

Pov area: 73,000,000 km²;

Volume: 5.9×10 10 km³;

Weight: 10.75×1022 kg;

Density be: 1834 kg/m³;

Rotation period: 16.7 days;

Period of circulation: 16.7 days;

Distance from Jupiter: 1,882,000 km;

Orbital speed: 8.2 km/s;

equator length: 15,135 km;

Orbital inclination: 0.19°;

Accel. free fall: 1.24 m/s²;

Satellite : Jupiter

The last Galilean satellite was named after the daughter of King Lycaon and the mistress of Zeus - Callisto. Calisto revolves in a circular orbit at a distance of 1,882,000 km from . Just like the rest of the satellites, its rotation around the planet is synchronous with its own rotation around the axis, so the satellite is always turned on one side to the Giant. The orbital rotation speed is 29,520 km / s, and the duration of the year is twice that of Ganymede - 16 days 16 hours and 48 minutes. Surface layer Callisto is strewn with a network of craters and is covered with a cold and hard icy lithosphere, the thickness of which is different estimates ranges from 80 to 150 km. May be present under the ice salty ocean depth of 50–200 km. At the center of the satellite dense core, consisting of pressed ice and rocks. In 2003 the device "Galileo" made eight close flybys from Callisto, maximum approach - 138 km. It was then, from the resulting images, that scientists were able to describe in detail the surface and atmosphere of the satellite. The ancient surface of Callisto is one of the most heavily cratered in. Craters so many that they simply overlap each other, forming spots with diameters from 5 to 1000 km. Also, no large deviations in the relief were noticed in the pictures. Although the surface of Callisto is not similar in smoothness to the surface, nevertheless, it was not noticed on it. large mountains or volcanoes, and the entire cover of the satellite is a flat relief.

A huge meteorite that fell on the surface of Callisto led to the formation of a giant structure surrounded by ring waves - the so-called Valhalla. In its center is a crater with a diameter of 350 km, and within a radius of 2000 km from it there are small mountain ranges.
Most likely, the satellite was formed from the dust and gas nebula surrounding Jupiter after its formation. Those particles that Jupiter did not have time to absorb,

that such waves were formed from striking force meteorite that fell on the surface of the satellite.

The diameter of Valhalla is 3800 km, and in the center of it there is an impact crater with a diameter of 350 km.

Jupiter's moon Ganymede was discovered by Galileo Galilei on January 7, 1610 using his first ever telescope. On this day, Galileo saw 3 “stars” near Jupiter: Ganymede, Callisto and a “star”, which later turned out to be two satellites - Europa and Io (only the next night the angular distance between them increased enough for separate observation). On January 15, Galileo came to the conclusion that all these objects are actually celestial bodies moving in orbit around Jupiter. Galileo called the four satellites he discovered "Medici planets" and assigned them serial numbers.
The French astronomer Nicolas-Claude Fabry de Peyresque proposed that the satellites be given separate names after four members of the Medici family, but his proposal was not accepted. The discovery of the satellite was also claimed by the German astronomer Simon Marius, who observed Ganymede in 1609, but did not publish data on this in time. Marius tried to give the moons the names "Saturn of Jupiter", "Jupiter of Jupiter" (it was Ganymede), "Venus of Jupiter" and "Mercury of Jupiter", which also did not catch on. In 1614, following Johannes Kepler, he proposed new names for them after the names of those close to Zeus.
However, the name "Ganymede", like the names proposed by Marius for other Galilean satellites, was practically not used until the middle of the 20th century, when it became common. In much of the earlier astronomical literature, Ganymede is designated (in the system introduced by Galileo) as Jupiter III or "Jupiter's third moon". After the discovery of the satellites of Saturn, a designation system based on the proposals of Kepler and Marius began to be used for the satellites of Jupiter.
Ganymede is currently known to be the largest moon in the Jupiter system, as well as the largest moon in the solar system. Its diameter is 5262 km, which exceeds the size of the planet Mercury by 8%. Its mass is 1.482 * 10 23 kg - more than three times the mass of Europe and twice the mass of the Moon, but this is only 45% of the mass of Mercury. Average density Ganymede is less than that of Io and Europa - 1.94 g / cm 3 (only twice as much as that of water), which indicates an increased ice content in this celestial body. Water ice is estimated to be at least 50% total weight satellite.

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CHARACTERISTICS OF GANYMEDE
Other names	Jupiter III
Opening
Discoverer	Galileo Galilei
opening date	January 7, 1610
Orbital characteristics
Periyovium	1,069,200 km
Apoyovy	1,071,600 km
Average orbit radius	1,070,400 km
Orbital eccentricity	0,0013
sidereal period	7.15455296 d
Orbital speed	10.880 km/s
Mood	0.20° (to Jupiter's equator)
physical characteristics
Medium radius	2,634.1 +/- 0.3 km (0.413 Earth)
Surface area	87.0 million km 2 (0.171 Earth)
Volume	7.6 * 10 10 km 3 (0.0704 Earth)
Weight	1.4819 * 10 23 kg (0.025 earth)
Average density	1.936 g/cm3
Acceleration of free fall at the equator	1.428 m/s 2 (0.146 g)
Second space velocity	2.741 km/s
Rotation period	synchronized (turned to Jupiter on one side)
Axis Tilt	0-0.33°
Albedo	0,43 +/- 0,02
Visible magnitude	4.61 (in opposition) / 4.38 (in 1951)
Temperature
superficial	min. 70K / avg. 110K / max. 152K
Atmosphere
Atmosphere pressure	trace
Compound:	oxygen
CHARACTERISTICS OF GANYMEDE

Ganymede is located at a distance of 1,070,400 kilometers from Jupiter, making it the third farthest Galilean satellite. It takes seven days and three hours (7.155 Earth days) to complete one orbit around Jupiter. Like most known moons, Ganymede's rotation is synchronized with that of Jupiter, and it always faces the same side towards the planet. Its orbit has a slight inclination to Jupiter's equator and an eccentricity that varies quasi-periodically due to secular disturbances from the Sun and planets. The eccentricity varies in the range of 0.0009-0.0022, and the inclination - in the range of 0.05°-0.32°. These orbital oscillations cause the tilt of the rotation axis (the angle between this axis and the perpendicular to the plane of the orbit) to change from 0 to 0.33°.
As a result of such an orbit, much less thermal energy is released in the bowels of a celestial body than in Io and Europa, which are closer to Jupiter, which leads to extremely insignificant activity in the ice crust of Ganymede. While flying around the orbit, Ganymede also participates in a 1:2:4 orbital resonance with Europa and Io.

Orbital resonance occurs when forces prevent an object from locking into a stable orbit. Europa and Io regularly resonate each other's orbits to this day, and something similar seems to have happened to Ganymede in the past. At present, Europa takes twice as long to orbit Jupiter, while Ganymede takes four times as long.
The maximum convergence of Io and Europa occurs when Io is at the pericenter, and Europa at the apocenter. Europe is approaching Ganymede, being in its periapsis. Thus, lining up all three of these satellites in one line is impossible. This resonance is called the Laplace resonance.
The modern Laplace resonance is unable to increase the eccentricity of Ganymede's orbit. The current value of the eccentricity is about 0.0013, which may be due to its increase due to resonance in past epochs. But if it is not currently increasing, then the question arises why it has not reset to zero due to tidal energy dissipation in the depths of Ganymede. Perhaps the last increase in eccentricity occurred recently - several hundred million years ago. Since the eccentricity of Ganymede's orbit is relatively low, tidal heating of this satellite is now negligible. However, in the past, Ganymede may have gone through a Laplace-like resonance one or more times, which was able to increase the orbital eccentricity to values ​​of 0.01-0.02. This likely caused significant tidal heating of Ganymede's interior, which could have caused tectonic activity to form an uneven landscape.
There are two hypotheses for the origin of the Laplace resonance of Io, Europa and Ganymede: that it has existed since the appearance of the solar system, or that it appeared later. In the second case, the following development of events is likely: Io raised tides on Jupiter, which led to her moving away from him until she entered into a 2: 1 resonance with Europa; after that, the radius of Io's orbit continued to increase, but part angular momentum was transferred to Europe and she also moved away from Jupiter; the process continued until Europe entered into a 2:1 resonance with Ganymede. Ultimately, the radii of the orbits of these three satellites reached values ​​corresponding to the Laplace resonance.

The modern model of Ganymede suggests that a silicate-ice mantle extends under the ice crust up to a small metal core with a size of about 0.2 Ganymede radius. According to the Galileo spacecraft, in the bowels of Ganymede, between the layers of ice, there may be a huge ocean of liquid water. The conclusion about the existence of an iron core was made on the basis of the discovery of the magnetosphere of Ganymede by the Galileo equipment in 1996-1997. It turned out that the satellite's own dipole magnetic field has a strength of about 750 nT, which exceeds the magnetic field strength of Mercury. Thus, after the Earth and Mercury, Ganymede is the third solid body in the solar system that has its own magnetic field. Ganymede's small magnetosphere is contained within Jupiter's much larger magnetosphere and only slightly deforms its field lines.
Two types of landscape are observed on the surface of Ganymede. A third of the moon's surface is occupied by dark regions dotted with impact craters. Their age reaches four billion years. The rest of the area is occupied by younger light areas covered with furrows and ridges. The reasons for the complex geology of the light regions are not fully understood. It is probably associated with tectonic activity caused by tidal heating.
On a surface Brown color located a large number of bright impact craters surrounded by haloes of light rays of material ejected during impacts. Two large dark regions on the surface of Ganymede are named Galileo and Simon Marius (in honor of the researchers who independently and almost simultaneously discovered the Galilean satellites of Jupiter). The age of the surface of celestial bodies is determined by the number of impact craters that were intensively formed in the solar system 2...3 billion years ago. Absolute scale age is built on the Moon, where the dating was directly (according to the results of radioisotope study of samples of soil delivered to Earth from lava areas). Judging by the number meteorite craters, the most ancient parts of the surface of Ganymede have an age of 3...4 billion years.
On the lighter ice surface of Ganymede, rows of numerous subparallel furrows and ridges are observed, somewhat reminiscent of the surface of Europa. The depth of the light furrows is several hundred meters, the width is tens of kilometers, and the length reaches thousands of kilometers. Furrows are observed on some relatively young local areas of the surface. Apparently, the furrows were formed as a result of stretching of the crust. The features of some parts of the surface resemble traces of the rotation of its large blocks, similar to tectonic processes on Earth.

Terrestrial geographical names are used to designate formations on Ganymede, as well as the names of characters from the ancient Greek myth of Ganymede and characters from the myths of the Ancient East.
An analysis of the features of the ancient surface of Ganymede that has survived to this day allows us to assume that at the initial stage of its existence, young Jupiter radiated much more energy into the surrounding space than now. Jupiter's radiation could lead to partial melting surface ice on satellites close to it, including Ganymede. The morphology of some sections of the satellite's crust can be interpreted as traces of melting. Such dark areas (peculiar seas) are apparently formed by the products of water eruptions.
The satellite has a thin atmosphere, which includes such allotropic modifications oxygen, such as O (atomic oxygen), O 2 (oxygen) and possibly O 3 (ozone). The amount of atomic hydrogen (H) in the atmosphere is negligible. Whether Ganymede has an ionosphere is unclear.
First spacecraft, who studied Ganymede, became Pioneer 10 in 1973. Much more detailed studies were carried out by the Voyager spacecraft in 1979. The Galileo spacecraft, which has been studying the Jupiter system since 1995, has discovered an underground ocean and Ganymede's magnetic field.

Evolution of Ganymede

Ganymede probably formed from an accretion disk or gas and dust nebula that surrounded Jupiter some time after its formation. The formation of Ganymede probably took approximately 10,000 years (an order of magnitude less than the estimate for Callisto). Jupiter's nebula likely had relatively little gas when the Galilean moons formed, which may explain the very slow formation of Callisto. Ganymede formed closer to Jupiter, where the nebula was denser, which explains its faster formation. It, in turn, led to the fact that the heat released during accretion did not have time to dissipate. This may have caused the ice to melt and rock to separate from it. The stones settled in the center of the satellite, forming the core. Unlike Ganymede, during the formation of Callisto, heat had time to be removed away, the ice in its depths did not melt and differentiation did not occur. This hypothesis explains why the two moons of Jupiter are so different, despite the similarity in mass and composition. Alternative theories attribute the higher internal temperature of Ganymede to tidal heating or more intense exposure to later heavy bombardment.
The core of Ganymede after formation retained most heat accumulated during accretion and differentiation. It slowly releases this heat to the icy mantle, working as a kind of heat battery. The mantle, in turn, transfers this heat to the surface by convection. The decay of radioactive elements in the core continued to heat it up, causing further differentiation: an inner core of iron and iron sulfide and a silicate mantle were formed. Thus Ganymede became a fully differentiated body. In comparison, the radioactive heating of the undifferentiated Callisto only caused convection in its icy interior, which effectively cooled them and prevented large-scale ice melt and rapid differentiation. The process of convection on Callisto caused only a partial separation of the rocks from the ice. Currently, Ganymede continues to slowly cool. The heat coming from the core and silicate mantle allows the underground ocean to exist, and the slow cooling of the liquid core of Fe and FeS causes convection and maintains the generation of a magnetic field. The current heat flux from the bowels of Ganymede is probably higher than that of Callisto.

physical characteristics

The average density of Ganymede is 1.936 g/cm3. Presumably it consists of equal parts rocks and water (mostly frozen). The mass fraction of ice lies in the range of 46-50%, which is slightly lower than that of Callisto. Some volatile gases, such as ammonia, may be present in ice. The exact composition of the rocks of Ganymede is not known, but it is probably close to the composition of ordinary chondrites of groups L and LL, which differ from H-chondrites by a smaller full content iron, a lower content of metallic iron and a greater content of iron oxide. The ratio of the masses of iron and silicon on Ganymede is 1.05-1.27 (for comparison, in the Sun it is 1.8).
The surface albedo of Ganymede is about 43%. Water ice is present on almost the entire surface and its mass fraction fluctuates between 50-90%, which is significantly higher than on Ganymede as a whole. Middle infrared spectroscopy showed the presence of extensive absorption bands of water ice at wavelengths of 1.04, 1.25, 1.5, 2.0 and 3.0 µm. Light areas are less even and have large quantity ice compared to dark ones. Analysis of the ultraviolet and near infrared spectrum with high resolution obtained by the Galileo spacecraft and ground-based instruments showed the presence of other substances: carbon dioxide, sulfur dioxide and, possibly, cyanide, sulfuric acid and various organic compounds. According to the results of the Galileo mission, the presence of a certain amount of tholins on the surface is assumed. The Galileo results also showed the presence of magnesium sulfate (MgSO 4 ) and possibly sodium sulfate (Na 2 SO 4 ) on the surface of Ganymede. These salts could have formed in the underground ocean.
The surface of Ganymede is asymmetric. Leading hemisphere(turned in the direction of the movement of the satellite in orbit) is lighter than the slave. On Europe the situation is the same, but on Callisto it is the opposite. The trailing hemisphere of Ganymede seems to have more sulfur dioxide. Quantity carbon dioxide it is the same on both hemispheres, but it is not near the poles. Impact craters on Ganymede (except one) do not show carbon dioxide enrichment, which also distinguishes this satellite from Callisto. The underground reserves of carbon dioxide on Ganymede were probably depleted in the past.

Internal structure
Presumably, Ganymede consists of three layers: a molten iron or iron sulfide core, a silicate mantle, and an outer layer of ice 900-950 kilometers thick. This model is confirmed by a small moment of inertia, which was measured during the flyby of Ganymede "Galileo" - (0.3105 +/- 0.0028) * mr 2 (the moment of inertia of a homogeneous ball is 0.4 * mr 2). Ganymede has the lowest coefficient in this formula among the solid bodies of the solar system. The existence of a molten iron-rich core provides a natural explanation for Ganymede's own magnetic field, which was discovered by Galileo. Convection in molten iron, which has a high electrical conductivity, is the most reasonable explanation for the origin of the magnetic field.
The exact thickness of the various layers in the bowels of Ganymede depends on the accepted value of the composition of silicates (the proportions of olivine and pyroxenes), as well as on the amount of sulfur in the core. The most probable value of the core radius is 700-900 km, and the thickness of the outer ice mantle is 800-1000 km. The remainder of the radius falls on the silicate mantle. The density of the core is presumably 5.5-6 g/cm 3 , and that of the silicate mantle is 3.4-3.6 g/cm 3 . Some models of Ganymede's magnetic field generation require a solid core of pure iron inside a liquid core of Fe and FeS, which is similar to the structure of the Earth's core. The radius of this core can reach 500 kilometers. The temperature in the core of Ganymede is supposedly 1500-1700 K, and the pressure is up to 10 GPa.

Studies of Ganymede's magnetic field indicate that there may be an ocean of liquid water beneath its surface.

Evidence for an ocean on Ganymede The diagram shows a pair of aurora belts on Jupiter's moon Ganymede. Their displacement / movement gives an idea of ​​the internal structure of Ganymede. Ganymede has a magnetic field created by an iron core. Since the satellite is located close to Jupiter, it is completely included in the magnetic field of the giant planet. Under the influence of Jupiter's magnetic field, the aurora belts on Ganymede are shifting. The fluctuations are less pronounced if there is a liquid ocean under the surface. Numerous observations have confirmed the existence of a large amount of salt water under the ice crust of Ganymede, which affects its magnetic field.

Space Telescope. Hubble, observing the aurora belts on Ganymede in ultraviolet light, confirmed the existence of an ocean on Ganymede. The location of the belts is determined by the magnetic field of Ganymede, and their displacement is due to interaction with Jupiter's huge magnetosphere.

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Numerical modeling of the satellite's interior, performed in 2014 by the staff of the Laboratory jet propulsion NASA has shown that this ocean is probably multi-layered: liquid layers are separated by layers of ice different types(ice I, III, V, VI). The number of liquid interlayers possibly reaches 4; their salinity increases with depth.

Sandwich model of the structure of Ganymede (2014) Previous models of Ganymede's structure showed the ocean sandwiched between the top and bottom layers of ice. New model based on laboratory experiments by simulating salty seas and liquids, shows that Ganymede's oceans and ice can form multiple layers. The ice in these layers is pressure dependent. That. "Ice I" is the least dense form of ice and can be compared to the ice mixture in chilled drinks. As the pressure increases, the ice molecules are closer to each other and, consequently, the density increases. The oceans of Ganymede reach a depth of 800 km, respectively, they experience much more pressure than on Earth. The deepest and densest layer of ice is called "Ice VI". In the presence of enough salts, the liquid can be dense enough to sink to the very bottom and even below the level of "Ice VI". Moreover, the model shows that rather strange phenomena can occur in the uppermost liquid layer. The liquid, cooling from the upper ice layer (crust), descends in the form of cold currents, which form the "Ice III" layer. AT this case when cooled, the salt precipitates and then sinks down, while at the level "Ice III" an ice / snow slush is formed. According to another group of scientists, such a structure of Ganymede cannot be stable, but it could well have preceded the model with one huge ocean.

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Ganymede is the largest moon of Jupiter and the largest moon in the solar system. It was discovered by Galileo Galilei in 1610 and named after Simon Marius, a lover of the god Jupiter. Ganymede was the first discovered satellite after the Moon.

The diameter of Ganymede is 5280 km, which is larger than that of Mercury. It rotates at a distance of just over 1 million km from Jupiter and is the seventh of the planet's 16 satellites. Ganymede is large enough to generate its own magnetic field, which is very unusual for satellites.

Ganymede is always turned to Jupiter by the same side. This is a fairly common phenomenon, called synchronicity. Other a prime example The synchronic relation between the planet and the satellite is the Earth and the Moon. Ganymede rotates in the same direction as Jupiter. It has an almost circular orbit, which means that its eccentricity (a measure of how close a satellite is to an orbit) is quite small. A circular orbit has an eccentricity equal to zero. The tilt angle of Ganymede is less than its level, which means that the satellite rotates directly in the plane of Jupiter's equator.

And although Ganymede is always turned to Jupiter on one side, there are signs that this was not always the case. If the satellite were always turned to the planet with only one side, then this would mean that on its one side there should be more meteorite craters, as in the case of Callisto. However, this is not characteristic of Ganymede. Another fact pointing to changes from the side of the ice shell facing Jupiter is the catena found on the back side of Ganymede. Caten appears due to a number of fragments of a comet that was destroyed by Jupiter's magnetic field, but did not fall on the planet, because it hit its satellite. If Ganymede were always turned on one side to Jupiter, then the catena would form only on the front side of the satellite.

The surface of Ganymede is covered in ice mixed with carbon-rich soil, which reflects a large amount of sunlight. When the ice below the moon's surface heats up and melts, it breaks through to the surface. Soil that is denser than water is submerged. After the water freezes, which leads to the formation of a bright spot on the surface. The water heats up either due to radioactive decay or under the influence of the tides. Ganymede is affected not only by the gravity of Jupiter and Callisto: the satellite also has a Laplace resonance, which arises from the forces of the moons of Io and Europa. Every time Ganymede revolves around Jupiter, Europa, a satellite inside Ganymede, goes around the planet twice, and Io, located inside Europa, manages to go around Jupiter 4 times. Thus, during each rotation, the three satellites align, which increases the gravitational effect. This increases the gravitational attraction, and after its decrease, the orbits not only become elliptical, but acquire more voltage within the satellites themselves. These tides generate heat that melts the ice on Ganymede, making it smoother than any other planet/moon.

Ganymede is covered with ice by 45-55%. The satellite's density is determined by ice and carbonaceous silicates, indicating a mixture of the two materials.

Ganymede has its own magnetic field, which is opposite to Jupiter's magnetic field.. It also displays an induced magnetic field caused by strong rotation under Jupiter's angular field. The induced field speaks of a conducting ocean deep below the ice surface. If there are enough dissolved minerals in the ocean for a powerful conductor, then it can generate its own magnetic field. Due to Jupiter's strong magnetic field, Ganymede has many charged particles. This is believed to cause the formation of molecular oxygen O2 and ozone O3, which have been found on the surface of Ganymede.

Since the orbit of Ganymede is in the same plane as Jupiter, this suggests that both the planet and the satellite were formed as a result of the same process. Jupiter formed in a very hot and dense region. Ganymede formed in a colder region where water does not boil, but freezes and becomes part of the moon.

Ganymede is the largest moon of Jupiter and all solar system, which is the size of a planet. Its diameter is 5268 km. It got its name from the son of the Trojan king and the nymph Kalliroi. The gods have taken handsome boy to heaven, where he became the favorite and butler of Zeus.

Its average density is low - 1.94 g/cm 3 . In general, the density of Galilean satellites decreases with distance from Jupiter. The density of Io is 3.55, Europa - 3.01, and Callisto - 1.83 g/cm 3 , which indicates an increase in the proportion of ice in their composition as they move away from Jupiter. The water ice of Ganymede makes up to 50% of its mass. Ganymede has the most correct form, its differences from the shape of the ball were not found. Some characteristics of the Ganymede satellite are shown in the table

Surface

The surface of Ganymede is dotted with impact craters, some of them reaching 100% albedo. The age of the surface of Ganymede turned out to be very large, some of the most ancient dark areas - up to 3-4 billion years. Lighter areas are often intersected by valleys and ridges for many thousands of kilometers. The width of these formations is up to tens of kilometers, the depth is only a few hundred meters. These areas are younger, and scientists suggest that they arose under the action of stretching of the ice crust as a result of local tectonics.

Large-scale images of the surface, obtained by the Galileo spacecraft, turned the previous ideas about the geological past of this satellite upside down. They show ancient icefields pitted with craters and young plains cut with ridge-shaped mountains, pitted with craters and tectonically deformed. In general, about half of the area covered by meteorite and comet craters has been re-altered by traces of volcanic and tectonic activity. An image of the surface of Ganymede taken by the Galileo spacecraft

More recent images have shown the possible presence of liquid water on Ganymede.

Magnetic field and magnetosphere of Ganymede

During the rendezvous of the spacecraft Galileo with Ganymede, a large increase in the strength of the magnetic field was detected, i.e. for the first time at the satellite of the planet is clearly fixed own magnetosphere. Two instruments on Galileo - a plasma spectrometer, which records the number and composition of charged particles, and a magnetometer, which records the direction and magnitude of the magnetic field - dramatically changed their readings when approaching Ganymede. The concentration of ions and electrons increased by more than 100 times, and the magnitude of the magnetic field increased by almost 5 times, its direction changed, pointing directly to Ganymede. This magnetic cocoon protects the satellite from the magnetic influence of the main giant body - Jupiter.
Combining open magnetic field data with known gravitational data, scientists concluded that Ganymede has metal core, surrounded by a rocky silicate mantle, which in turn is covered with an icy crust. Such differentiated structure, perhaps, and causes a magnetic field, which in turn creates a magnetosphere. Formerly the only known solid bodies solar system, having a magnetic field, were the planets Mercury and Earth. Magnetic fields have now been found for all of Jupiter's Galilean satellites - Io, Europa, Ganymede and Callisto.
On Ganymede own magnetic field strong enough to form a magnetosphere with a sharply defined boundary within Jupiter's magnetosphere. Recent observations from Galileo have shown the presence of a magnetic field around Callisto as well. The magnetometer installed on Galileo showed the presence of a magnetic field in Europe, and the northern magnetic pole pointing in a strange direction. The magnitude of the magnetic field is about one quarter of the strength of Ganymede's magnetic field.

Orbit, theory of motion, ephemeris

Ganymede makes one revolution around the planet in 7.154553 days. Ganymede is moving on resonant orbit, i.e. makes one revolution in two revolutions of another Galilean satellite - Europa, which in turn also makes one revolution in two revolutions of Io. Thus, the orbital periods of the satellites of Europa and Ganymede are in a 1:2 resonance, Io and Ganymede are in a 1:4 resonance, i.e. in the system of Galilean satellites there is a triple resonance 1: 2: 4. The main elements of the orbit are given in the table

Currently the best theory motion of the Galilean moons of Jupiter is Liske's theory. Most complete picture the motion of the Galilean satellites was presented by Ferras-Mello in the monograph "Dynamics of the Galilean satellites of Jupiter". More about the dynamics of Galilean satellites... Calculation of ephemeris for satellite observations at any time can be done on the website of the Bureau of Longitudes (Paris).

Rotation

Ganymede is in synchronous rotation with Jupiter, i.e. the period of its rotation around the axis is equal to the period of revolution of the satellite around Jupiter.
Recommended values ​​for the direction to the north pole of rotation and the first meridian of the satellites of Jupiter (1994, IAUWG).
Right ascension and declination are standard equatorial coordinates at the J2000 equator for the J2000 epoch.
Coordinates north pole unchanged plane
= 66°.99.
T - interval in Julian centuries (36525 days each) from the standard epoch,
d - interval in days from standard epoch,
The standard epoch is January 1.5, 2000, i.e. 2451545.0 TDB

where
J4 = 355.°80 + 1191.°3 T
J5 = 119.°90 + 262.°1 T
J6 = 229.°80 + 64.°3 T