Satellite Ganymede: history of discovery, physical characteristics. Satellite of the planet Jupiter

But in all solar system. In size (5268 km), it is 8% larger than Mercury, although it is inferior to it in mass. The mass of Ganymede is 1.48 * 10 23 kg, which is 2 times the mass of the moon. It revolves around Jupiter in a regular circular orbit at a distance of 1.07 million km and makes one revolution in 7.155 Earth days. From this distance, Jupiter looks 15.2 times the size of the Moon in Earth's sky.
Like the rotation of all the other Galilean moons of Jupiter, Ganymede's rotation is tidally synchronized with its orbital motion, so that it faces Jupiter on only one side.

The ancient surface of Ganymede is littered with numerous impact craters. Young deep craters expose the pure ice of the depths and look bright white (their albedo is close to 100%). However, the surface of the satellite also bears obvious traces of active tectonic processes. Approximately half of the surface of its antiquity, dark color and an abundance of craters resemble the surface of Callisto, its age is estimated at 3 billion years. The brighter regions are much younger, their age is estimated at 0.5–1 billion years. The ice surface of the light areas is crossed by numerous ridges and faults.

The surface of Ganymede experiences sharp temperature contrasts. In equatorial latitudes, the temperature rises to 160K (-113C) in the afternoon, drops to 120K at sunset, and quickly drops after sunset to 85-90K. At the poles, where the sun is low on the horizon, even daytime temperatures do not rise above 120K. Both day and night on Ganymede last 3.6 Earth days.

The moon's icy surface is continuously bombarded by high-energy charged particles from Jupiter's magnetosphere and illuminated by ultraviolet light from the Sun. The knocking out of water vapor molecules and their photodissociation under the influence of solar ultraviolet lead to the appearance of Ganymede's ephemeral atmosphere, consisting mainly of oxygen molecules. Its integral density is only 10 14 - 10 15 molecules per square centimeter. For comparison, one cubic centimeter of air under normal conditions (0С, 1 atm.) contains 2.68 * 10 19 molecules (so that the atmosphere of Ganymede has a density comparable to that of terrestrial air, it will all have to be compressed into a layer ~ 0.4 microns thick ). The temperature of the atmosphere is close to 150K.

Another surprise presented by AMS Galileo was the discovery of a magnetic field near Ganymede and its own magnetosphere, completely immersed in Jupiter's magnetosphere. The magnitude of the field is small, it is only 750 nT at the equator of the satellite, but this is almost 6 times greater than the magnetic field strength of Jupiter in the orbit of Ganymede (107-118 nT). The axis of the magnetic dipole is inclined by 10 degrees to the axis of rotation of the satellite. The magnetosphere of Ganymede extends approximately 2 Ganymede radii around this satellite (thus, a cavity with a diameter of ~4 Ganymede radii is formed in Jupiter's magnetosphere).
There are currently two hypotheses regarding the origin of Ganymede's magnetic field. According to one of them, the magnetic field is induced by a dynamo mechanism during the rotation of the molten iron (or mixed with iron sulfide) core of Ganymede (the same mechanism is responsible for the emergence of the Earth's magnetic field). This assumption is supported by the "correct" dipole character of the satellite's magnetic field. According to the second hypothesis, Ganymede's magnetic field is induced in a salty ocean located under a thick (130-150 km) ice crust. It is possible that both of these mechanisms are at work.

The internal structure of Ganymede.
Unlike Callisto, Ganymede has undergone gravitational differentiation and consists of several layers.

At the center of this satellite is a molten core composed of a mixture of iron and iron sulfide. The mantle extends above rocks, even higher - an extensive mantle of partially molten ice. The last 130-150 km is made up of solid ice crust.

Ganymede in numbers:
Semi-major axis of the orbit around Jupiter: 1,070,000 km.
Orbital eccentricity: 0.002
Orbital inclination to Jupiter's equator: 0.195 degrees
Orbital period: 7.155 Earth days
Equatorial radius: 2634 km (1.516 lunar radius).
Mass: 1.48 * 1023 kg (2.014 moon masses)
Average density: 1.94 g/cc
Acceleration of free fall on the surface: 1.42 m/s 2 (approximately 6.9 times less than on Earth)
Second escape velocity: 2.74 km/s
Albedo: 0.42
Surface temperature: 85-160K

Map of Ganymede (careful, 4.5 Mb!)

Sources:
"Discovery of Ganymede`s magnetic field by the Galileo spacecraft", Nature, vol. 384, December 12, 1996
Cratering Rates on the Galilean Satellites

Ganymede in NASA Photojournal
Ganymede in the NATSAT Information Guide

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. The average density of Ganymede is less than that of Io and Europa - 1.94 g / cm 3 (only twice 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
Apparent magnitude	4.61 (in opposition) / 4.38 (in 1951)
Temperature
superficial	min. 70K / avg. 110K / max. 152K
Atmosphere
Atmosphere pressure	trace
Composition:	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, significantly 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 of the angular momentum was transferred to Europa and it 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 the surface Brown color there is a large number of bright impact craters surrounded by halos 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. The absolute age scale is based on the Moon, where dating was performed directly (according to the results of a radioisotope study of samples of soil brought to Earth from lava areas). Judging by the number of meteorite craters, the most ancient parts of the surface of Ganymede are 3-4 billion years old.
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 symbols are used to designate formations on Ganymede. geographical names, 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 of 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 of oxygen 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.
The first spacecraft to study Ganymede was 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 separate from it. rocks. 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 Ganymede's higher internal temperature 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 the L and LL groups, which differ from H-chondrites in their lower total iron content, lower metallic iron content, and more 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. Near infrared spectroscopy showed the presence of extensive water ice absorption bands 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 high-resolution ultraviolet and near-infrared spectra taken 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. The leading hemisphere (turned in the direction of the satellite's orbit) is lighter than the driven one. 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. The amount of carbon dioxide is the same in 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. underground reserves 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 under the ice crust of Ganymede a large number salt water, 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 NASA's Jet Propulsion Laboratory, showed that this ocean is probably multi-layered: liquid layers are separated by layers of ice of 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. A new model based on laboratory experiments 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. In this case, when cooled, the salt precipitates and then sinks down, while at the level "Ice III" an ice/snow slurry 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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An image of the anti-Jovian hemisphere of Ganymede taken by the Galileo spacecraft. Light surfaces, traces of recent impacts, a ridged surface, and a white north polar cap (upper right of image) are rich in water ice

Ganymede (ancient Greek Γανυμήδης) is one of the Galilean satellites, the seventh in distance from it among all of it and the largest satellite in. Its diameter is 5268 kilometers, which is 2% larger than that of (the second largest satellite in the solar system) and 8% larger than that of . At the same time, the mass of Ganymede is only 45% of the mass of Mercury, but among the satellites it is a record. Ganymede exceeds the mass by 2.02 times. Flying around the orbit in about seven days, Ganymede participates in a 1: 2: 4 orbital resonance with two other satellites of Jupiter - and.

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. Presumably in its bowels at a depth of about 200 km between the layers of ice there is an ocean of liquid water. 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.

Ganymede is the only moon in the solar system that has its own magnetosphere. Most likely, it is created by convection in a liquid core rich in iron. Ganymede's small magnetosphere is contained within Jupiter's much larger magnetosphere and only slightly deforms its field lines. The satellite has a thin atmosphere, which includes such allotropic modifications of oxygen as O (atomic oxygen), O2 (oxygen), and possibly O3 (ozone). The amount of atomic hydrogen (H) in the atmosphere is negligible. Whether Ganymede has an ionosphere is unclear.

Ganymede was discovered by Galileo Galilei, who saw it on January 7, 1610. Soon Simon Marius proposed to name it in honor of the butler Ganymede. The first to study Ganymede was Pioneer 10 in 1973. Much more detailed studies were carried out by the Voyager spacecraft in 1979. The spacecraft, which has been studying the Jupiter system since 1995, has discovered an underground ocean and Ganymede's magnetic field. In 2012, the European Space Agency approved a new mission to explore Jupiter's icy moons, JUICE; its launch is planned for 2022, and arrival in the Jupiter system - for 2030. The Europa Jupiter System Mission is scheduled for 2020, integral part which, perhaps, will be the Russian "Laplace".

History of discovery and naming

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, 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 by the names of Zeus's associates (including Ganymede):

... Then there was Ganymede, the beautiful son of the Trojan king Tros, whom Jupiter, taking the form of an eagle, kidnapped to heaven holding on his back, as the poets fabulously describe ... Thirdly, because of the majesty of the light, Ganymede ...

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 satellites, a designation system based on proposals by Kepler and Marius began to be used for the satellites of Jupiter. Ganymede is the only Galilean moon of Jupiter named after a male figure - according to a number of authors, he (like Io, Europa and Callisto) was the beloved of Zeus.

According to Chinese astronomical records, in 365 BC. e. Gan Te discovered the satellite of Jupiter with the naked eye (probably it was Ganymede).

Origin and evolution

Comparison of the sizes of the Moon, Ganymede and the Earth

Ganymede probably formed from or 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 Ganymede's higher internal temperature to tidal heating or more intense exposure to later heavy bombardment.

The core of Ganymede, after formation, retained most of the 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.

Orbit and rotation

Ganymede is located at a distance of 1,070,400 kilometers from Jupiter, making it the third farthest Galilean satellite. It takes him seven days and three hours to make a complete revolution 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 small inclination to Jupiter's equator and eccentricity, which change quasi-periodically due to secular perturbations from 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°.

Laplace resonance (orbital resonance) of the satellites Ganymede, Europa and Io

Ganymede is in orbital resonance with Europa and Io: for every revolution of Ganymede around the planet, there are two revolutions of Europa and four revolutions of Io. 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 orbital eccentricity of Ganymede is relatively low (0.0015 on average), the 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 of the angular momentum was transferred to Europa and it 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.

physical characteristics

Composition

A sharp border between the ancient dark landscape of the Nicholson area and the young bright rut of Arpagia

The average density of Ganymede is 1.936 g/cm3. Presumably, it consists of equal parts of rock 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 the L and LL groups, which differ from H-chondrites in their lower total iron content, lower metallic iron content, and more 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%. There is water ice on almost the entire surface and its mass fraction ranges from 50-90%, which is much higher than on Ganymede as a whole. Near infrared spectroscopy showed 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 more ice than dark areas. Analysis of high-resolution ultraviolet and near-infrared spectra taken 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 (MgSO4) and possibly sodium sulfate (Na2SO4) on the surface of Ganymede. These salts could have formed in the underground ocean.

The surface of Ganymede is asymmetric. The leading hemisphere (turned in the direction of the satellite's orbit) is lighter than the driven one. 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. The amount of carbon dioxide is the same in 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

Possible internal structure of Ganymede

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)×mr2 (the moment of inertia of a homogeneous ball is 0.4×mr2). 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/cm3, and that of the silicate mantle is 3.4-3.6 g/cm3. 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. Numerical modeling of the satellite's interior, performed in 2014 by NASA's Jet Propulsion Laboratory, showed that this ocean is probably multi-layered: liquid layers are separated by layers of ice of different types (ice I, III, V, VI). The number of liquid interlayers possibly reaches 4; their salinity increases with depth.

Surface

Mosaic from photographs of the anti-Jovian hemisphere of Ganymede. The dark ancient zone in the upper right corner is the region of Galilee. It is separated from the area of ​​Marius (the smaller dark area to the left) by the light potholes of Uruk. The bright radiant structure below is fresh ice ejected from the relatively young Osiris crater.

The surface of Ganymede is a mixture of two types of patches: very ancient, heavily cratered dark areas and somewhat younger (but still ancient) light areas covered with furrows, grooves and ridges. The dark areas of the surface occupy approximately 1/3 of the entire area and contain clays and organic matter, which may reflect the composition from which the satellites of Jupiter were formed.

It is not yet known what caused the heating required to form the grooved surface of Ganymede. According to modern concepts, such a surface is a consequence of tectonic processes. Cryovolcanism is thought to play a minor role, if at all. The forces that created strong stresses in the lithosphere of Ganymede, necessary for tectonic movements, could be associated with tidal heating in the past, which may have been caused by unstable orbital resonances through which the satellite passed. The tidal deformation of the ice could heat up the bowels of Ganymede and cause stress in the lithosphere, which led to the appearance of cracks, horsts and grabens. At the same time, the old dark surface was erased on 70% of the satellite area. The formation of the striated surface can also be associated with the early formation of the core of the satellite and subsequent tidal heating of its interior, which, in turn, caused an increase in Ganymede by 1-6% due to thermal expansion and phase transitions in ice. Possibly, in the course of subsequent evolution, plumes from heated water rose from the core to the surface, causing deformations of the lithosphere. The most probable modern source of heat in the interior of the satellite is radioactive heating, which can (at least partially) ensure the existence of a subsurface water ocean. Modeling shows that if the eccentricity of Ganymede's orbit were an order of magnitude higher than the current one (and this may have been in the past), tidal heating could be stronger than radioactive.

Photo of Ganymede (in the center meridian 45°W). Dark areas - Perrine area (top) and Nicholson area (bottom); radiant craters - Tros (upper right) and Chisti (lower left)

There are impact craters on the surface of both types, but in dark areas they are especially numerous: these areas are saturated with craters and, apparently, their relief was formed mainly by collisions. There are much fewer craters in the bright furrowed areas, and they did not play a significant role in the evolution of their topography. The density of cratering of the dark areas indicates an age of 4 billion years (similar to the continental regions of the Moon).

Gula and Aheloy craters (below). Everyone has a “shaft” and a “pedestal” from emissions

The light areas are younger, but by how much is unclear. The cratering of the surface of Ganymede (as well as the Moon) reached a special intensity about 3.5-4 billion years ago. If these data are accurate, then most of the impact craters are from that era, and after that they added little in number. Some craters are crossed by furrows, and some formed on top of the furrows. This suggests that some furrows are quite ancient. In places there are relatively young craters with rays of ejecta radiating from them. The craters of Ganymede are flatter than those on Mercury or the Moon.

This is probably due to the fragility of Ganymede's icy crust, which can (or could) flatten under the influence of gravity. Ancient craters that are almost completely flattened (a kind of "ghost" of craters) are known as palimpsests; one of the largest palimpsests of Ganymede is the Memphis facula with a diameter of 360 km.

Image of the trailing hemisphere of Ganymede taken from the Galileo spacecraft (colors enhanced). In the lower right corner, the bright rays of the Tashmet crater are visible, and in the upper right - large field ejecta from Hershef crater. Part of Nicholson's dark area is at the bottom left. From the top right, it borders on the ruts of Harpagia.

One of the remarkable geostructures of Ganymede is a dark area called the Galilee region, where a network of multidirectional furrows is visible. Probably, this region owes its appearance to the period of rapid geological activity of the satellite.

Ganymede has polar ice caps believed to be made of water frost. They cover latitudes above 40°. The polar caps were first observed during the Voyager flyby. They are probably formed by water molecules knocked out of the surface when bombarded with plasma particles. Such molecules could migrate to high latitudes from low latitudes due to temperature differences, or they could originate from the polar regions themselves. The results of calculations and observations allow us to judge that the latter is true. The presence of its own magnetosphere in Ganymede leads to the fact that charged particles intensively bombard only weakly protected - polar - regions. The resulting water vapor is deposited mainly in the coldest places of these same areas.

Atmosphere and ionosphere

In 1972, a group of Indian, British and American astronomers working at the Indonesian Bossa Observatory reported the discovery of a thin atmosphere around a satellite while observing its occultation of a star. They estimated the surface pressure of the atmosphere at 0.1 Pa. However, in 1979, Voyager 1 observed Ganymede's occultation of a star (κ Centauri) and obtained contradictory results. These observations were made in the far ultraviolet at wavelengths below 200 nm and were much more sensitive to the presence of gases than the 1972 measurements in visible light. No atmosphere was detected by Voyager's sensors. The upper limit of concentration was at the level of 1.5·10 9 particles/cm 3 that corresponds to a surface pressure of less than 2.5 µPa. And this is almost 5 orders of magnitude less than the 1972 estimate.

The existence of a neutral atmosphere implies the existence of an ionosphere around the satellite, because oxygen molecules are ionized by collisions with fast electrons arriving from the magnetosphere and the solar hard ultraviolet. However, the nature of Ganymede's ionosphere is as controversial as the nature of the atmosphere. Some Galileo measurements have shown an increased density of electrons near the satellite, indicating the presence of an ionosphere, while other attempts to fix it have failed. The electron concentration near the surface, according to various estimates, ranges from 400 to 2500 cm 3 . For 2008, the parameters of the possible ionosphere of Ganymede have not been established.

Temperature map on Ganymede

An additional indication of the existence of an oxygen atmosphere of Ganymede is the detection of gases frozen into ice on its surface from spectral data. The discovery of ozone (O3) absorption bands was reported in 1996. In 1997, spectral analysis revealed absorption lines of dimer (or diatomic) oxygen. Such absorption lines can only appear if oxygen is in a dense phase. The best explanation is that molecular oxygen is frozen into ice. The depth of dimeric absorption bands depends on latitude and longitude (but not on surface albedo) - they tend to decrease with latitude, while the trend for O3 is opposite. Laboratory experiments have shown that at a temperature of 100 K, which is characteristic of the surface of Ganymede, O2 dissolves in ice, and does not collect in bubbles.

Having discovered sodium in the atmosphere of Europa, scientists began to look for it in the atmosphere of Ganymede. In 1997, it became clear that it was not there (more precisely, at least 13 times less than in Europe). This may be due to its lack on the surface, or the fact that Ganymede's magnetosphere prevents charged particles from knocking it out. Among other things, atomic hydrogen has been observed in the atmosphere of Ganymede. It was observed at a distance of up to 3000 km from the satellite surface. Its concentration at the surface is about 1.5·10 4 cm 3 .

Magnetosphere

The Galileo spacecraft from 1995 to 2000 made six close flybys near Ganymede (G1, G2, G7, G8, G28 and G29) and found that Ganymede has a fairly powerful magnetic field and even its own magnetosphere, independent of the magnetic field Jupiter. The magnitude of the magnetic moment is 1.3×10 13 T m 3 , which is three times greater than that of Mercury. The axis of the magnetic dipole is tilted by 176° with respect to the axis of rotation of Ganymede, which means that it is directed against the magnetic moment of Jupiter. The north magnetic pole of Ganymede is below the plane of the orbit. The induction of the dipole magnetic field created by the constant magnetic moment at the equator of the satellite is 719 ± 2 nT (for comparison, the induction of Jupiter's magnetic field at the distance of Ganymede is 120 nT). The opposite direction of the magnetic fields of Ganymede and Jupiter makes magnetic reconnection possible. The induction of Ganymede's own magnetic field at its poles is twice that at the equator, and is equal to 1440 nT.

Ganymede is the only moon in the solar system that has its own magnetosphere. It is very small and immersed in Jupiter's magnetosphere. Its diameter is approximately 2-2.5 of the diameter of Ganymede (which is 5268 km). Ganymede's magnetosphere has a region of closed field lines below 30° latitude where charged particles (electrons and ions) are trapped, creating a kind of radiation belt. The main type of ions in the magnetosphere are oxygen ions O+, which is in good agreement with the rarefied oxygen atmosphere of the satellite. In the caps of the polar regions at latitudes above 30°, the magnetic field lines are not closed and connect Ganymede with Jupiter's ionosphere. In these regions, high-energy electrons and ions (tens and hundreds of kiloelectronvolts) were found, which can cause the auroras observed around the poles of Ganymede. In addition, heavy ions are continuously deposited on the polar surface of the moon, pulverizing and darkening the ice.

The magnetic field of Ganymede in the field of Jupiter. Closed field lines are marked in green

The interaction between Ganymede's magnetosphere and Jovian plasma resembles in many ways the interaction between the solar wind and Earth's magnetosphere. The plasma co-rotates with Jupiter and collides with Ganymede's magnetosphere on its trailing side, as does the solar wind with Earth's magnetosphere. The main difference is the speed of the plasma flow: supersonic in the case of and subsonic in the case of Ganymede. That is why the magnetic field of Ganymede does not have a shock wave from the retarded side.

In addition to the magnetic moment, Ganymede has an induced dipole magnetic field. It is caused by changes in Jupiter's magnetic field near the moon. The induced dipole moment is directed towards or away from Jupiter (according to Lenz's rule). The induced magnetic field of Ganymede is an order of magnitude weaker than its own. Its induction at the magnetic equator is about 60 nT (half the field strength of Jupiter there). The induced magnetic field of Ganymede resembles those of Callisto and Europa and indicates that this satellite also has a subsurface water ocean with high electrical conductivity.

Since Ganymede is completely differentiated and has a metallic core, its permanent magnetic field is probably generated in the same way as the earth's: as a result of the movement of electrically conductive matter in the bowels. If the magnetic field is caused by a magnetohydrodynamic effect, then this is probably the result of the convective movement of various substances in the core.

Despite the presence of an iron core, Ganymede's magnetosphere remains a mystery, especially since other similar bodies do not have it. From some studies it follows that such a small core should already have cooled to the point where the movement of fluid and the maintenance of a magnetic field are impossible. One explanation is that the field is maintained by the same orbital resonances that led to the complex surface topography: due to tidal heating due to orbital resonance, the mantle protected the core from cooling. Another explanation is the residual magnetization of silicate rocks in the mantle, which is possible if the satellite had more strong field in past.

Study of

Image of Ganymede taken by Pioneer 10 in 1973

Jupiter (like all other gas planets) was purposefully studied exclusively by NASA interplanetary stations. Several spacecraft explored Ganymede up close, including four flybys in the 1970s and multiple flybys from the 1990s to the 2000s.

The first photographs of Ganymede from space were taken by Pioneer 10 flying past Jupiter in December 1973 and by Pioneer 11 flying by in 1974. Thanks to them, more accurate information about the physical characteristics of the satellite was obtained (for example, Pioneer-10 specified its dimensions and density). Their images show details as small as 400 km. Pioneer 10 closest approach was 446,250 kilometers.

Voyager spacecraft

In March 1979, Voyager 1 passed by Ganymede at a distance of 112 thousand km, and in July - Voyager 2 at a distance of 50 thousand km. They transmitted high-quality images of the satellite's surface and carried out a series of measurements. In particular, they specified its size, and it turned out that this is the most large satellite in the solar system (previously considered the largest satellite of Saturn, Titan). The current hypotheses about the geology of the satellite came from data from the Voyagers.

From December 1995 to September 2003, the Jupiter system was studied by Galileo. During this time, he approached Ganymede six times. The span names are G1, G2, G7, G8, G28 and G29. During the closest flyby (G2), Galileo passed 264 kilometers from its surface and transmitted a lot of valuable information about it, including detailed photographs. During the G1 flyby in 1996, Galileo discovered a magnetosphere near Ganymede, and in 2001, an underground ocean. Thanks to Galileo data, it was possible to build a relatively accurate model internal structure satellite. Galileo also transmitted a large number of spectra and found several non-glacial substances on the surface of Ganymede.

On its way to Pluto in 2007, New Horizons sent back visible and infrared photographs of Ganymede, as well as topographical and compositional information.

Proposed for launch in 2020, the Europa Jupiter System Mission (EJSM) is a joint NASA, ESA and Roscosmos program to study Jupiter's moons. In February 2009, it was announced that ESA and NASA had given it a higher priority than the Titan Saturn System Mission. For ESA, funding this mission is hampered by the fact that the agency has other projects that require funding. The number of vehicles that will be launched varies from two to four: Jupiter Europa Orbiter (NASA), Jupiter Ganymede Orbiter (ESA), Jupiter Magnetospheric Orbiter (JAXA) and Jupiter Europa Lander (Roskosmos).

One of the canceled missions to study Ganymede is the Jupiter Icy Moons Orbiter mission. For flight spaceship nuclear fuel would be used, which would be convenient for a more detailed study of Ganymede. However, due to budget cuts, the mission was canceled in 2005. Another proposed mission was called "The Grandeur of Ganymede" - "The Splendor of Ganymede".

On May 2, 2012, the European Space Agency (ESA) announced the start of the Jupiter Icy Moons Explorer (JUICE) mission in 2022, arriving in the Jupiter system in 2030. One of the main objectives of the mission will be the exploration of Ganymede, which will begin in 2033. Russia, through the involvement of the ESA, also intends to send a lander to Ganymede to look for signs of life and to conduct comprehensive studies of the Jupiter system as a typical representative of the gas giants.



Ganymede, the largest satellite of Jupiter, was found by the great Italian astronomer G. Galileo in 1610, simultaneously with three of his brothers. Since then 4 celestial bodies called the "moons of Galileo".

The German scientist S. Mariy also acted as a contender for the discovery. He claimed to have found satellites a year before Galileo, but he could not provide proof.

The discoverer designated the found satellites with numbers, although other astronomers (including S. Marius and I. Kepler) suggested names. One of them, associated with the names of those close to Jupiter (in Greek mythology, Zeus), was officially accepted, but only at the beginning of the 20th century.

Ganymede is the only moon with male name. According to legend, Zeus fell in love with the son of the Trojan king Ganymede and, turning into an eagle, took him to Olympus.

Fascinating facts about Ganymede

Ganymede is the largest of all satellites in our system. Its diameter is about 5270 km, and its mass is 1.45 * 1023 kg.

The satellite is removed from the planet by an average of 1 million km and bypasses it in 7.1 Earth days.

The celestial body includes a core of molten iron, a mountain mantle, and a thick (850–950 km) ice shell.

The density of the object, which is almost 2 g/cm3, suggests that the proportions of stone and ice in it are approximately the same.

There is a hypothesis that under the ice layer there is an ocean, the liquid in which is preserved due to the enormous pressure.

There are two types of relief on the surface of Ganymede. Ancient areas of dark color are covered with deep depressions (craters). Younger and lighter ones were formed as a result of tectonic processes.

It is assumed that about 4 million years ago the satellite was subjected to a powerful attack of asteroids.

Ganymede has a weak atmosphere with the presence of oxygen formed by melting ice.

The light emission above the satellite is weak, but there are also bright spots that create the effect of the northern lights.

Ganymede is unique in having a small magnetosphere connected to Jupiter's magnetosphere. This, to a certain extent, confirms the hypothesis of the presence of an underground ocean.

The largest satellite is an attractive object for scientists to search for life. Several probes sent to Jupiter also studied the features of Ganymede.

Since Ganymede in many ways resembles the Moon in its structure and features, scientists consider it as a possible object for colonization. Several new projects are pending approval.

Jupiter's largest moon, Ganymede, is easy to find in the virtual sky. By purchasing it, you will receive a magnificent gift for yourself or an original surprise gift for a loved one.

> Ganymede

Ganymede- the largest satellite of the solar system from the Galileo group: a table of parameters with a photo, detection, research, name, magnetosphere, composition, atmosphere.

Ganymede is the largest satellite not only of the Jupiter system, but of the entire solar system.

In 1610 year Galileo Galileo made an amazing discovery, as he found 4 bright spots near the giant Jupiter. At first he thought that there were stars in front of him, but then he realized that he was seeing satellites.

Among them was Ganymede, the largest moon in the solar system, larger than Mercury. It is also the only moon with a magnetosphere, an oxygen atmosphere, and an internal ocean.

Discovery and name of the moon Ganymede

In Chinese records, one can find a note that Ganymede could still be observed by Gan De in 365 BC. But nevertheless, the discovery is attributed to Galileo, who on January 7, 1610 successfully sent the device into the sky.

Initially, all satellites were called Roman numerals. But Simon Marius, who claimed to have found the moons on his own, offered his own names, which we still use today.

In the myths of ancient Greece, Ganymede was the child of King Tros.

Size, mass and orbit of the moon Ganymede

With a radius of 2634 km (0.413 Earth), Ganymede is the largest moon in our system. But the mass is 1.4619 x 10 23, which hints at a composition of water ice and silicates.

The eccentricity index is 0.0013 and the distance fluctuates between 1,069,200 km and 1,071,600 km (average 1,070,400 km). Spends 7 days and 3 hours on the orbital passage. Stays in a gravitational block with the planet.

Thus, you learned which planet Ganymede is a satellite of.

The orbit is inclined to the planetary equator, which causes orbital changes from 0 to 0.33°. The satellite is tuned to a 4:1 resonance with Io and a 2:1 resonance with Europa.

The composition and surface of the moon Ganymede

The density index of 1.936 g/cm 3 hints at the presence of the same proportions of stone and ice. Water ice reaches 46-50% of the lunar mass (below Callisto) with the possibility of ammonia formation. Surface albedo - 43%.

An ultra-infrared and UV survey showed the presence of carbon dioxide, sulfur dioxide, as well as cyanogen, hydrosulfate and various organic compounds. Later studies have found sodium sulfate and magnesium sulfate that may have come from the subsurface ocean.

Inside, Jupiter's moon Ganymede has a core (iron, liquid iron layer and sulfide outer), a silicate mantle and a shell of ice. It is believed that the core extends within a radius of 500 km, and the temperature is 1500-1700 K with a pressure of 10 Pa.

The presence of a core of liquid iron and nickel is hinted at by the moon's magnetic field. Most likely, the reason is convection in liquid iron with a high level of electrical conductivity. The core density index reaches 5.5-6 g/cm 3 , and for the silicate mantle it reaches 3.4-3.6 g/cm 3 .

The mantle is represented by chondrites and iron. The outer ice crust is the largest layer (800 km). There is an opinion that a liquid ocean is located between the layers. Aurora may hint at this.

Two types of relief are noted on the surface. These are ancient, dark and cratered areas, as well as young and light areas with ridges and grooves.

The dark part occupies 1/3 of the entire surface. Its color is due to the presence of clay and organic materials in the ice. It is believed that the whole thing is in crater formations.

The corrugated landscape is tectonic, which is associated with cryovalvanism and tidal heating. The kink could raise the temperature inside the object and push against the lithosphere, causing faults and cracks to form that destroyed 70% of the dark terrain.

Most of the craters are concentrated in dark areas, but they can be found everywhere. It is believed that 3.5-4 billion years ago, Ganymede went through a period of active asteroid attack. The ice crust is weak, so the depressions are flatter.

There are ice caps with ice discovered by Voyager. Data from the Galileo apparatus confirmed that they were most likely formed from plasma bombardment.

The atmosphere of the moon Ganymede

Ganymede has a thin layer of oxygen. It is created due to the presence of water ice on the surface, which is divided into hydrogen and oxygen upon contact with UV rays.

The presence of the atmosphere leads to the effect of an airbrush - a weak light emission created by atomic oxygen and energy particles. It is devoid of uniformity, so bright spots form over the polar territories.

The spectrograph found ozone and oxygen. This hints at the presence of the ionosphere because oxygen molecules are ionized by electron impacts. But this has not yet been confirmed.

The magnetosphere of the moon Ganymede

Ganymede is a unique satellite because it has a magnetosphere. The value of the stable magnetic moment is 1.3 x 10 3 T m 3 (three times higher than that of Mercury). The magnetic dipole is set at 176° relative to the planetary magnetic moment.

The strength of the magnetic field reaches 719 Tesla, and the diameter of the magnetosphere is 10.525-13.156 km. Closed field lines are located below 30° latitude, where charged particles are captured and form a radiation belt. Among the ions, single ionized oxygen is the most common.

The contact between the lunar magnetosphere and the planetary plasma resembles the situation with the solar wind and the Earth's magnetosphere. The induced magnetic field hints at the existence of an underground ocean.

But the possibility of a magnetosphere is still a mystery. It seems that it is formed due to the dynamo - the movement of material into the core. But there are other dynamo bodies that do not have a magnetosphere. It is believed that orbital resonances may serve as the answer. Increasing tidal heat can insulate the core and prevent it from cooling. Or the whole thing is in the residual magnetization of silicate rocks.

Habitability of the moon Ganymede

Jupiter's moon Ganymede is an attractive target for the search for life because of a possible subsurface ocean. An analysis in 2014 confirmed that there may be multiple oceanic layers separated by ice sheets. Moreover, the lower one touches the rocky mantle.

This is important, as heat from tidal flexing can enter the water to support life forms. The presence of oxygen only increases the odds.

Exploration of the satellite Ganymede

Several probes were sent to Jupiter, so they also tracked the features of Ganymede. Pioneer 10 (1973) and Pioneer 11 (1974) were the first to fly. They provided details of the physical characteristics. They were followed by Voyagers 1 and 2 in 1979. In 1995, Galileo entered orbit, studying the satellite from 1996-2000. He was able to detect a magnetic field, an internal ocean, and provide many spectral images.

The last review was in 2007 from New Horizons flying towards Pluto. The probe created topographic and compositional maps of Europe and Ganymede.

There are several projects currently pending approval. In 2022-2024 could launch a JUICE that would cover all of the Galilean moons.

Among the canceled projects is JIMO, which is going to study in detail the largest moon in the system. The reason for the cancellation is lack of funds.

Colonization of the moon Ganymede

Ganymede is one of the great candidates for a colony and transformation. This is a large object with a gravity of 1.428 m/s 2 (reminiscent of the moon). This means that the launch of the rocket will take less fuel.

The magnetosphere will protect against cosmic rays, and water ice will help create oxygen, water, and rocket fuel. But not without problems. The magnetosphere is not as dense as we are used to, so it will not be able to protect Jupiter from radiation.

Also, the magnetosphere is not enough to keep a dense atmospheric layer and a comfortable temperature. Among the solutions is the possibility of creating a settlement underground, closer to the ice deposits. Then we are not threatened by rays and frosts. So far, these are just drafts and sketches. But Ganymede deserves close attention, because one day it may become a source of life or a second home. The map will reveal the details of Ganymede's surface.

Click on the image to enlarge it

Group Amalthea	· · ·
Galilean satellites	· · ·
Group Themisto
Group Himalaya	· · · ·
Group Ananke	· · · · · · · · · · · · · · · ·
Group Karma	· · · · · · ·