Satellite Ganymede: history of discovery, physical characteristics. Satellite of the planet Jupiter
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 and are 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 could not provide evidence.
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 mountainous 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.
The uniqueness of Ganymede lies in the presence of 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.
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 size of a planet, 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 Jupiter's largest moon
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 solar system, having 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 parts rocks 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 - a highly rarefied, but still oxygen atmosphere. Oxygen appears in it due to the presence of water ice deposits on the surface of the satellite, under the action 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 beautiful and suggests thoughts of colonization and extraterrestrial intelligence, it is worth remembering that the pressure of Ganymede's atmosphere 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 value of the stable magnetic moment of which reaches -1.3 x 10 3 T m 3 (ie, 3 times higher than that of Mercury). The strength of the magnetic field reaches 719 Tesla, and the diameter of the magnetosphere reaches 13156 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.
When the magnetosphere of Ganymede and the plasma of Jupiter come into contact, a situation is observed very similar to the contact of the 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.
On the this moment there are still a lot of unresolved questions about Jupiter's moons, 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 reserves, some kind of 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 make a complete revolution 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 a central core with a radius of 500 km, silicate rocks, a mantle and a 900 km layer of ice. Core consists of molten iron and has a density of approximately 5500 kg/m³. In the liquid core of Ganymede, active chemical movements occur and due to this, 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 intermittent 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 all celestial bodies with a thin atmosphere, Climate on Ganymede almost indistinguishable from . Minimum temperature is -200 °C, and in the daytime, the satellite can warm up to -120 °C with the sun's rays. The gas envelope around the satellite consists entirely of oxygen, and has a pressure of 1-2 μPa (10 11 times less than 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
3.45 times bigger moon and 14.25 less than 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, according to various 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 apparatus "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 no large mountains or volcanoes were noticed on it, 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,
to the fact that such waves were formed from the impact force of a 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.
The largest satellite in the Jupiter system and in general in the solar system was named after Ganymede, the son of the Trojan king, abducted by Zeus to Olympus, where he began to distribute nectar to the gods.
The radius of the satellite is 2631 km. It is larger than Mercury in diameter. However, the average density Ganymede only ρ \u003d 1.93 g / cm 3: there is a lot of ice on the satellite. Lots of multiples moat covering areas dark Brown, testifies to the ancientit, about 3-4 billion years, the age of this surface. The younger sections covered with systems of parallel grooves formed by lighter material in the process of stretching the ice crust. The depth of these furrows is several hundred meters, the width is tens of kilometers, and the length can reach up to several thousand kilometers. Some Ganymede craters have not only light ray systems (similar to the moon), but sometimes dark ones.
Outwardly, according to photographs, Ganymede resembles the Moon, but it is much larger than it. 40% of the surface of Ganymede is an ancient thick ice crust covered with craters. 3.5 billion years ago, strange areas covered with furrows appeared on it. Huge impact craters on the surface of Ganymede were formed during the era of the formation of satellites and planets. Young craters have a bright bottom and expose the icy surface. Ganymede's crust is made up of a mixture of ice and dark rocks.
The internal structure of Ganymede is supposedly as follows. In the center of the satellite is either a molten iron core or a metal-sulfur core surrounded by a mantle of rocks. Next comes a thick layer of ice about 900 km thick. and it already has a satellite crust. High pressure liquid water is possible between the mantle and the crust, the pressure allowing very low temperature water to be in the liquid phase.
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Surface comparison of Ganymede (left) and Europa (right). NASA |
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 more mass Europa 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 mass 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 |
| 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 perturbations 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 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 brown surface there are a large number of light 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 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.
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 Ganymede's higher internal temperature to tidal heating or more intense exposure to late 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 thermal 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 in a lower total iron content, a lower content metallic iron and large - iron oxides. 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 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. 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. 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.
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| 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. |
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| 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. |
| SC "GALILEO": GANIMED |
Numerical modeling of the interior of the satellite, 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 different types(ice I, III, V, VI). The number of liquid interlayers possibly reaches 4; their salinity increases with depth.
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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. |
| SC "GALILEO": GANIMED |