Satellite cameras of the Galileo probe in 1997

Jupiter's moon Ganymede is the largest moon in our planet. solar system. It is larger than Mercury and Pluto, its diameter is three-quarters that of Mars. If it orbited the Sun instead of orbiting Jupiter, it would easily be classified as a planet.

Ganymede, consists of three main layers. A metallic iron core in the center (it generates a magnetic field), a spherical shell - a mantle that surrounds the core and the ice crust. The ice shell outside is very thick, about 800 km wide. Although the moon's surface is mostly ice, it may contain some rocks. The magnetic field is located inside the magnetosphere of massive Jupiter.

Image from a distance of about 70,000 km.

Characteristic

Opening date 1610
Weight 1.48 10*23 kg.
Equatorial radius 2631 km.
Average density 1.94 g/cm3
The average distance to Jupiter is 1.07 million km.
Rotation period 7.154553 days
Medium orbital speed 10.88 km/s
Orbital eccentricity 0.002
Orbital inclination 0.195 degrees
Second space velocity 2.74 km/s
Geometric albedo 0.42

Astronomers using space Hubble telescope, discovered a thin atmosphere of oxygen in 1996. The atmosphere is too thin to support life, especially since it is quite cold.

Surface relief

Space photos of Ganymede show that the moon has a complex geological history. The landscape is a mixture of two types of terrain. Forty percent is covered in craters and dark areas, while the remaining sixty percent is covered in light relief that forms complex patterns.

Image from a distance of about 4500 km

The geological term "furrow" is often used to describe a surface feature. These furrows are probably formed by faults or ejections of water from underground. The ridges reach a height of seven hundred meters and stretch for thousands of kilometers. The dark areas are old and rough, and are considered untouched areas of the bark.

Large craters almost do not rise and are rather flat. They do not have a central depression characteristic of craters on the Moon. This is probably due to the slow and gradual movement of the soft ice surface. There are bright and dark rays of ejecta around the craters.

Satellite discovery

This largest moon was discovered by Galileo Galilei on January 7, 1610. Along with Jupiter's three other moons, this was the first time a moon had been discovered around another planet. Galileo's discovery of the four keys eventually led to the understanding that the planets in our solar system orbit the sun.

But also throughout the 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 more mass 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 satellites of Jupiter, Ganymede's rotation is tidally synchronized with its orbital movement, so that it is turned to Jupiter with 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 bears and clear traces 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 ultraviolet light 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, in one cubic centimeter of air at normal conditions(0C, 1 atm.) contains 2.68 * 10 19 molecules (so that the atmosphere of Ganymede has a density comparable to that of earth air, it will have to be compressed into a layer with a thickness of ~0.4 µm). 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 intensity magnetic field 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).
AT this moment There are 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:
Major axis orbits 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 free fall on the surface: 1.42 m/s 2 (about 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

> Ganymede

Ganymede- most large satellite Solar system from the Galileo group: table of parameters with photos, detection, exploration, 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 amazing discovery, since I 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's the same single moon with a magnetosphere, an oxygen atmosphere, and an inland ocean.

Discovery and name of the moon Ganymede

AT Chinese records you can find a mark 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 myths 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 high level 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 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

There is a weak one on Ganymede atmospheric layer with 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 - 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 stable magnetic moment- 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 planetary plasma resembles the situation with 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 physical characteristics. They were followed by Voyagers 1 and 2 in 1979. In 1995, Galileo entered orbit, studying the satellite from 1996-2000. He managed to detect a magnetic field, inland 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 largest moon in 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. it large object with gravity 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	· · · · · · ·

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

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

Surface

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

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

Later pictures showed possible presence liquid water on Ganymede.

Magnetic field and magnetosphere of Ganymede

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

Orbit, theory of motion, ephemeris

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

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

Rotation

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

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

Most major satellite in the Jupiter system and in the solar system in general, they were 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, average density Ganymede only ρ \u003d 1.93 g / cm 3: there is a lot of ice on the satellite. Lots of multiples ditch, covering areas of dark brown color, 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. Between the mantle and the crust is possible liquid water under great pressure, the pressure allows very low temperature water to be in the liquid phase.

Surface comparison of Ganymede (left) and Europa (right). NASA