Ganymede
Ganymede is the largest of the Galilean moons and the second largest moon in the solar system. In size, it is located between Mercury and Mars. Its diameter was determined by covering the star with an accuracy of 10 - 20 km, the average density, equal to 1.95 g/cm3, is known with an accuracy of several percent. The main uncertainty in this quantity arises from the fact that a significant atmosphere can exist on this satellite. If the surface pressure is greater than 10-3 mbar, then the diameter determined during coating will refer to some level in the atmosphere, and not to a solid surface, and the density given above will be the lower limit of the solid density. However, in theory the existence of such an atmosphere is doubtful. But we will have to consider the above figures as the diameter, but at the same time we will keep in mind that the true diameter may be somewhat smaller.
It, like Calisto, consists of water, but its bowels are completely differentiated. This may be due to its greater proximity to Jupiter and a slightly higher abundance of radioactive elements, which is possible due to its higher density. Models of the internal structure of this satellite assume a rocky core surrounded by a liquid water mantle with a thin (100–200 km) ice crust. It is believed that about 15% of the mass is contained in the core, which consists mainly of silicates and metal oxides, so we can assume that only a small amount of CH and NH3 is dissolved in water.
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Ganymede was the first natural satellite, apart from the Moon, to be explored using radar. Goldstein Morris observed the reflection from the satellite at a wavelength of 12.6 cm for six nights. The dispersion coefficient turned out to be 12%, i.e. it is at least as large as any terrestrial planet, at this wavelength the roughness of Ganymede is more significant than that of the rest of the terrestrial planets.
So, Ganymede is a planet-like satellite, mainly consisting of water (probably in a liquid state), containing a core of rocky substances and a crust of ice (frozen water). Its surface is covered with approximately equal patches of ice and stony matter of unknown mineralogical composition and probably has the appearance of loose regolith supported by meteorite impacts and evaporation of hoarfrost. Ice and rocky matter are most likely not mixed, but distributed in separate spots, with a slightly higher concentration of ice in the forward hemisphere. It is possible that Ganymede has an atmosphere with a surface pressure between 10-3 and 1 mbar, in which NH3 and CH are non-primary gases. But the evidence for the existence of an atmosphere is not indisputable. In view of the low strength of the ice crust on Ganymede, one can hope to detect only very recently formed large-scale relief elements.
