Chapter 1638: Ganymede terrain

Chapter 1826: Ganymede Terrain
Ganymede is the largest moon in the solar system. The diameter is larger than Mercury, and the mass is about half of Mercury.
Ganymede is mainly composed of silicate rocks and icy bodies. The stars are clearly layered and have an iron-rich, fluid core. It is larger than Mercury and is the only known satellite in the solar system with a magnetic circle.
Ganymede was not first discovered by Galileo. Between 400 B.C. and 360 B.C. (most likely in the summer of 364 B.C.), according to the "Tang Kaiyuan Zhanjing" quoted by Gan De when talking about Jupiter: "If there is little red star attached On its side", the famous astronomy historian Mr. Xi Zezong pointed out: Gander observed Jupiter’s last moon Europa in the middle of the 4th century BC.
As for the discovery of Jupiter’s satellites, the discovery of the satellites of Jupiter in recent times was only discovered in 1610 after the invention of the telescope in the early 17th century by the great Italian scientist Galileo Galileo. But Gander had been Galileo for nearly two thousand years, and he discovered Jupiter's moons with the naked eye without a telescope. This is a miracle.
Later, the astronomer Simon Marius named it after Ganymedes, the lover of Zeus in Greek mythology. The Voyager spacecraft accurately measured the size of the satellite, and the Galileo probe discovered its underground ocean and magnetic field.
Ganymede is the only known satellite in the solar system that has a magnetic circle, which may be produced by the convective motion of an iron-rich flowing core. A few of the magnetic circles overlap with Jupiter's larger magnetic field, creating outwardly diverging field lines. Ganymede has a thin oxygen-containing atmosphere, which contains atomic oxygen, oxygen and ozone. At the same time, atomic hydrogen is also one of the components of the atmosphere. Whether Ganymede has an ionosphere has not yet been determined.
Ganymede is mainly composed of silicate rocks and icy bodies. The stars are clearly layered and have an iron-rich, fluid core. Scientists speculate that there is an ocean of salt water sandwiched between two layers of ice at 200 kilometers below the surface of Ganymede. There are two main topography on the surface of Europa: the darker area covers about one-third of the total area of ​​the astronomical body, which is densely covered with impact craters. The geological age is estimated to be 4 billion years old. The geological age of grooves and ridges is slightly younger than the former. The cause of the broken geological structure in the bright area is still a mystery, and it may be caused by tectonic activities caused by tidal heat.
Ganymede is the only known satellite in the solar system that has a magnetic circle. It has a thin oxygen-containing atmosphere, which contains atomic oxygen, oxygen and ozone. Whether Europa has an ionosphere has not yet been determined.
There are two main types of terrain on Europa’s surface: one is a very old dark area with dense impact craters, and the other is slightly younger than the previous one (but the geological age is still very old), with a lot of grooves and The bright area of ​​the ridge. The area of ​​the dark zone occupies about one-third of the total area of ​​the sphere, and it contains clay and organic matter, which may have been brought by the meteorite that hit Europa.
The heating mechanism that produces the grooved terrain is still a big problem in planetary science. The current view is that the trench topography is essentially formed by tectonic activities; and if ice volcanoes play a role in it, it is only a secondary role.
In order to cause this tectonic activity, Ganymede’s lithosphere must be subjected to strong enough pressure, and the force that caused this pressure may be related to the tidal heating that has occurred in the past-this effect may be in a different state in Ganymede. In a stable orbital resonance state, gravitational tides deflection on the ice body will heat the interior of the star, exert pressure on the lithosphere, and further lead to the formation of cracks, horst and graben. These topography replace the 70% surface area of ​​Ganymede. % Ancient dark area.
The formation of the groove topography may also be related to the formation process of the early inner core and the tidal heating inside the stellar body afterwards. The phase change and thermal expansion and contraction of the ice caused by them may lead to the slight expansion of Ganymede. It is 1-6%. As the star develops further, hot water jets are squeezed from the core to the surface of the star, causing structural deformation of the lithosphere. The thermal energy generated by the radioactive decay inside the stars is the most likely heat source, and the formation of Ganymede's underground ocean may depend on it. Through researching models, people found that if Ganymede's orbital eccentricity value was much higher than today's (in fact, it may be so), then tidal heat energy may be replaced by radioactive decay heat source and become Ganymede's main heat source.
It can be seen in both types of terrain, but it is more densely distributed in the dark area: this area has been bombarded by large-scale meteorites, so the distribution of impact craters is saturated. There are fewer impact craters in the brighter trench topography, where the land developed due to structural deformation is formed as the main geological feature. The density of impact craters indicates that the geological age of the dark zone has reached 4 billion years, which is close to the geological age of the highland terrain on the moon; while the trench terrain is slightly younger (but its exact age cannot be determined).
Similar to the moon, Ganymede experienced a period of heavy meteorite bombardment 3.5 to 4 billion years ago. If this is true, then there has been a large-scale bombardment event in the solar system during this period, and the bombardment rate after this period It is also greatly reduced in the bright area. There are both impact craters covering the trenches and trench cutting impact craters. This shows that some of the trenches are also very old in geological age.
There is also a relatively young impact crater on Ganymede, and its outward radiation is still clearly visible. The depth of the impact crater of Ganymede is not as deep as that on the Moon and Mercury. This may be due to the weak texture of the icy layer of Ganymede and displacement, which can transfer part of the impact force. Many geologically old impact crater crater structures It has disappeared, leaving only a remnant called a variable structure.
The salient features of Ganymede include a darker plain called the Galileo area. The grooves in this area are distributed in concentric rings, which may have formed during a period of geological activity. Another distinguishing feature is the two polar caps of Ganymede, which may be composed of cream.
This layer of frost extends to an area of ​​40° latitude. The Voyager first discovered Ganymede's polar cap. There are currently two theories explaining the formation of the polar cap. One is believed to be caused by the diffusion of ice at high latitudes, and the other is believed to be caused by the bombardment of plasma ice from outer space. Galileo’s observations are more inclined to the latter theory.
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