In the brilliant starry sky where the stars flowed, Hua Feng saw that the largest impact terrain on Ganymede was the multi-ring basin. The Volhalla crater is the largest of two enormous ones, with a bright central zone that reaches 600 kilometers in diameter and a ring structure that continues to extend outward for 1,800 kilometers. The second largest multi-ring structure is the Asgard Crater, which is about 1,600 kilometers in diameter.

Polycyclic structures may be caused by concentric ring-like faults in soft or flowing material, such as the lithosphere above the ocean, after an impact event. A chain of craters is a long chain of craters distributed in a straight line on the surface of a star, which may have been formed by Callisto being hit by a celestial body that was too close to Jupiter and disintegrated by gravitational tides, or it could have been impacted at a small angle. The former was confirmed by the impact of the comet Shoemaker-Levy 9.

As mentioned earlier, Calymede also has a patchy terrain of pure ice with an albedo of up to 0.8, surrounded by darker material. High-resolution photographs of Galileo show that these brighter patches are mainly located on uplifted terrain: crater craters, cliffs, ridges, and nodules. This plaque may be a thin layer of frost deposits. Darker materials are usually located in the surrounding low-lying and flatter areas, such as the low-lying areas between the bottom and the crater, which cover the original frost sediments, so that the area appears darker, forming dark spots with a diameter of more than 5 km.

At a level of several kilometers, Callisto's surface topography shows more degraded features than the surface of other Galilean moons. For example, compared to the dark zone of other satellites, such as Europa, the surface of Europa lacks impact craters less than 1 km in diameter, and instead is replaced by the ubiquitous small nodules and craters.

The nodulous terrain is thought to be the remnant of the crater's crater margin after a hitherto unknown degradation process, most likely caused by the slow sublimation of the ice, which is when Callisto reaches the sunset point, when the temperature on the sunny side reaches more than 165 K, at which point the ice sublimation: the bedrock causes the dirty ice on it to decompose, causing the ice water and other volatile substances to sublimate in it. The non-icy remnants of the wreckage collapsed and fell down the slope of the crater rim. Such collapses often occur near and inside the crater and are referred to as "perimeter debris" (DEB).

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In addition, some of the craters have their craters whose rims are cut by a number of winding, canyon-like cuts (they are called ravines) that look a bit like canyons on the surface of Mars. In the ice sublimation hypothesis, the dark material located in the low-lying area is interpreted as a cover consisting mainly of non-icy material from the crater rim of a degraded impact crater, which covers most of the ice bedrock on the surface of Europa.

The relative age of the collapse and nodules can be inferred from the density of the craters covered by the geological units: the greater the density of the crater distribution, the greater the relative age of the geological unit. Their absolute age is uncertain, but theoretical projections suggest that the geological age of the crater plain is thought to be 4.5 billion years old, almost dating back to the formative days of the solar system. The geological age of the multi-ring structure and the crater depends on the crater density in the area in which it is located, and the estimated age varies from 1 billion to 4 billion years.

The induced magnetic field around Callisto has a very thin atmosphere, mostly made of carbon dioxide. The Near-Infrared Mapping Spectrometer (Nea

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, NIMS) at 4.2 microns, confirming its existence. It is estimated to have a surface pressure of 7.5 × 10⁻¹² bar and a particle density of 4 × 10⁸ cm⁻³. This layer of the atmosphere is so thin that it takes only four days for the material that makes it to escape, so the atmosphere must have been replenished continuously, probably from dry ice sublimated from the star's icy crust, which is also consistent with the hypothesis of ice sublimation formation in the nodulous terrain of the bright area of the star's surface.

The ionosphere of Ganymede, first discovered during several flyby flights by Galileo, has a high electron density of 7-17 × 10⁴ cm⁻³, which is incompatible with the photoionization of atmospheric carbon dioxide. So it has been predicted that the component of Callisto's atmosphere should be oxygen (10 to 100 times that of carbon dioxide), but the presence of oxygen has not yet been detected in this atmosphere.

Ganymede (bottom left), Jupiter, and Europa (located in the lower left of Jupiter's Great Red Spot). Europa is the farthest moon from Jupiter, Galileo, with an orbit of about 1.88 million kilometers (26.3 times Jupiter's radius of 71,398 kilometers), much farther than the 1.07 million kilometers radius of Jupiter's next closest moon. Due to the large radius of the orbit, it is not in orbital resonance and probably never will.

Ganymede does not participate in orbital resonance, which means that it will never produce significant tidal heat effects, which are important drivers of structural differentiation and development within stars. Because of its distance from Jupiter, the flow of charged particles from Jupiter's magnetic field on its surface is weak—300 times weaker than that on Europa's surface. Therefore, compared to several other Galilean moons, the photoosmotic effect of charged particles on the surface of Ganymede is weak.

Like most satellites, Europa is a synchronously rotating satellite, meaning that Calisto has a rotation period equal to its orbital period, which is about 16.7 Earth days. The eccentricity of its orbit is very small, and the inclination of its orbit is also very small, close to the equator of Jupiter, and the eccentricity and inclination of the orbit are also affected by the gravitational perturbations of the Sun and Jupiter as a function of periods over hundreds of years. The variation ranges are 0.0072-0.0076 and 0.20-0.60°, respectively. This change in orbit allows the inclination of its shaft to vary between 0.4-1.6°.

Partial stratification of Callisto's internal structure, which is inferred from dimensionless moment of inertia, indicates that the star was never sufficiently heated to melt its icy portion. Therefore, the most likely model for its formation is the slow accretion process in the low-density Jupiter sub-nebula.

This long-lasting accretion process causes the star to eventually cool down and unable to retain the heat accumulated during the accretion process, the decay process of radioactive elements, and the contraction of the star, thus blocking the process of ice melting and rapid differentiation. The time taken to form is between 100,000 and 10 million years.

The further evolution of Calmede depends on the competition between the heat production mechanism of radioactive decay and the cooling mechanism of heat conduction close to the surface of the star, and whether the interior of the star is in a state of solid or sub-solid convection. The specific motion of the sub-solid convection of the ice is the largest uncertainty factor in all ice satellite models.

Based on the effect of temperature on the viscosity of ice, sub-solid convection occurs when the temperature is close to the melting point of the ice. In sub-solid convection, the ice moves very slowly, about 1 cm/year, but in the long run, sub-solid convection is in fact a very effective cooling mechanism. On Callisto's cold, hard surface – known as the "sealing cap" (stag

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t lid) – where heat is not conducted in the form of convection, in the ice beneath this layer, heat is conducted in the form of sub-solid convection.

For Callisto, the outer conductive layer is a cold, hard lithosphere about 100 kilometers thick. Its presence explains why there is no sign of endogenous tectonic activity on the surface of Callisto. Within Callisto, thermal convection may be hierarchical, as at high pressures, ice water appears in a variety of phases, from the first state of ice on the surface of the star to the seventh state of ice at the center of the star.

In the early days, the operation of Ganymede's internal sub-solid convection mechanism prevented the massive melting of the ice mass, which in turn led to the differentiation of the star's interior, resulting in the formation of a large rocky core and icy mantle. At the same time, due to the presence of convection, the partial differentiation of ice and rock has continued for billions of years and is still slowly going on today.

The present explanation for the formation of Calmede takes into account the possibility of an underground ocean beneath its surface, the formation of which is related to an anomaly in the melting point of the first crystalline phase of the ice body, whose melting point decreases with increasing pressure, and can be as low as 251 K at a pressure of 2070 bar.

In all real-world models of Callisto, the temperature of the strata at depths of 100-200 kilometers is very close to or even slightly exceeds this anomalous melting point. The presence of a small amount of ammonia – about 1-2% – increases the likelihood of the presence of a liquid at this depth, as ammonia further lowers the melting point of ice.

Although Callista and Europa are similar in many ways, the geological history of the former is relatively simple. Before the impact event and other external forces, the surface of the star was basically formed. In contrast to Callisto, a neighboring moon with grooved structures, few signs of tectonic activity have been found on Callisto.

This relatively simple geological history is of great significance to planetary scientists, who can use the star as a good basic reference against other, more complex stars.

Artistic imagination of the base set up by humans on Callisto in the future[40]In the 70s of the 20th century, Pioneer 10 and Pioneer 11 approached Jupiter successively, and obtained a small amount of new information about Callisto. The real breakthrough came from the expeditions of Voyager 1 and Voyager 2 between 1979 and 1980.

They photographed more than half of Callisto's surface with an image resolution of between 1-2 kilometers, while also accurately measuring Callisto's surface temperature, mass, and size. The second wave of expeditions took place between 1994 and 2003, when Galileo flew by Calilyo eight times at close range, with the last flyby taking place in 2001 when Galileo was in orbit at C30, just 138 kilometers from the surface of Callisto. Galileo completed a global mapping of the surface of Ganymede and sent back a large number of photographs of specific areas with a resolution of 15 meters.

In 2000, Cassini conducted high-precision infrared spectroscopic surveys of four Galileo satellites, including Europa, on its way to Saturn. In February-March 2007, the New Horizons probe passed by Ganymede on its way to Pluto, photographing and spectroscopy.