Dawning Academy, inside the dungeon, mimic classroom.

Hua Feng and Yun Meng, and Bai Feng stood side by side, with Ganymede above their heads in the air, as if they were real.

Callisto, also known as Callisto, is a moon orbiting Jupiter that was first discovered by Galileo Galilei in 1610. Europa is the third largest moon in the solar system and the second largest moon of Jupiter, after Ganymede.

Calmede is 99% the diameter of Mercury, but only one-third the mass. The satellite's orbit is the farthest of the four Galilean moons from Jupiter, about 1.88 million kilometers. Ganymede is not in orbital resonance like the three Galilean moons (Europa, Europa, and Callisto) in the inner layer, so there is no significant tidal heat effect. Ganymede is a synchronously rotating moon that always faces Jupiter on the same side. Due to its farther orbit, Callisto's surface is less affected by Jupiter's magnetic field than its inner moons.

Callisto is made up of nearly equal amounts of rock and water, with an average density of about 1.83 g/cm. Astronomers have known that Callisto's surface material includes ice, carbon dioxide, silicates, and various organic matter. Galileo's findings indicate that Callisto may have a small silicate core within it, and that there may be an underground ocean of liquid water 100 kilometers below its surface.

Due to the possible presence of oceans on Callisto, there may also be organisms on this moon, but less likely than another nearby moon, Europa. The moon has been explored by several space probes, including Pioneer 10, Pioneer 11, Galileo Galileo, Jupiter and Cassini. It has long been considered that Europa is the best place to set up a base for further exploration of the Jupiter system.

The surface of Europa has been hit hard and is very old. Because there is no evidence of geological activity on Callisto, such as plate movements, earthquakes, or volcanic eruptions, astronomers believe that its geological features are mainly caused by meteorite impacts. Callisto's main geological features include multi-ring structures, various forms of impact craters, crater chains, cliffs, ridges, and sedimentary topography.

Astronomers have carefully examined the moon's surface topography and found that the surface topography of the satellite is variable, including small, bright ice deposits at the top of the uplifted terrain and areas with gentler edges (made up of darker material) around it. Astronomers believe that this topography is the result of the sublimation of small geological formations, the general disappearance of small impact craters, and the fact that many of the pimpled terrain are traces of the remains, the exact age of which has not yet been determined.

Callisto has a very thin atmosphere, composed mostly of carbon dioxide, possibly oxygen, and a highly active ionosphere. Scientists believe that Europa was formed slowly by the accretion of the gas and dust disks around Jupiter. Due to the slow formation of Europto and the lack of tidal heat effects, the internal structure does not undergo rapid differentiation. Thermal convection within Callisto began soon after its formation, and this convection led to a partial differentiation of the internal structure, possibly the formation of subsurface oceans and relatively small rock cores at depths of 100 to 150 km above the surface.

Italian astronomer Galileo Galilei discovered Callisto and three other large moons of Jupiter (Europa, Europa, and Callisto) in January 1610. Callisto's name comes from Calisto, one of Zeus's lovers in Greek mythology, a nymph (sometimes also believed to be the daughter of Lycaon) who was closely related to Artemis, the goddess of the moon.

Simon Marius suggested the name shortly after the star was discovered, while Marius believed it was Johannes Kepler's suggestion. However, astronomers did not welcome the name for a long time, and it was not widely adopted until the mid-20th century. Many early astronomical texts refer to the moon in Roman numerals (a system developed by Galileo) as Jupite

IV) or "Jupiter's fourth moon" (the fou

th satellite of Jupite

）。

Near-infrared spectra of an impact crater plain on Callisto. Calmede has an average density of 1.83 g/cm³, suggesting that it is composed of nearly equal amounts of rock and ice water, in addition to the possible presence of some unstable ice bodies, such as ammonia. The specific gravity of the ice body is between 49-55%.

The exact composition of the Ganymede rocks is unknown, but it is likely to be close to the L-type or LL-type common chondrites, which contain less all-iron and metallic iron and more iron oxides than H-chondrites. On Callisto, the abundance ratio of iron and silicon is 1.05-1.27 by mass, while in the Sun, it is 1.8.

The surface of Ganymede is asymmetrical: its co-orbital side is darker than the counter-orbital side, which is the opposite of other Galilean moons. In addition, the counter-orbital side appears to be rich in carbon dioxide, while the co-orbital side contains more sulphur dioxide. Many of the younger impact craters on Callisto are rich in carbon dioxide. In general, the material composition of Calymede's surface, especially in the dark zone, is very similar to that of a D-type asteroid, whose surface is made of carbon-based material.

The albedo of the surface of Ganymede is 0.2. It has been speculated that the material composition of its surface is roughly the same as that of its whole. Using near-infrared spectroscopy, scientists have found intense adsorption bands of ice water in the wavelengths of 1.04, 1.25, 1.5, 2.0 and 3.0 microns.

Ice is ubiquitous on the surface of Callisto, with a gravity of between 25-50%. Analysis of high-resolution near-infrared and ultraviolet photographs taken by Galileo and ground-based observatories revealed a variety of insoluble substances such as magnesium- and iron-containing hydrated silicates, carbon dioxide, sulfur dioxide, and possibly ammonia and a variety of organic compounds. [Spectral analysis data indicate that even in a small area, the material composition of the star's surface is extremely mixed.] Small, bright patches of ice are mixed with patches of rocks and ice, while vast dark areas are made up of non-icy material.

Diagram of the internal structure of Europa. Beneath the surface of Callisto's heavy bombardment is a layer of cold, hard icy lithosphere with a thickness of between 80 and 150 kilometers.

Studies of the magnetic field surrounding Jupiter and its moons show that there is a saltwater ocean 50-200 kilometers below Callisto's crust: scientists have found that Ganymede placed in Jupiter's variable magnetic field is like an ideal conductive sphere, that is, the magnetic field cannot penetrate to reach the inner core of the moon, which means that there is a layer of highly conductive liquid with a thickness of at least 10 kilometers in the star. The ocean may also contain small amounts of ammonia or other antifreeze substances, up to 5% specific gravity, preventing the ocean from freezing. In this case, the thickness of the ocean will reach 250-300 km. In the absence of the ocean, its icy lithosphere would be much thicker, perhaps up to 300 kilometers thick.

The interior of the lithosphere and the stellar beneath the putative ocean may be neither homogeneous nor completely differentiated. Galileo's sounding data, in particular the dimensionless moment of inertia measured in a close-range flyby of 0.3549 ± 0.0042, indicate that the interior is composed of compressed rock and ice, and that the proportion of the rock increases with depth due to the partial deposition of the constituents. That is, the internal structure of Europa is only partially layered. At this density and moment of inertia, a small silicate core may be present in the center of the star. The radius of such cores cannot exceed 600 km, while their densities may be between 3.1-3.g/cm³.

The geological age of the surface of Ganymede is very old, and it is also one of the most heavily bombarded objects in the solar system, and its crater density is close to saturation: any new crater may overlay the old one. The large geological formations on Callisto are relatively simple: there are no large mountains, volcanoes, or other endogenous tectonic features. Impact craters and multi-ring structures, as well as fissures, cliffs, and sedimentary terrain, are among the few large geological formations found on the surface of the star.

The surface of Europa can be divided into several different geological units: crater plains, brighter plains, bright and gentle plains, and multiple types of topographic units consisting of multi-ring structures and craters. The crater plain, which covers most of Callisto's surface, is typical of the ancient lithosphere, composed of a mixture of ice and rock.

Bright craters, remnants of ancient craters known as residual structures, and central portions of multi-ring structures exist in the brighter plains, which scientists speculate were deposited by icy craters. The bright, gentle plains cover a small area and are often found in the ridges and grooves of the Volhalla crater and the Asgard crater, as well as isolated spots in the crater plains.

The formation of this topography was initially thought to be related to endogenous geological activity, but high-resolution photographs returned by Galileo show that this bright, gentle plain terrain is associated with fractured, nodulous terrain and does not show any signs of multiple overlying of the surface of the star. Photographs of Galileo also show small patches of dark, flat areas on Callisto covering less than 10,000 square kilometers and surrounded by the surrounding terrain. This terrain may be glacial volcanic sedimentary terrain. These brighter or gentler plains are of slightly younger geological age than the crater plains.

The crater on Callisto ranges in diameter from 100 meters — the maximum resolution of a sounding photograph — to more than 100 kilometers, while multi-ring structures are not listed. Smaller impact craters with a diameter of less than 5 km have a simple bowl structure or a flat-bottomed structure. Impact craters with diameters between 5 and 40 km have a central peak.

Many impact craters with diameters between 25 and 100 km, such as the Tyndall impact crater (Ti

d

c

ate

), whose central peak is replaced by a collapsed terrain. Large impact craters with diameters greater than 60 km may have arched structures in the center, which may have been caused by tectonic uplift after the impact event. A small number of bright craters with a diameter of more than 100 km have distinctive arch structures. These craters are shallower than their lunar counterparts and may be a transition to a multi-ring mechanism.