To Hua Feng's surprise, tidal heat can be seen in both terrains, but it is more densely distributed in the dark zone: this area has been subjected to large-scale meteorite bombardment, so the crater distribution is saturated.

There are fewer impact craters in the brighter trench terrain area, where the terrain developed due to tectonic deformation becomes the main geological feature.

The density of the craters indicates that the dark zone is 4 billion years old, which is close to the geological age of the upland terrain on the Moon, while the trench terrain is slightly younger (although its exact age cannot be determined). Similar to the Moon, 35-4 billion years ago, Europa experienced a period of violent meteorite bombardment, if this is true, then there was a large-scale bombardment event in the solar system during this period, and after this period, the bombardment rate was greatly reduced in the bright region, both the impact crater covering the groove and the groove cutting impact crater, which indicates that some of the grooves are also very old.

There are also relatively young impact craters on Europa, and their radiating radiation is still clearly visible. Calliste's craters are not as deep as those on the Moon and Mercury, which may be due to the fact that Callisto's ice strata are weak and can be displaced, allowing them to divert some of the impact forces

Callisto's distinguishing features include a darker plain known as the Galileo Zone, where grooves and gullies are arranged in concentric rings, probably formed during a period of geological activity. Another distinguishing feature is Ganymede's two polar crowns, which may be composed of frost. This layer of frost extends to an area of latitude 40°. Voyager discovered Callisto's polar crown for the first time. At present, there are two theories to explain the formation of the polar crown, one is that it is caused by the spread of ice at high latitudes, and the other is that it is caused by plasma ice bombardment in outer space. Galileo's observations are more inclined to the latter theory,

In 1972, a combined team of Indian, British, and American astronomers working at the Boscha Observatory in Indonesia announced that they had detected Europa's atmosphere during an occultation phenomenon, when Jupiter was passing in front of a star. They estimated its atmospheric pressure to be about 1 microbar (0.1 Pa).

In 1979, when Voyager 1 was passing by Jupiter, it made similar observations with the help of an occultation at that time, but obtained different results. The Voyager 1 occultation observation method uses a far-ultraviolet spectrum shorter than 200 nanometers, which is much more accurate in determining the presence or absence of gas than the visible spectrum observation method of 1972.

Voyager 1 observations indicate that there is no atmosphere on Callisto, and that the maximum density of particles on its surface is only 1.5 × 10⁹ cm³, corresponding to a pressure of less than 2.5 × 10⁵ microbars. The latter figure is five orders of magnitude smaller than the 1972 figure, suggesting that the early estimates were too optimistic.

False-colored temperature map on the surface of Europa, but in 1995 the Hubble Space Telescope discovered the presence of a rare, oxygen-based atmosphere on Callisto, similar to Europa's atmosphere. The Hubble telescope detected atmospheric light of atomic oxygen in the far-ultraviolet spectral region between 130.4 nm and 135.6 nm.

This atmospheric light is emitted when molecular oxygen is bombarded by electrons and dissociates, suggesting the existence of a neutral atmosphere dominated by O₂ molecules on Ganymede. The surface particle density ranges from 1.2 to 7 × 10⁸ cm³ and the corresponding surface pressure is 0.2-1.2 × 10⁵ microbar. These values are within the upper limit of the values that Voyager had detected in 1981. This trace concentration of oxygen is not enough to sustain life, and the source of this may be the process by which the ice on the surface of Ganymede decomposes into hydrogen and oxygen under the influence of radiation, with hydrogen quickly escaping from Ganymede due to its low atomic weight.

The atmospheric light observed on Europa is not spatially homogeneous like similar phenomena on Europa. The Hubble telescope has found several bright spots in the northern and southern hemispheres of Ganymede, two of which are located at 50° latitude, at the junction of the diffusion and aggregation field lines of the Ganymede magnetosphere. At the same time, it has been suggested that the bright spot may be the aurora formed by the plasma cutting the diffusion field lines during the fall.

The presence of a neutral atmosphere should also be in the ionosphere on Callisto, because oxygen molecules are ionized after being bombarded with high-energy electrons from the magnetosphere and the sun's far-ultraviolet radiation. But like the atmosphere, the nature of the Ganymede ionosphere has been controversial. Some of Galileo's observations found a high density of electrons on the surface of Europa, suggesting the presence of an ionosphere, but others found nothing. The electron density on the surface of Europa, as measured by various observations, ranges from 400-2,500 cm³. As of 2008, the parameters of the Ganymede ionosphere had not been precisely determined.

Another way to prove the existence of Calliste's oxygenated atmosphere is to measure the gases hidden in the ice on Callisto's surface. In 1996, scientists published measurements of ozone. In 1997, spectroscopic analysis revealed the dimeric (or diatomic molecule) absorption function of molecular oxygen, that is, this absorption function occurs when the oxygen molecule is in the concentrated phase, and the absorption function is best if the molecular oxygen is hidden in the ice.

The position of the absorption spectrum of the dimer depends more on latitude and longitude than on the albedo of the surface, which shifts upwards as latitude increases. Conversely, the absorption spectrum of ozone shifts downward as latitude increases. Laboratory simulations have shown that O₂ does not aggregate in areas above 100 K on the upper surface of Ganymede, but spreads into the ice.

When sodium was discovered on Europa, scientists began searching for it in Europa's atmosphere, but by 1997 they had found nothing. It is estimated that sodium is 13 times less abundant on Ganymede than on Europa, possibly because of the inherent lack of the substance on its surface or the magnetosphere that keeps these high-energy atoms out. Another trace component present in Europa's atmosphere is atomic hydrogen, which has been observed in space 3,000 kilometers above the surface of the moon. Its number density on the surface of the star is about 1.5 × 10⁴ cm³.

Between 1995 and 2000, Galileo Galilei flew by Ganymede six times at close range and found that the moon had a long-standing magnetic moment that was independent of Jupiter's magnetic field, estimated to be 1.3 × 10¹³T·m³, three times larger than Mercury's magnetic moment. Its magnetic dipole is at an angle of 176° to the axis of rotation of Ganymede, which means that its magnetic pole is facing Jupiter's magnetic field. The north pole of the magnetosphere is located below the orbital plane.

The dipole magnetic field created by this long-term magnetic moment is 719±2 nanotesla in the equatorial region of Ganymede, exceeding the strength of Jupiter's magnetic field here, which is 120 nanotesla. The magnetic field in the equatorial region of Ganymede is facing Jupiter's magnetic field, which makes it possible for its field lines to reconverge. The magnetic field strength of the north and south pole regions is twice that of the equatorial region, which is 1440 nanotesla.

The long-standing magnetic moment carves a space around Callisto, forming a small magnetosphere embedded in Jupiter's magnetic field. Europa is the only known moon in the solar system that has a magnetosphere. Its magnetosphere diameter is 4-5 RG (RG = 2,631.2 km). In regions below 30° latitude on Calliste, the field lines of the magnetosphere are closed, and in this region, charged particles such as electrons and ions are trapped, forming radiation belts.

The main ion contained in the magnetosphere is a single ionized oxygen atom, O+, which is consistent with the characteristics of Ganymede's oxygenated atmosphere. At latitudes above 30°, the field lines in the polar crown region spread outward, connecting the ionospheres of Ganymede and Jupiter. High-energy (up to tens or even hundreds of kilovolts) electrons and ions have been found in these regions, possibly leading to the aurora phenomenon in the Ganymede polar region. In addition, heavy ions that fall in the polar regions are sputtered, eventually darkening the ice on the surface of Ganymede.

The interaction between the magnetosphere and Jupiter's magnetic fields is similar in many ways to the interaction of the solar wind and the Earth's magnetic field. For example, the bombardment of the magnetosphere by the plasma orbiting Jupiter on Ganymede in the reverse orbital direction is very similar to the bombardment of the Earth's magnetic field by the solar wind. The main difference is the speed of the plasma flow – supersonic on Earth and subsonic on Europa. Because the plasma flow velocity is subsonic, the magnetic field on the side of Ganymede's reverse orbit does not form a bow shock wave.

In addition to its own intrinsic magnetosphere, Europa also possesses an induced-dipole magnetic field, the existence of which is related to changes in the strength of Jupiter's magnetic field near Callisto. The strength of this magnetic field is an order of magnitude weaker than that of Ganymede, which is 60 nanotesla in the magnetic equatorial region, which is only half the strength of Jupiter's field.

Europa's induced magnetic fields are very similar to those of Europa and Europa, suggesting that the moon may also possess a highly conductive subterranean ocean. Since Europa's internal structure is completely differentiated, and it has a metal core, its inherent magnetosphere may be generated in a similar way to the Earth's magnetic field: as a result of the movement of matter in the inner core. If the magnetic field is a product of the generator principle, then Europa's magnetosphere may be caused by the convective motion of its inner core.

Although Europa is known to have an iron core, its magnetosphere remains mysterious, especially as other moons of the same size do not. Some studies suggest that in Callisto's relatively small size, its core should have been cooled enough to allow for the flow of the core and the generation of magnetic fields.

One explanation claims that the orbital resonances that cause tectonic deformation of the star's surface also play a role in maintaining the magnetosphere: Calliste's orbital eccentricity and tidal heat are gained by some orbital resonances, while the mantle also acts as an insulating core to prevent it from cooling, and another theory is that the magnetosphere is caused by residual magnetism in the silicate rocks in the mantle. If the satellite had had a strong magnetic field based on the generator principle in the past, the theory would have worked.