Why are numerous impact craters found on Ganymede and Callisto but not on Io or Europa?

Moons within our Solar System exhibit a fascinating array of geological activities, which play a vital role in shaping their appearance. Geological activity refers to the various processes that change the landscape of a planetary body over time. This includes mechanisms such as volcanism, tectonics, erosion, and impact cratering. For instance, some moons like Ganymede and Callisto have relatively ancient surfaces with numerous impact craters, showcasing a lack of recent geological activity.
In contrast, other moons experience dynamic changes to their landscapes due to more active internal or external geological forces. Io and Europa, for example, are teeming with activity that continuously modifies their surfaces. The geological activity level of a moon is influenced by factors such as its composition, internal heat, and its proximity to other celestial bodies, which may exert gravitational forces causing tidal heating and subsequent geological change.

Io, one of Jupiter's largest moons, is distinguished by its extreme volcanic activity, making it the most volcanically active body in the Solar System. Volcanism is the eruption of material, such as lava, ash, and gases, from beneath a moon's surface. On Io, this activity is so intense that it completely reshapes the moon's surface relatively quickly in geological terms.
Due to this continuous volcanic resurfacing, impact craters are covered by newer lava flows before they can accumulate. The energy for Io's vigorous volcanic activity originates from the intense tidal forces exerted by Jupiter's gravity, as the moon is squeezed and stretched while it orbits the planet. This generates a substantial amount of heat within Io's interior, fueling its numerous volcanoes and resulting in spectacular plumes and lava flows.

Europa, another one of Jupiter's moons, experiences significant tidal forces due to the immense gravitational pull from its parent planet. Tidal forces are the result of the varying gravitational effects that different parts of a celestial body experience when another massive object, like Jupiter, is nearby. On Europa, these forces are strong enough to generate heat through internal friction, warming its subsurface ocean and keeping the ice crust in motion.
This constant movement and cycling of ice disrupt the surface, which leads to the covering or closing of any impact craters that may have been formed. The activity on Europa is strong evidence that even in the absence of traditional volcanic activity seen on Io, tidal movements alone can contribute significantly to surface changes and geological processes.

Jupiter's gravitational effects are profound, extending far beyond the planet itself and influencing its moons, particularly those in close orbit. The massive size of Jupiter means that it has an immense gravitational pull, which affects the geological processes on its moons.
Tidal forces are a direct outcome of Jupiter's gravity, leading to internal heating and geological activity on Io and Europa. These tidal forces result in various degrees of heating and internal friction, which can cause stretching, compressing, and distortion of moon surfaces. For the moons that are farther away, like Ganymede and Callisto, the gravitational effects are less intense, resulting in weaker tidal forces and, subsequently, less geological activity. Essentially, Jupiter's powerful gravitational field is a driving factor behind the stark differences in the geological landscapes among its moons, dictating the frequency of phenomena such as volcanism, tectonic movement, and surface renewal.