Final answer:
Europa and Enceladus have relatively few impact craters on their surfaces, indicating they're geologically active due to recent resurfacing from internal energy sources, possibly linked to tidal heating from their massive neighboring planets, Jupiter and Saturn.
Step-by-step explanation:
The relatively uncrated surfaces of Europa and Enceladus suggest recent geological activity because a heavy presence of craters would indicate an old, inactive surface constantly subjected to impacts over a long period. Instead, these moons show signs of recent surface renewals, likely due to internal forces. For Europa, observations from NASA's Galileo Mission describe a surface with few craters, colored ridges, and cracks. This 'geologically young' appearance, coupled with implications of a subsurface ocean beneath its icy crust, suggests active internal processes, such as tidal heating. The heat generated by this activity could lead to a liquid water ocean under the ice, driving geological changes and resurfacing.
Saturn's moon Enceladus also shows similar signs of activity, potentially due to Saturn's analogous tidal forces. In both cases, the moons' proximity to their respective planets results in gravitational interactions strong enough to create internal friction and heating, leading to activity that refreshes the surface and prevents the accumulation of many impact craters.
Europa's internal heat could come from the primordial heat of formation or the decay of radioactive elements, compounded by the tidal interactions with Jupiter. Enceladus is suspected to experience similar effects due to Saturn's gravitational influence. The lack of craters and the evidence for subsurface oceans make these moons of particular interest for astrobiology and the quest to find extraterrestrial life.