Why are no impact craters visible on Io?

The correct reasoning lies in the dynamic geological activity of Io, which is known for being the most volcanically active body in the solar system. This immense internal heat, generated primarily by tidal heating from the gravitational pull of Jupiter and its other moons, causes the surface of Io to be continuously reshaped.

As a result, any impact craters that might form on Io are often destroyed or buried beneath new volcanic deposits or lava flows. This geologic activity effectively erases evidence of past impacts, leading to the absence of visible craters. In contrast, other celestial bodies with less geological activity show numerous craters because they do not undergo such constant resurfacing processes.

Tidal forces result in a transformation of the surface that happens rapidly on geological timescales, contributing to the crater removal or alteration, which is why the extreme activity on Io dictates the visibility of impact craters.