Io is the first large moon of Jupiter and is the most geologically active body in the solar system. Its close proximity to Jupiter and tidal forces from the giant and its 3 other giant moons push and pull the moon apart internally. This causes Io to turn itself inside out and fuels its many active volcanos. Due to this constant volcanic activity the surface of Io is quite young, continually being reshaped with not a crater to be found.
Image Note: The image itself is largely original and complete. I added the "dark side" details and completed disk. The the two plumes showing at the edges of the dark side of the disk are also additions. The plumes are taken from other real images and they do appear in true scale, however some brightening of these plumes were likely applied to these original images to show detail, so I darkend them a bit and reduced the color saturation that usually results from these manipulations.