Which planet has moons that exhibit sulfur dioxide volcanism and water ice?

The correct answer is Jupiter, primarily due to its moon Io, which is one of the most geologically active bodies in the solar system. Io is known for its extensive sulfur dioxide volcanism, resulting from intense tidal heating due to its gravitational interaction with Jupiter and other Galilean moons. This ongoing geological activity leads to the eruption of sulfur dioxide, which creates a unique and dynamic landscape on the moon.

In addition to the sulfur-dominated geology of Io, Jupiter's other moons, such as Europa, are notable for their subsurface water ice. Europa, in particular, has a smooth, icy surface that scientists believe covers an ocean of liquid water beneath, making it one of the most promising locations in the search for extraterrestrial life.

The other planetary options do not possess the same combination of features. Mars has seasonal water ice and some evidence of past volcanic activity but lacks ongoing sulfur dioxide volcanism. Neptune's moons, while interesting, do not exhibit volcanic activity of this kind. Earth does have active volcanoes, including those that release sulfur dioxide; however, it does not have moons that exhibit both sulfur dioxide volcanism and water ice in the same manner as Jupiter’s moons.