Final answer:
Tethys is one of Saturn's larger moons, characterized by an old, cratered surface that indicates past geological activity, similar to traits observed on other moons in the outer solar system like Ganymede, Callisto, and Triton.
Step-by-step explanation:
Tethys is one of Saturn's larger moons which is old, dark, cratered, and suggests past geological activity. Other Jovian moons, like Ganymede and Callisto, are composed of water ice and show similar cratering. This indicates the age of their surfaces since the number of craters correlates with how long the surface has been exposed to space debris impacts. Ganymede, in particular, is the largest moon in the solar system and its surface tells a story of geological change through its craters, with some areas being younger than others as evidenced by less dense cratering. Similarly, Saturn's moon Titan is unique because it has a thick atmosphere and features hydrocarbon lakes, and unlike Tethys, it has a complex methane cycle mimicking Earth's water cycle. Triton, around Neptune, also has an interesting geological history with features like nitrogen gas geysers.
These moons of the outer solar system give important clues about their formation and evolution through their various characteristics and processes observed, such as cratering, atmospheric composition, and signs of volcanic or tectonic activity.