The planets in our solar system can be divided into two categories: jovian planets and terrestrial planets. Jovian planets consist of those with larger masses and are also made up mostly of hydrogen and helium gas. This includes the planets of Jupiter, Saturn, Uranus, and Neptune. These planets are like Earth in that moons orbit them, but unlike Earth, there are more than 170 known moons that orbit the jovian planets. Jupiter and Saturn each have 60 moons orbiting them. The most interesting of these moons are the four Galilean moons that orbit Jupiter: Io, Europa, Ganymede, and Callisto. Io is the most volcanically active world in the solar system. Tidal heating, meaning the effect of Jupiter’s tidal forces, are what keep Io so hot inside. Europa, on the other hand, is covered with water ice. Scientists believe that a large ocean lies beneath the icy exterior. Ganymede is the largest moon in the solar system, and its surface is also made of water ice. Callisto, the outermost Galilean moon, looks like “a heavily cratered iceball” and has many impact craters. I was fascinated by learning about these moons because they are so different from the moon that orbits Earth. I wonder if anything would change in our lives on Earth if our moon had different characteristics, such as having ice water for its surface or massive volcanoes.