木卫四, also known as Europa, is one of the largest moons of Jupiter. It is primarily composed of water ice and is believed to have a subsurface ocean beneath its icy crust. This ocean may contain more water than all of Earth's oceans combined, making Europa a key target in the search for extraterrestrial life. The surface of Europa is characterized by a smooth, icy terrain with numerous cracks and ridges. These features suggest that the moon is geologically active, with the potential for interactions between the ocean and the surface. Scientists are particularly interested in exploring Europa to understand its potential habitability and the conditions that may support life.