Photos like this always make me think about how unimportant size is in determining whether one of the worlds of the solar system is an exciting place. We have Jupiter, the largest of the planets and the undisputed gravitational ruler of everything in the solar system that is not the Sun. And we have Europa, the smallest of Jupiter's four main moons, much smaller than Earth, smaller even than our own Moon. Europa's smaller than many of Jupiter's storms. But even from this distance, even though it's a relatively minor participant in this photographic composition, you can see the cracked and criscrossed surface of smooth ice that makes it a fascinating world unto itself.