Europa is the sixth moon of the planet Jupiter. Europa was discovered in 1610 by Galileo Galilei (and possibly independently by Simon Marius), and named after a mythical Phoenician noblewoman, Europa, who was courted by Zeus and became the queen of Crete. It is the smallest of the four Galilean moons.
At just over 1,900 miles in diameter, Europa is slightly smaller than Earth’s Moon and is the sixth-largest moon in the Solar System. Though by a wide margin the least massive of the Galilean satellites, its mass nonetheless significantly exceeds the combined mass of all moons in the Solar System smaller than itself. It is primarily made of silicate rock and likely has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This young surface is striated by cracks and streaks, while craters are relatively infrequent. A water ocean exists beneath the ice, supporting various indigenous and imported algaes and other plants (terraforming began about 50 years ago)