He argued that all big spherical moons, including the Moon, should likewise be considered planets. It starts by describing atoms, stars, planets and their moons. The diagram illustrates the orbits of those irregular moons discovered so far. Callisto is the outermost of the four Galilean moons of Jupiter. Four of the five moons of Pluto rotate chaotically. The major moons of Uranus are airless bodies. Uranus's Desdemona may even collide with one of its neighboring moons. They have even been seen on Titan, one of Saturn's moons. The Artemis Project designed a plan to colonize Europa, one of Jupiter's moons. The collision released material that consolidated into the moons around Pluto. These were nicknamed "Earth's hidden moons". The origin of the Martian moons is still controversial. Saturn has 82 known moons, 53 of which have formal names. The point of conjunctions librates around the midpoint between the nodes of the two moons. An example of this is missions to Mars' moons, or flyby missions.