via Ed Zeltmann via Captain Neo via Pinside
Io is the innermost of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon, has the highest density of all the moons, and has the least amount of water of any known astronomical object in the Solar System.
Thank you, Wikipedia.
Fun With Bonus is the home of the semi-coherent, misguided ramblings of professional and amateur pinball players.