Moons of the Solar System Postcards Everybody knows by name the 8 planets of the Solar System (and Pluto). But what about the 181 moons? This is a minimally illustrated postcard set made of 9 cards containing every moon and dwarf planet pictured with its planet in proportion. Ganymede is the biggest moon of the Solar system, bigger than Mercury. Phobos could fit inside Olympus Mons, the tallest known mountain of the Solar system. Back of the card, with orbits of the inner planets. All the moons of Uranus are named after characters from the works of William Shakespeare and Alexander Pope. Titan is the only natural satellite known to have a dense atmosphere, and the only object other than Earth where clear evidence of stable bodies of surface liquid has been found. Our moon is the biggest relative to its planet. The size of moons and planets inside a card are in proportion. Triton makes up more than 99% of the mass of Neptune’s moons. Back with orbits of the gas giants. There are currently 5 recognized dwarf planets, but the number could grow up to hundreds. Ceres is the only one in the asteroid belt (between Mars and Jupiter), the others are trans neptunian.