9. 1 the moons of the outer solar system. Several of the jovian moons, moons that orbit jovian planets, are considered prime candidates for being potentially habitable. As of early 2010, the 4 jovian planets were known to have at least 165 moons among them. One of galileo"s great discoveries was finding the four large moons of jupiter: in 1610 galileo published these findings in his pamphlet the starry messenger . These four bodies of mass he identified are known as galilean moons of. Dutch scientist christiaan huygens found the largest of saturn"s moons, Giovanni cassini discovered 4 more moons around saturn. The jovian moons come in a wide range of sizes. The smallest ones aren"t much bigger than a single mountain on earth. Some are actually very large: almost the same size as some planet and sometimes even bigger, ganymede and titan are bigger than mercury, io, europa and callisto and neptune"s moon triton are all bigger than.