from the end of the 19th century, dozens of much smaller jovian moons have been discovered. all these are less than in diameter, with most barely exceeding . their orbital shapes range from nearly perfectly circular to highly eccentric and inclined. many revolve in the direction "opposite to jupiter's spin" (retrograde motion). orbital periods range from seven hours (taking less time than jupiter does to spin around its axis), to some three thousand times more (almost three earth years).