THE SATELLITES
Of the 49 or so satellites all but four belong to the Jovian planets. It seems likely that more will be discovered in the future; and in fact many more may eventually be found since Jupiter and Saturn could gravitationally bind a lot of small bodies. Very small and faint satellites of the Jovian planets cou Id easily escape detection by our present technology. Two of Jupiter's satellites, Ganymede and Callisto, and one of Saturn's satellites, Titan, are as large as, or larger than, Mercu ry.
Those satellites that are reasonably near their parent planet move in nearly circular orbits in the plane of their planet's equator and in the same direction as their planet rotates. The outer satellites usually have more eccentric orbits, which are more highly inclined to the equatorial plane of their planet. The four outer satellites of Jupiter, the most distant satellite of Saturn, and the inner satellite of Neptune have orbits that are reversed from the direction of their planet's rotation. It is possible that the reason for these differences is that the outer satellites were captured by the primaries after the planets and their inner satellite systems were formed.
