Neptune's Inner Moons and Their Diameters
This diagram shows the orbital positions of Neptune's inner moons, which range in size from 20 to 260 miles across. The outer moon Triton was captured from the Kuiper belt many billions of years ago. This would have torn up Neptune's original satellite system. Triton settled into a circular orbit and the debris from shattered moons re-coalesced into a second generation of inner satellites seen today. However, comet bombardment continued to tear things up, leading to the birth of Hippocamp, which is a broken-off piece of Proteus. Therefore, it is a third-generation satellite. Not shown is Neptune's outermost known satellite, Nereid, which is in a highly eccentric orbit, and may be a survivor from the era of that Triton capture.