An Etymological Dictionary of Astronomy and Astrophysics

The smallest known moon orbiting the planet → Neptune, discovered in 2013. Hippocamp has an estimated diameter of only about 34 km and orbits close to → Proteus, the outer and the second largest of Neptune’s moons. The orbital → semi-major axes of the two moons differ by only 10%. Hippocamp is probably an ancient fragment of Proteus.
Billions of years ago a comet collision would have chipped off a chunk of Proteus. Images from the Voyager 2 space probe from 1989 show a large → impact crater on Proteus, whose size compares with Hippocamp’s (Showalter et al., 2019, Nature 566, 350).

See also: Formerly known as S/2004 N 1, Hippocamp is named after the sea creatures in Greek and Roman mythology. The mythological Hippocampus possesses the upper body of a horse and the lower body of a fish. The Roman god Neptune would drive a sea-chariot pulled by Hippocampi.