Astronomers using the NASA/ESA Hubble Space Telescope, along with older data from the Voyager 2 probe, have revealed more about the origin of Neptune’s smallest moon. The moon, which was discovered in 2013 and has now received the official name Hippocamp, is believed to be a fragment of its larger neighbour Proteus.
A team of astronomers, led by Mark Showalter of the SETI Institute, have used the NASA/ESA Hubble Space Telescope to study the origin of the smallest known moon orbiting the planet Neptune, discovered in 2013.
“The first thing we realised was that you wouldn’t expect to find such a tiny moon right next to Neptune’s biggest inner moon,” said Mark Showalter. The tiny moon, with an estimated diameter of only about 34 km, was named Hippocamp and is likely to be a fragment from Proteus, Neptune’s second-largest moon and the outermost of the inner moons. Hippocamp, formerly known as S/2004 N 1, is named after the sea creatures of the same name from Greek and Roman mythology [1].
The orbits of Proteus and its tiny neighbour are incredibly close, at only 12 000 km apart. Ordinarily, if two satellites of such different sizes coexisted in such close proximity, either the larger would have kicked the smaller out of orbit or the smaller would crash into the larger one.
Instead, it appears that billions of years ago a comet collision chipped off a chunk of Proteus. Images from the Voyager 2 probe from 1989 show a large impact crater on Proteus, almost large enough to have shattered the moon. “In 1989, we thought the crater was the end of the story,” said Showalter. “With Hubble, now we know that a little piece of Proteus got left behind and we see it today as Hippocamp.” ...
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk. — Garrison Keillor
I can add colors to the chameleon,
Change shapes with Proteus for advantages,
- Henry VI, Part Three, Act III, Scene ii
https://en.wikipedia.org/wiki/Hippocamp_%28moon%29 wrote:
<<Hippocamp may have formed out of debris from a nearby larger moon of Neptune, Proteus. The debris was possibly ejected by the comet impact that formed its largest crater Pharos; this ejecta would have had ~50 times greater volume than Hippocamp. Hippocamp orbits relatively close to Proteus; their semi-major axes differ by about 12,000 kilometres. Hippocamp probably formed a few thousand km from Proteus; Proteus would then have gradually receded from it due to its stronger tidal interaction with Neptune. Hippocamp completes one revolution around Neptune every 22 hours and 28.1 minutes, implying a semi-major axis of 105,283 kilometres, just over a quarter that of Earth's Moon, and roughly twice the average radius of Neptune's rings. Both its inclination and eccentricity are close to zero. It orbits between Larissa and Proteus, making it the second outermost of Neptune's regular satellites. Its small size at this location runs counter to a trend among the other regular Neptunian satellites of increasing diameter with increasing distance from the primary.
The periods of Larissa and Hippocamp are within about one percent of a 3:5 orbital resonance, while Hippocamp and Proteus are within 0.1% of a 5:6 resonance. Larissa and Proteus are thought to have passed through a 1:2 mean-motion resonance a few hundred million years ago. Proteus and Hippocamp have drifted away from Larissa since then because the former two are outside Neptune-synchronous orbit (Neptune's rotational period is 16 h 6 min 36 s) and are thus being tidally accelerated, while Larissa is within and is being tidally decelerated.
Proteus is the second-largest Neptunian moon, and Neptune's largest inner satellite. Discovered by Voyager 2 spacecraft in 1989, it is named after Proteus, the shape-changing sea god of Greek mythology. Proteus orbits Neptune in a nearly equatorial orbit at the distance of about 4.75 equatorial radii of the planet. Despite being a predominantly icy body more than 400 km in diameter, Proteus's shape deviates significantly from an ellipsoid. It is shaped more like an irregular polyhedron with several slightly concave facets and relief as high as 20 km. Proteus's largest crater is Pharos, which is more than 230 km in diameter.>>
Moons around moons around planets around stars around galaxies around universes Just finishing Anathem in which its plot (not to spoil it) also revolves around the premise.
https://en.wikipedia.org/wiki/Hippocampus_(mythology) wrote:
<<The hippocampus or hippocamp, also hippokampoi (Greek: ἱππόκαμπος, from ἵππος, "horse" and κάμπος, "sea monster"), often called a sea-horse in English, is a mythological creature shared by Phoenician, Etruscan, and Greek mythology, though its name has a Greek origin. The hippocampus has typically been depicted as having the upper body of a horse with the lower body of a fish. In the Iliad, Homer describes Poseidon, god of horses, earthquakes, and the sea, drawn by brazen-hoofed horses over the sea's surface, and Apollonius of Rhodes, describes the horse of Poseidon emerging from the sea and galloping across the Libyan sands. This compares to the specifically "two-hoofed" hippocampi of Gaius Valerius Flaccus in his Argonautica: "Orion when grasping his father’s reins heaves the sea with the snorting of his two-hooved horses.">>
Just finishing 
