Hippocamp.space
Menu

Inner moon of Neptune · Inner Neptunian system, just inside Proteus

Hippocamp

Neptune XIV · S/2004 N 1

A 35-km moon hiding in old Hubble images — possibly a chip knocked off Proteus by a comet.

Key factsExplore in 3DTelescope picker
Hippocamp at a glance
Object typeSmall inner moon of Neptune[1]
Discovered1 July 2013 by Mark Showalter, in Hubble images from 2004–2009[1]
NamedFebruary 2019, after the mythical sea-horse[1]
Diameter≈ 35 km[1]
Orbital period≈ 23 hours[1]
Mean distance≈ 105,300 km from Neptune[3]
NeighbourOrbits about 12,000 km inside Proteus[1]

Explore Hippocamp in 3D

See where Hippocamp is among the moons of Neptune on an interactive 3D map built from JPL orbital data. Drag to rotate, scroll or pinch to zoom.

Open the 3D map →
Science1 research paper in plain English, grouped by topic.Read the research →FactbookHippocamp at a glance: every number sourced or labeled.Open the factbook →Business3 ways to make money, each with an editable calculator.Run the numbers →

Found in the archive

Mark Showalter of the SETI Institute found Hippocamp on 1 July 2013 in archival Hubble images of Neptune.[1] It was too dim for Voyager 2 to detect during its 1989 flyby.[1]

Too close to Proteus

Hippocamp orbits only about 12,000 km inside Proteus, Neptune’s largest inner moon. Normally a big moon would sweep aside or swallow a small neighbour.[1][2]

A chip off Proteus?

Showalter’s team proposed that Hippocamp formed from debris knocked off Proteus by the comet impact that made Proteus’s giant crater Pharos.[1] Proteus is about 400 km across.[4]

Panning for moons

Showalter digitally warped and stacked short Hubble exposures to follow orbital motion, then extended his search beyond the rings and spotted a faint white dot.[1]

Telescope picker

Thinking about a first telescope? Answer five quick questions and we’ll suggest telescope types that fit your sky, storage space and budget — with links to browse current models.

Start the picker →

Orbit

Hippocamp circles Neptune in about 23 hours at about 105,300 km.[1][3]

Neptune Proteus (117.7 thousand km)Triton (354.8 thousand km) farthest ≈ 105.4 thousand km closest ≈ 105.2 thousand km
Top-down orbit of Hippocamp to scale, computed from JPL orbital elements (a ≈ 105.3 thousand km, e ≈ 0.001).[3] Proteus and Triton orbits shown for comparison.[3] Mean orbital elements; Hippocamp’s orbit is nearly circular and close to Neptune’s equator.

The sea-horse

It is named after the hippocampus, a mythical creature with a horse’s upper body and a fish’s tail, symbol of Poseidon and Neptune.[1]

Read more

The moon anyone could have found

How public Hubble images revealed Hippocamp.

Read →

Born from a crater?

Hippocamp, Proteus and the Pharos impact.

Read →

Neptune’s 16 moons

Where Hippocamp fits in a lopsided system.

Read →

Sources

  1. Hippocamp (moon) — Wikipedia
  2. Hippocamp — NASA Science
  3. Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
  4. Proteus (moon) — Wikipedia
  5. Mark R. Showalter — Wikipedia
  6. Hubble Space Telescope — Wikipedia
  7. Neptune — Wikipedia

Figures are rounded; where sources differ we note it. Spotted an error? Tell us.