Born from a crater?

Hippocamp, Proteus and the Pharos impact.

Published 2026-10-23

Hippocamp’s orbit sits just 12,000 km inside Proteus’s, and their semi-major axes differ by only ten percent.^[1]

The Pharos crater

Proteus bears a crater named Pharos about 250 km across — more than half its own diameter.^[1]

The idea

Showalter and colleagues proposed Hippocamp formed from debris ejected by that impact.^[1]

Third generation

That would make it a “third-generation” moon: Neptune’s original moons were disrupted by Triton’s capture, re-formed, and then broken again by comets.^[1]

Smashed nine times

Hippocamp itself may have been disrupted about nine times in 4 billion years.^[1]

Numbered citations link to the sources list on the Hippocamp overview page.