The moon anyone could have found

How public Hubble images revealed Hippocamp.

Published 2026-10-23

Hippocamp was discovered in images that had been public for years.^[1] Its discoverer, Mark Showalter, is a senior research scientist at the SETI Institute who has discovered six moons and three planetary rings.^[5]

The search

Showalter was studying Neptune’s ring arcs in 2009 Hubble images, using a panning-like technique to stack exposures.^[1]

On a whim

He extended the analysis beyond the rings and found a faint but unambiguous white dot.^[1]

Confirmation

He checked over 150 archival Hubble images back to 2004, finding the moon at ten observation times.^[1][2]

Public data

The Hubble Space Telescope, launched into low Earth orbit in 1990, carries a 2.4 m mirror.^[6]

Because the images were public, the discovery could have been made by anyone.^[1]

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