The seventh inner moon of Neptune

Area of Science:

• Planetary Science
• Astronomy
• Neptune System Dynamics

Background:

• Voyager 2 imaged six inner moons of Neptune in 1989, interior to Triton.
• These moons, along with Neptune's rings, are likely younger than Neptune and have undergone fragmentation from cometary impacts.
• The inner moons are thought to have formed after Triton's capture.

Purpose of the Study:

• To report Hubble Space Telescope observations of Neptune's seventh inner moon, Hippocamp.
• To provide updated astrometry, orbit determinations, and size estimates for all inner moons.
• To investigate the origin of Hippocamp and its relationship with Proteus.

Main Methods:

• Utilized Hubble Space Telescope observations to image Neptune's inner moons.
• Employed an image analysis technique involving distorting consecutive images to compensate for orbital motion.
• Performed astrometric measurements and orbit determinations for Naiad, Hippocamp, and other inner moons.

Main Results:

• Confirmed the existence of Hippocamp, a small moon with a mean radius of approximately 17 kilometers.
• Observed Naiad, Neptune's innermost moon, which had not been seen since 1989.
• Determined that Hippocamp orbits close to Proteus, with a 10% difference in semimajor axes, suggesting Hippocamp is a fragment of Proteus.

Conclusions:

• Hippocamp is likely an ancient fragment of Proteus, supporting the impact hypothesis for the inner Neptune system's evolution.
• The analysis technique used is potentially applicable to discovering other moons and exoplanets.
• The inner Neptune system has been significantly shaped by numerous impacts over time.