Psamathe (moon)

Psamathe (), also known as Neptune X and previously as S/2003 N 1, is an irregular moon of Neptune. It was discovered by Scott Sheppard, David Jewitt, and Jan Kleyna at Mauna Kea Observatory on 29 August 2003. Named after one of the Nereids from Greek mythology, Psamathe follows a distant, highly eccentric, and highly inclined orbit with an average orbital period of about 25 Earth years. Like the majority of irregular moons, Psamathe's orbit is retrograde, meaning it revolves around Neptune in the opposite direction to the planet's orbit around the Sun.

Psamathe is estimated to have a diameter between 36 and 40 km (22 and 25 mi), though most of its physical properties are unknown. Psamathe shares similar orbital characteristics with Neptune's two outermost moons, Neso and S/2021 N 1, which suggests they originated from the collisional breakup of a once-larger moon of Neptune billions of years ago.

Discovery

Psamathe was discovered by astronomers Scott Sheppard, David Jewitt, and Jan Kleyna on 29 August 2003. At the time, the team was searching for distant moons of Neptune, using the 8.2-meter (27 ft) Subaru Telescope at Mauna Kea Observatory, Hawaii. Their search strategy involved using the telescope's camera to photograph patches of the sky around Neptune at roughly 33-minute intervals, which revealed the planet's moons as faint, slowly-moving points of light. The team detected Psamathe in images taken on 29 and 30 August 2003, and reported their discovery to the Minor Planet Center (MPC) on 1 September.