Sysmounth

Sysmounth is a fictional natural satellite commonly referenced in speculative astronomy and science fiction. In the in-universe catalog, it orbits the gas giant Thalassa in the Veridia star system and is used as a representative example of mid-sized icy moons.

The name derives from a portmanteau of sys ("system") and mounth, reflecting its status as a moon of a planetary system. It was first described in the mission logs of the survey vessel Lumen-3, published in 2141 in the Veridia System Atlas.

Sysmounth orbits Thalassa at an average distance of about 1.8 million kilometers, with a near-circular orbit (eccentricity ~0.02) and a period of about 20 days. Its orbit is inclined less than one degree to the planet's equator. The moon's mean radius is about 360 kilometers, mass around 1.3×10^20 kilograms, and bulk density near 1.9 g/cm3, consistent with an icy-rock composition. Albedo is around 0.12.

Its surface is heavily cratered, with ridge networks and smooth plains formed by ancient cryovolcanic activity. Some in-universe data suggest a subsurface ocean beneath an ice crust, inferred from magnetic signatures described in fiction.

Sysmounth has appeared in multiple works of fiction, including novels and video games, as a setting for exploration and resource prospecting. There are no real-world missions or observations of Sysmounth.

See also: List of fictional moons; Veridia system.