Image from Steve Bowers
Hyxuym is far from any star, and is entirely dark apart from rare volcanic eruptions
World Hyxuym
System None
Type Stevensonian cryogaian
Diameter 12756 km
Surface temp 26K
Constellation Auriga
Distance from Sol 820ly

Hyxuym is a Hider colony occupying a frozen terrestrial Stevensonian-class planetary-mass object in deep space. Most information about this world comes from Hiders who have emigrated to the Deeper Covenant polity known as The Realm, 110ly from Hyxuym. The Hider Colony on Hyxuym was established in 3877 by the Spacefarer Union craft Zhōnghuá; this craft had picked up a group of Hider refugees fleeing from a conflict in the Oort cloud of Menkalinan, and agreed to drop them off at a suitable world in deep space in return for data storage commitments. The Hider contingent, nearly 12,000 strong, agreed to preserve a quantity of important Union records in perpetuity on this isolated world.


Hyxuym was originally an Earth-like world in the habitable zone of a stellar system; this world had developed primitive life in the shallows of its seas and around deep-sea vents. Three billion years ago Hyxuym was expelled from the system after exchanging momentum with a migrating gas giant, and once the planet reached interstellar space the seas and atmosphere began to freeze. Now a deep-space Stevensonian terrestrial world, Hyxuym is covered in concentric layers of frozen nitrogen, methane, carbon dioxide and water ices. However the internal heat of this world, derived from radioactive decay, is sufficient to warm the surface to an average temperature of 26 Kelvin.

This internal heat also drives a moderate level of tectonic activity so that the icy layers on the planets surface have been disturbed and mixed by continental drift, subduction and volcanic eruptions. Remnants of the original microbial biosphere have survived near hot vents under the ice, which maintain a high-pressure liquid zone along several of the plate boundaries. A deep biosphere also exists in the warm rock, consisting of microbes which use thermal gradients to maintain a minimal metabolism. The planet also exhibits a moderate rate of volcanism, with around thirty active eruptions every standard year; these contribute to a thin atmosphere which constantly freezes out between eruptions.

The Hider group, mostly nearbaseline humans and provolved gorillas, belonged to the Kelkaj Inda (The Worthy Few), a fatalistic sect of eschatologists opposed to the rule of the Archai. They established a number of small under-ice habitats near geothermal hotspots, each habitat extracting around 1GW of power from the hot rocks, supplying enough life support including artificial food production to support (on average) around ten thousand people. By 5000 AT the population of this world exceeded one million.

The Volcano Chasers

Over time cultural drift introduced a more optimistic outlook in some sections of their society, and new factions developed; observing the steady eruption of volcanos along the various plate boundaries, one group devised technology that could exploit these events, and adopted a nomadic life on the surface of this world chasing eruptions. By surrounding the volcano with collection equipment these Volcano Chasers could extract resources and heat from the gases expelled by the eruption, including large quantities of volatiles and rock vapour from deep under the ice. These nomadic populations soon increased, exceeding the population in the deep-ice thermal habitats by an order of magnitude.

The Minimalist Faction

When the Kelkaj Inda first arrived at Hyxuym their leaders proscribed the use of fusion on this world; by reducing their energy use to geothermal sources, they hoped to remain hidden even if their planet came under observation. But during the ComEmp era a number of Volcano Chasers became frustrated with their nomadic lifestyle, and started to build fusion power plants to support their power requirements between eruptions. By 6000 AT the use of Hotpoint fusion generation plants allowed the population of Hyxuym to exceed 70 million. Waste heat from the habitats vapourised local deposits of volatile ice and the planet developed a permanent thin atmosphere (mostly nitrogen with CO2 and methane traces). Some of the most devout Kelkaj Inda objected to this development, saying it drew attention to their presence.

Another concern was the fate of the indigenous biosphere, which was rapidly being displaced by Terragen microbes in most locations as the environment became richer in oxidising chemicals. Certain environmentalist factions among the Hiders protested against this development, and advocated a return to a minimalist lifestyle. Vastly outnumbered, the Minimalist faction nevertheless caused considerable disruption with a program of terrorist outrages, leading to an authoritarian crackdown in most of the habitats on Hyxuym.

The Current Era

Image from Steve Bowers
Alleyn is the largest city on Hyxuym, a domed habitat deep under the ice, mostly lit by the purple growlights in the vertical farms that grow much of their food.
Far from any space routes this cold planet is rarely visited, except by Spacefarer Union craft periodically depositing more data for long-term storage. Each visit by an outside craft carries away a few refugees from the sporadic conflicts and authoritarian regimes; many end up in the Realm, where the Deeper Covenant continues to monitor developments on this secretive world.

Some former inhabitants of Hyxuym have become active in the search for deep space life, and in efforts to preserve such life where it has already been discovered. Stevensonian planets are numerous, but difficult to find, and life-bearing examples even more so; many former Hyxyumites have become specialists in this branch of xenobiology.
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Development Notes
Text by Steve Bowers
Initially published on 25 January 2016.