Uos
Uos is a small icy moon orbiting the gas giant Pentas, its surface is covered by a layer of black ice very rarely punctuated by small rock formations. Its surface easily reaches 2.7 Kelvin and it has no atmosphere, none can survive there save Sailor Uos herself.
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The liquid of the vast ocean covering the entire moon is mixed with black earthen minerals which give it its black appearance, even when not frozen. The ice itself is about 5.5 kilometres deep before reaching a layer of liquid (an almost water without oxygen mixed with soil and oil) and then about 3 kilometres deeper before rock, and lastly in the centre is a rather cool magna core. Eruptions are extremely rare on the moon.
Starseed
The Uos starseed marks its holder with the symbol of Uos - a black triangle - at birth. The starseed itself holds a dark light.
Extinct
Uos cannot sustain life and cannot be terraformed, though there is evidence deep in the soil under the ice that at one time there were fish-like lifeforms and simple water plants. However now all organic matter is fossilised or decayed to oil. On the surface there are also a few frozen bodies of explorers who succumbed to the cold. Not all of them are Edionan.
History
Uos had, at one time, the capability of life to rise and evolve, but a series of volcanic eruptions slowly shredded the atmosphere of the moon. It also helped make the ice black. Over time, the volcanic activity quietened down as the water upon the moon froze.
During the first age of space exploration, all explorers of Uos never returned. This gave the moon a reputation of being the place the Edionan equivalent of Death lived. One lucky explorer came back frozen to death in his bubble with a hunk of black ice from the moon. Later advanced explorers brought real information about the moon by flying close by and passing it. They learned that it was surrounded by black sea of ice.
Edionans use the phrase "Going to Uos" to say they are going on a long journey they might not return from. Edionans with majorly contagious infectious conditions are said to be "touched by Uos". Criminals which commit extremely serious crimes and sentenced to death are said to be "Sentenced to Uos" (i.e. gen the death penalty). Those who barely escape death are "Escaping Uos' gravity well".
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In contrast, despite Meidans living much closer to Uos, they take a much less grave view of their fellow moon. While the connection with death remains it is seen as a necessary part of the life cycle, though before Cataclysm very few Meidans had actually died. Overall, they had a more respectful view of Uos.