The Horizon System: Antipathes-Cerianthus, the Azure Duality
Lamarck
Antipathes (Cold Neptune, Planet)
System - Horizon-Actinophrys
Mass - 13.06 Earths (0.762 Neptunes)
Radius - 27,194 kilometers (4.256 Earths)
Global Average Temperature - -107.2°C
Day Length - 29h 18m 28.3s (Mutual lock)
Year Length - 6.773 years
Number of Satellites - 1
ESI - 0.370
Etymology - From the black coral Antipathes dendrochristos, for its cold, lightless habitat and low metabolism.
Cerianthus (Cold Subneptune, Planet)
System - Horizon-Actinophrys
Mass - 8.406 Earths (0.490 Neptunes)
Radius - 15,448 kilometers (2.422 Earths)
Global Average Temperature - -105.2°C
Day Length - 29h 18m 28.3s (Mutual lock)
Year Length - 6.773 years
Number of Satellites - 1
ESI - 0.508
Etymology - From the tube anemone Cerianthus membranaceus, for its active nature and because tube anemones were once thought to be closely related to the antipatharian black corals.
Overview
The last of the Resonant Worlds are a trio of glacial wastelands. A binary of deep azure Neptunian worlds circled by a frozen, Mars-sized moon, Antipathes, Cerianthus, and Relicanthus are a remnant vision of the past of all the Resonant Worlds. All three are largely composed of water; deep clouds of snow allow Rayleigh scattering to generate Antipathes and Cerianthus’s abyss-blue shades, while water ice forms the base of Relicanthus’s blue-grey shell.
Though superficially Antipathes and Cerianthus appear very similar, they are very different in their internal structure. Antipathes is a normal low-density Neptune with a hydrogen-rich atmosphere, but Cerianthus is instead intermediate in density between rocky and icy worlds, with a large, rocky core containing some 60% of its mass. Its atmosphere does not contain large amounts of hydrogen, but rather oxygen and nitrogen gases. In essence, it is really just a somewhat smaller version of Tridacna buried beneath deep layers of ice. It might even be possible that Cerianthus has a liquid ocean somewhere beneath the endless clouds of ice, though if that is the case said ocean will be under pressures and temperatures far from those we are familiar with on Earth.
“We do not choose to brand ourselves with the scars of past failures because We lack confidence in our success, nor are We attempting to project an image of false weakness. We are well aware of Our current strength.
We choose to remember Our disgraceful history because of Our progress, not in spite of it. Were We to simply forget the billions who were sacrificed to effectuate Our current state, We would be no better than the rest of those rapacious conquerors We rail against.
Our continued existence is a courtesy, not a right. You would do well to remember that.“
- The Sixth Archon, “Glittering Roads Over Heaven“, “Reasoning for the Continued Depopulation of the Halichoeres Void” (2274)
Past & Future
Like all the other binaries in the Horizon System, Antipathes and Cerianthus came together in a giant collision. While proto-Antipathes was probably not all that different from the planet we see today, proto-Cerianthus was likely significantly different. Cerianthus would have begun life with as much as 20% more mass than it does today in the form of hydrogen gas, which was stripped by the supernova which rocked the Horizon System. When the planets first collided, the debris excavated from their mantles likely condensed into a circumbinary ring that then formed Relicanthus, explaining its extremely water-rich composition.
Civilization
Antipathes and Cerianthus are theoretically possible to distinguish in ideal viewing conditions, but their brightness and the similarity in color between them make this difficult in practice. Even Relicanthus is difficult to separate visually, since its much smaller size means a much dimmer glow that is easily masked by the glare of its host planets. As such, Antipathes is afforded a secondary role in Horizonian spiritual beliefs, though it is often associated through dualist notions with Chironex, which is on the other side of the celestial sphere near Actinophrys but appears very similar in color and brightness. Though they were the subject of some pluralist beliefs during the planetary romance era of Old Horizon, interest in them declined once scientists properly understood their gaseous nature. Today, the Horizonian natives’ view of Antipathes is not all that different from the one their ancestors held 1.5 million years ago.
The spacefaring inhabitants of the Horizon System largely share its natives’ disinterest in Antipathes and Cerianthus. Not only do they have a slow orbit and conditions unfavorable to life as we know it, the mutual gravity of the binary planet and large moon Relicanthus make it nearly impossible to put anything in a stable orbit around them. Lacking trojan asteroids due to the gravitational perturbations of Cryogenia and Rhodactis, Antipathes and Cerianthus are at best a pit stop on the way to more glamorous vistas.
