The Horizon System: Rhodactis, the Ruin Author
2nd A (2)
Rhodactis (Cool Superjupiter, Planet)
System - Horizon-Actinophrys
Mass - 3,514 Earths (11.06 Jupiters)
Radius - 64,876 kilometers (10.18 Earths)
Global Average Temperature - -88.57°C
Day Length - 7h 36m 34.2s
Year Length - 64.30 years
Number of Satellites - 3644
ESI - 0.302
Etymology - From the ‘bullseye mushroom’ corallimorph Rhodactis bryoides, for its large size and dense covering of multicolored pseudotentacles.
Overview
With a mass pushing well over eleven times Jupiter’s, Rhodactis is by far the single most massive planetary body in the Horizon System. It is only outweighed by the system’s four stars and two brown dwarfs. Like most large super-Jupiters, Rhodactis is extremely dense, with a bulk density slightly less than that of gold. This allows the eleven Jupiter masses’ worth of material to compress down into a sphere actually slightly smaller than Jupiter. The churning of exotic metallic hydrogen in its core generates an immense magnetic field over 500 times stronger than Jupiter’s, but even this is overshadowed by the frankly ridiculous magnetization of brown dwarfs Physalia and Praya.
Besides its immense mass and density, Rhodactis is not all that different from Jupiter or Saturn. Immense amounts of primordial heat warm it to Jupiter-like temperatures despite being nearly as far from Actinophrys as Uranus is from the Sun, while its immense rings are formed from the ancient remains of shattered moons, just like those of Saturn. Rhodactis’s great distance from its sun allows its immense gravity to command a truly enormous region of space filled with a correspondingly enormous number of moons - with thirty-two round moons and innumerable asteroid-sized ones, the largest of which is nearly twice the mass of Earth, Rhodactis hosts one of the grandest lunar systems in the galaxy.
“We get asked fairly often why we would cooperate with people like the Horizonians when their idea of ethics and purpose is so different from ours.
I suppose the ultimate reason is that we don’t care enough about those ideological differences to kill each other over it like the Coalition does, but more proximately we can appreciate a civilization which is keenly aware of its mortality. All too often the denizens of this Galaxy forget that there are things bigger than they are, but Horizon has never done so no matter how expansive they become.
On a personal level, I just think they’re interesting to watch. It doesn’t matter to us all that much if they survive or not, but their attempts to encompass the rule of Nature are quite entertaining.“
- Emissary of the Silence ‘Jiāngshān’, Unofficial Response to “Observations on the Ideological Incompatibility of Modern Federation-States“ (2288)
Past & Future
Rhodactis formed far from its sun, collapsing from a protoplanetary disk instability. This top-down formation history is much more like that of stars than of planets, such that if Rhodactis formed alone it would probably have been classified as a sub-brown dwarf and not a planet. But there is little difference between a large planet and a small brown dwarf, and the academic classification of such an object matters little to its effects on its home system.
Rhodactis’s gravity is strong enough that it kicked out all the forming gas giants of Actinophrys, forcing Chrysaora into the extreme inner system and pushing the Resonant Worlds into the habitable zone. As it migrated towards Actinophrys, gas and dust from the protoplanetary disk piled up around the planet, forming a protolunar disk as wide as Earth’s orbit around the Sun. If allowed to mature, this disk would have probably condensed into a few Earth-sized moons, but the Horizon System supernova blew it away in a stillborn state, leaving dozens of half-formed moons. Over the next billion years, these evolved into the unusually crowded lunar system Rhodactis possesses today.
Civilization
Rhodactis is about as bright in Horizon’s sky as Saturn is in Earth’s, making a circuit through the celestial sphere once every 22 Horizonian years or so, which is coincidentally close to the pre-industrial lifespan of Horizon’s sapients. This fact led nearly all Old Horizonian cultures to ascribe the domain of death (and rebirth, when applicable) to the planet. Though historically Rhodactis’s celestial domain was usually unremarkable, reflecting its unimpressive brightness compared to the other planets and the stars of the Comatula Nebula, telescopic observations revealed that this seemingly-drab dot was in fact bedazzled with gargantuan rings and dozens of multicolored moons. This discovery remains in modern cultural memory as a complete reimagining of the afterlife that Rhodactis presides over, from a postmortem oblivion or spiritual pit stop to a distant celestial kingdom of great wealth and splendor comprising dozens of subsidiary planes with every form of paradise imaginable. Correspondingly, few Horizonians still believe in reincarnation.
The splendor of the Ruin Author is not lost on the spacefaring inhabitants of the Horizon System. Its immense gravity makes it a useful hub for transit between the Actinophryidan worlds and the domains of Ceratium and Palmaria, as well as a jumping-off point for interstellar vessels. Rhodactis’s gargantuan rings are plied by mining vessels which harvest water ice for fusion fuel and dust for rare metals, while cryogenic computer cities and in-transit refueling stations populate its smaller moons. Billions of beings pass through Rhodactis every year, some on their way to other worlds across the Comatula Nebula and many others simply to bask in the majesty of this bejeweled titan.
Myriad Celestia - The Cosmic Reef (Moons of Rhodactis)
Like most gas giants of its size, the planet Rhodactis is surrounded by an impressive entourage of satellites. Of the thousands of moons that orbit this bloated giant, some thirty-two are large enough to be considered worlds in their own right. Both their numerical abundance and their sheer variety make the moons of Rhodactis a standout case among even the other Authors, rivaled only by the biological wonderlands of Physalia or Amazonia’s Morpho. From the tidal hells of the Arenicolan Interior to the frozen, chromatic wastes of the Pristine Exterior to the strange giants of the Captive Worlds, all take on a strange kind of life even if their lands remain sterile.
A. The Arenicolan Interior
From left to right: Goniopora, Zoanthus, Favites (Irradiated Intermediary), Plerogyra, Alveopora, Cyphastrea, Cycloseris, Caulastrea
Due to their 1:1 orbital resonance, Cycloseris and Turbinaria cannot align.
At the very core of Rhodactis’s moon swarm is a set of hellishly inhospitable worlds. These eight moons are so close to their parent planet that they complete their orbits in less than a day. The vast gravity of Rhodactis flexes and squeezes them as they move through their elliptical orbits, generating huge amounts of tidal heat that powers active volcanism on all eight worlds. Many are wreathed in tenuous atmospheres of volcanic emissions and surfaces scarred by great eruptions, while on some of the smaller members of the series volcanic activity is powerful enough to blast chunks of rock and ice straight into space. All are also bathed in the radiation belts of Rhodactis’s enormous magnetosphere - their surfaces are so radioactive that even inanimate machines would be scrambled to disrepair.
I. Zoanthus
At some 700 kilometers across, Zoanthus is the largest of Rhodactis’s ring shepherds and the only one massive enough to collapse into a sphere. Though on its own such a world would have long cooled off to a frozen, dead rock, extra heat is constantly injected into Zoanthus by the tidal forces of Rhodactis, allowing this tiny moon to sustain active volcanism at 1.7 billion years of age. Rhodactis’s chromatic, sulphur-streaked surface is marred by huge cracks and twisting volcanic labyrinths, products of internal fires not its own.
IIA. Goniopora
Like a Pluto-sized version of our Solar System’s Io, Goniopora is a world of ash and lava. Its sulphur-covered surface spews hateful death as forty watts of geothermal heat explode out of every square meter of its surface, a frankly ridiculous amount compared to Io’s own ~2 watts per square meter of tidal heat. This extreme heating results in appropriately violent volcanism - plumes of sulphur gas as large as the moon itself erupt nonstop, while not-infrequent larger blasts send kilometer-sized chunks of the moon’s crust into deep space.
IIB. Alveopora
Rosy Alveopora’s strange surface is composed of aluminum minerals like sapphire, kyanite, and ugrandite garnets. Viscous, aluminum-rich lavas form great, fissured ‘continents’ capped in ethereal blue crystals of dry ice, while volcanic ash from nearby Goniopora flows down its high plateaus like rain. Vast basins collect ‘seas’ of fine dust, which forms a levitating quicksand that drifts in waves across the volcano-marred surface thanks to the shifting pull of magnetic currents.
III. Plerogyra
Though Plerogyra is about the same size and shape as our own Moon, this hellish world is nothing like silent Luna. This moon receives some 40 times as much tidal heating as Io does, raising the surface temperature by nearly 200 degrees. Predictably, Plerogyra is extremely violent, with only a thin, weak crust covering an immensely deep internal sea of magma. Volcanic explosions can send huge chunks of rock hurtling through the sky, crashing through the surface like meteors when they land, while the ebb and flow of internal heat can occasionally just melt the whole surface entirely. Few places in the universe are so harsh as this.
IVA. Turbinaria
Beyond the volcanic chaos of the inner part of the Arenicolan Interior is a hazy, lacustrine world. Turbinaria’s volcanic activity follows a pattern similar to Venus’s, where heat builds up for millions of years before the surface is entirely renewed in a titanic wave of volcanic activity. Turbinaria releases massive amounts of carbon monoxide and methane during these resurfacing events. Carbon monoxide replenishes the radiation-eroded atmosphere, while methane is processed by radiation into more complex hydrocarbons which rain out into shallow seas. Further radiation processing then slowly transforms the ocean into a tarry, tholin-rich mud. Today, Turbinaria is in the late stage of this process, with a thin atmosphere and only small remnants of its once-wide seas. It will not be long before fire returns to claim this world and start the cycle all over again.
IVB. Cycloseris
Though Cycloseris is a veritable twin to Turbinaria in terms of its physical properties, they don’t look very similar. Cycloseris undergoes the same cycle of resurfacing, ocean formation and ocean loss that Turbinaria does, but their cycles are out of sync. While Turbinaria is at the very end of its ocean-bearing phase, Cycloseris is just at the beginning, with warmer temperatures, a thicker atmosphere, and expansive seas that cover some 10% of its surface. But even at its best, Cycloseris is a dry world - vast plains of silicate rock and asphalt sand surround the ocean basins, forming cold deserts watered by rain only once every few centuries.
V. Cyphastrea
Cracked and fissured Cyphastrea is the first aquarian moon of Rhodactis, a Pluto-sized body about 10% water by mass. With a surface of dusty, blue-grey ice and a thin atmosphere of mostly oxygen, Cyphastrea almost resembles a miniature version of Jupiter’s moon Ganymede. It has a lot more in common with Io instead, though - though it is does not receive enough tidal heating to bake it dry, Cyphastrea’s icy shell is pierced through with thousands of active cryovolcanoes and erupting fissures which cast a veil of snow around this small world. Some of the largest cryovolcanic complexes are surrounded by giant rings of complex organics, which some have controversially suggested to be a sign of life underneath the crust. But with little impetus to drill through the 20 kilometer-thick crust, we will never know what lies in the salty subsurface ocean beneath.
VI. Caulastrea
At just over 1800 kilometers across, Caulastrea is one of the smaller moons of Rhodactis. With low density and consequently low gravity, it has essentially no atmosphere despite being nearly as large as Alveopora, which does have one. Despite its airlessness, Caulastrea is still an active world. Its surface is marred by huge cracks and coronae while huge effusions of water-based cryolava form huge plateaus not unlike the flood basalts of terrestrial worlds. Like our Moon, much of Caulastrea’s surface is covered in a loose, shifting regolith of fine dust, but here it is composed of snow, dry ice, and complex organic compounds rather than silicate rock.
B. The Irradiated Intermediary
From left to right: Mycedium, Trachyphyllia, Platygyra, Pectinia, Seriatopora, Favites, Blastomussa
Co-orbital relationships bar Porites, Stylophora and Pocillopora from alignments, while a resonance separates Hydnophora from its kin.
Beyond the exploding, radioactive hellscapes of the Interior are set of eleven not-quite-Titans. With the exception of airless Porites, the members of the Irradiated Intermediary are terrestrial worlds between one and two times as massive as Earth’s Moon. Though not close enough to Rhodactis to experience a tide-induced meltdown, all of them receive enough tidal heating to remain geologically active, even at their advanced age. The thick layers of water and ammonia that once lay atop their rocky mantles have been scoured off by a point-blank supernova, transformed into seas of nitrogen and oxygen.
VIIA. Mycedium
Crater-riddled Mycelium is the warmest member of the Intermediary and one of only two of its number with surface temperatures above the boiling point of nitrogen. Due to its relative proximity to Rhodactis and an unusually resistant interior, tidal heating is significant for Mycedium. The surface temperature is elevated some 80°C through geothermal activity alone, allowing the hydrogen sulphide that spews from its innumerable volcanic craters to condense into shallow seas. But geothermal activity can heat a planet only so much, so Mycedium is trapped in an eternal global snowstorm as volcanic vents vaporize its oceans and the freezing atmosphere sends them pouring right back down into their steaming seabeds.
VIIB. Pectinia
Though not too dissimilar from its co-orbital partner Mycedium, Pectinia is still a unique world. Much like our Mercury, some 70% of Pectinia’s mass is in the form of iron, not rock. The magnetic field that emanates from Pectinia’s molten interior protects its methane-rich atmosphere from being blown away by the radiation currents of Rhodactis The methane generates an extreme greenhouse that helps Pectina sustain a global sea of carbon dioxide. The constant onslaught of rain as this sea boils and freezes at the same time grinds what little land manages to rise out of the violet ocean down to gnarled spires, which rise like undead claws from in the blustery gloom.
VIII. Hydnophora
Too far away from Rhodactis for tidal heating to relieve the frigidity of the outer system, Hydnophora is the first of the Seas of Air, and by far the most volatile of its kind. Intense volcanism and ample geothermal heat try to boil Hydnophora’s oxygen oceans from the bottom up even as the gas rains in torrents from its high atmosphere, forming a churning, convulsing froth out of which great tessera ‘continents’ erupt. Rains of reactive, highly corrosive liquid oxygen carve out great channels through their lava-riddled plains just as fast as lava oozes out of the little world to replace its losses.
IXA. Stylophora
Though less than half as large and cold enough to freeze the very air, Stylophora bears an odd superficial resemblance to Horizon. Great tongues of sturdy stone weave their way in between globe-spanning seas of liquid oxygen, while dry-ice dust storms replace the spiral eruptions of Horizon’s own atmosphere and fields of giant penitentes emulate its jungles. Though Stylophora is utterly inhospitable to life as we know it, it might be the easiest place in the Horizon System to forget how far you are from home.
IXB. Pocillopora
Though its pinked-out crust seems garish when compared to the earthy tones of most terrae, Pocillopora is downright modest compared to some of the other moons of Rhodactis. Though kept geologically active by tidal heating, several giant collisions early in its life sapped energy from this small moon, leaving it with a geological cycle too sluggish to efficiently erase impact craters. Debris reservoirs among the outer moons hurl asteroids at the Intermediary, scarring Pocillopora with millions of craters of all sizes. Many of these are filled by great crater lakes as the slow grind of nitrogen rain works to erode them to nothing.
IXC. Seriatopora
Though not especially vibrant compared to the madness that follows, Seriatopora’s stained continents make for a handsome contrast to its deep blue nitrogen seas and ice-crystal clouds. Though it is not the largest of Rhodactis’s moons, Seriatopora is one of the most active. Frequent eruptions of silicate lava sublimate deposits of water and carbon dioxide ice that immediately freeze again in the -200°C temperatures, forming strange sheets and spires of glassy ice like something from a far stranger universe.
XA. Favites
The wide, shallow seas of this rusty moon are an exclusive feature of outer-system moons. Unlike most of the moons interior to its orbit, radiation levels at Favites are too low to generate large amounts of oxygen through the splitting of water, but they are high enough to rip apart the complex hydrocarbons that would otherwise form hazes in the atmosphere. Favites thus possesses a methane-rich greenhouse atmosphere that raises the surface temperature enough to boil most of its nitrogen. Though it is quite dry, its global oceans being no deeper than fifty meters, Favites is a very dynamic world - reddish, garnet-streaked continental interiors vaguely like those of distant Chrysomallon clash with quartz and water-ice beaches, while vast dry seabeds leave multicolored pits of organic-rich mud.
XB. Porites
Though it is a fair bit larger than some of the atmosphere-bearing moons of the Arenicolan Interior, Porites’s frozen surface lies under hard vacuum. Too far from Rhodactis for tidal heating to vaporize its coat of ice and with gravity too feeble to hold on to gases, this world’s surface has grown cold and silent, fissured by icy tectonics and pockmarked by a billion years of asteroid impacts. Nevertheless, tidal forces and radioactivity in its interior are more than sufficient to melt the ice, giving rise to a vast saltwater sea buried beneath some 50 kilometers of rock-hard crust.
XI. Blastomussa
Blastomussa displays most poignantly the violence of planetary formation. This ferrian moon is slightly smaller but 20% more massive than our own Moon, but possesses an abundant atmosphere and seas of nitrogen. Blastomussa’s oxygen has been locked away by the rusting of its iron-rich surface, allowing complex organics to condense in its methane-rich atmosphere. With a large core and low internal heat budget, Blastomussa’s surface is renewed only slowly - over half of it is over a billion years old, compared to the ~100 million year-old surfaces of the other Intermediary moons. While on our Moon the scars of giant impacts are left as lava-plain maria, on Blastomussa its great basins are instead filled by real seas of deep blue nitrogen.
XII. Platygyra
With its outer crust flayed off by giant impacts, one would expect Platygyra to be a dead world. But life goes on, even on a moon stripped of its hide. The deep-green olivine of Platygyra’s surface is typical of the deep mantles of other terrestrial worlds. Though this material decays quickly in an Earth-like atmosphere, Platygyra’s air consists almost entirely of inert nitrogen which allows the material to persist, forming vast plains of green sand like those found in only a few places on Earth. Tidal forces have warped this world into a twisting maze of tectonic rifts cut through by vast channels of frigid sea, wracked in the eternal storms typical of the Seas of Air.
XIII. Trachyphyllia
As the last and largest member of the Intermediary, it is somewhat appropriate that Trachyphyllia is also the weirdest of them all. While other moons like Seriatopora and Platygyra display their fair share of exotic chromaticity, this Titan-mass world is beset by an eye-searing swirl of neon colors, from violet oceans to red-green clouds to gleaming yellow sulphur vents. Its large core generates a powerful magnetic field which funnels charged particles from Rhodactis’s radiation belts to its poles, where they react violently with its surface and atmosphere to generate the colorful chemicals that so decorate its surface. Incidentally, many of the compounds generated by this process are violently explosive, so thunderstorms on Trachyphyllia can be quite exciting.
C. The Pristine Exterior
From left to right: Lobophyllia, Euphyllia, Fimbriaphyllia, Micromussa, Acanthastrea, Homophyllia
Pavona, Cynarina, and Catalaphyllia are inclined such that they cannot mutually align with each other or the remainder of the Pristine Exterior.
As we journey further and further from the violent heart of Rhodactis’s moon system, we come across a vast expanse of ancient worlds. Though not untouched by the lashes of supernovae and the radioactive bombardment of their parent planet, this constellation of nine large moons has retained the lion’s share of their primordial identity. While the worlds of the Interior never felt the touch of water and those of the Intermediary had their icy envelopes stripped off, the members of the Pristine Exterior have retained their shells of frozen water and the great supplies of volatiles they contained.
XIVA. Euphyllia
Euphyllia is the quintessential Titan analogue; a frozen world covered in oceans of hydrocarbons and shrouded in tholin hazes. Though twice as massive and much denser, they are almost identical save for Euphyllia’s somewhat larger oceans. These seas, much like those on Titan, are a roiling solution of ethane, methane, hydrogen cyanide, nitrogen, and various long-chain hydrocarbons like those in petrol. Some have speculated about life in such a mixture, but even if Euphyllia is favorable to the development of such life, it and the rest of the Horizon System are much too young for the chemical evolution of life to come to completion in a cryogenic environment where all chemistry is slowed to a crawl.
XIVB. Fimbriaphyllia
Unlike Euphyllia, with which it shares an orbit, Fimbriaphyllia is almost entirely devoid of hydrocarbons. Without methane in its atmosphere to warm its surface, Fimbriaphyllia is much colder than its co-orbital partner and instead hosts seas of nitrogen and carbon monoxide. Though tidal forces at its orbit are an order of magnitude less than those experienced by the moons of the Intermediary, Fimbriaphyllia still experiences enough heating to partially boil its oceans, which re-condense as a thick fog in its upper atmosphere.
XVA. Acanthastrea
Red, raging Acanthastrea is a Titan in caricature. The entire moon is drowned in crimson-tinged tholins which dust its surface much like hematite rust does on Mars. Though large, this moon’s tectonics are weak, allowing pounding sandstorms of carbon dust to etch its ancient mountains into the ground. Much of the once methane-rich ocean has transformed into ethane, propane, and other heavy hydrocarbons, while the rest has been lost to space to produce a dry, static-charged world beset by violent thunderstorms.
XVB. Micromussa
As with Euphyllia and Fimbriaphyllia, Acanthastrea has its own partner in the form of the clean aquarian moon Micromussa. Micromussa is an exceptionally extravagant world with a surface covered in chromatic chemicals and gleaming rings of blue ice, exceeding even the psychedelic plains of Trachyphyllia in sheer brain-melting glory. Many of the unusual chemicals that paint Micromussa’s surface originate from a vast subsurface ocean of water, ammonia, and hydrogen sulphide, while Micromussa’s nearly inert nitrogen atmosphere allows even highly reactive pigments to persist locked up in its icy regolith. Beyond its extravagant appearance, Micromussa is not really all that strange - its only truly unusual feature is the thin set of rings which circles its equator, which shine a bright cyan due to an unknown contaminant.
XVI. Homophyllia
Much like its inner neighbor Acanthastrea, Homophyllia is a red world scoured by the radiation bands of Rhodactis. Methane in the atmosphere reacts with itself and other atmospheric gases to form a diverse mix of tholins and other complex organic compounds, which then rain out of the atmosphere onto the surface. Unlike Titan, which would be the closest analogue for this type of world in our Solar System, Homophyllia’s methane oceans are extensive and mostly pure, as an unknown catalyst deep in its seas consumes radiation-manufactured tholins and liberates methane to replenish the losses. Perhaps this is some form of proto-biological system, but the frigid oceans of this blood moon have been explored too little for us to tell.
XVII. Lobophyllia
Compared to the superficially similar Trachyphyllia and Micromussa, Lobophyllia represents a more demure take on the ‘psychedelic frozen wonderland’ trope common to a few of the weirder moons of Rhodactis. Unique among all the moons of Rhodactis, its seas are composed of relatively high-purity carbon monoxide instead of nitrogen, oxygen, or hydrocarbons. This sea is highly reducing, its unusual chemistry allowing a whole array of strange chemicals to exist in solution that color it a bright green. Nonetheless, Lobophyllia’s surface geology is not very different from that of Micromussa, resulting in the same odd hues of lavender, magenta, and deep carbon black. It has rings too, but these are rather typical features composed of water ice and not the anomalous ones that circle Micromussa.
XVIII. Pavona
Though it is the smallest of the Pristine Exterior, Pavona is still twice as massive as Titan. Unlike all of the inner moons, it lies well within the bounds of Rhodactis’s magnetosphere but outside the main radiation belts. Thus, the ambient radiation levels around its orbit are far lower than even in the depths of deep space, inhibiting most of the photochemical reactions that produce smog on other hydrocarbon-rich worlds. Only Actinophrys’s UV rays get through, which slowly convert the methane oceans of Pavona to tholins, but the action of rain scrubs this material fast enough for Pavona’s atmosphere to stay clear. Thus, Pavona is quite warm, much warmer than even similar moons like Euphyllia, Homophyllia, and Montipora whose extensive smog reflects away light. Its methane oceans thus rest close to the boiling point, covering their bulk in a soupy froth of tholin slime that grades smoothly into the hazy lowland air.
XIX. Cynarina
Cynarina distinguishes itself by being the largest and most massive of any regular moon of Rhodactis. At some 7.5% Earth’s mass, Cynarina is the only regular moon of Rhodactis more massive than Mercury, while its diameter is well in excess of that of Mars. Its thick, pressurized atmosphere has created a unique environment where the two archetypes of the Pristine Exterior can clash - boiling points are raised so that nitrogen and carbon monoxide can coexist with liquid methane and noble gases. The resulting chaotic mixture forms a wine-dark ocean that covers about half of this world’s surface, while the torrential rain that pelts its icy continents leaves them encrusted with shimmering, holographic fields of crystalline ices precipitating from the raging sea.
XX. Catalaphyllia
This greenish world with its gleaming mauve rings may not be a visual twin to the other members of the Exterior, but it shares more in common with them than is apparent at a glance. Their red hazes of tholin dust have been replaced by a thick green haze of organics similar to the material that covers half of Saturn’s moon Dione, while the methane oceans are polluted by much of the same. Its gleaming rings are the remnant of an asteroid captured from the outer regions of Rhodactis’s moon system, much like those of the other ringed Exterior moons.
D. The Captive Worlds
From left to right: Montipora, Acropora, Galaxea, Leptoseris
Far beyond even the distant orbits of the Pristine Exterior is a small set of four strange worlds. Though not physically unlike their inward brethren, the Captive Worlds are united by the fact that they are foreigners who formed far afield as fellow planets of the Horizon System. Together with swarms of asteroids also shackled to Rhodactis’s immense gravity, they wander the outer reaches of the planet’s sphere of influence in yearlong orbits. As might be expected for a ragtag band of exiled former planets, they share little in common with each other.
XXI. Leptoseris
Though similar in appearance to Titan, Leptoseris is a proven aberrant. It is the single largest solid body in the entire Horizon System, beating out even giant super-Earths like Tridacna and Stephanomia despite being only 1.7 times the mass of Earth. Though this mass is more than all the other moons of Rhodactis combined, Leptoseris owes its large size to its composition - the moon is composed almost entirely of water. Its immense subsurface oceans contain tremendous amounts of dissolved gas that spews out through numerous cryovolcanic vents, dousing the thin crust in liquid methane and building up an atmosphere 50 times thicker than Earth’s. Under these conditions, the whole surface is drowned by an ‘ocean’ of supercritical nitrogen, whose hazy, ethereal currents carve channels into mountains kilometers high.
XXII. Galaxea
Inexplicable Galaxea is one of the most spectacular anomalies of the Horizon System - a temperate, Earth-like world hanging in a distant orbit around a Saturn-like giant. Though far beyond the traditional habitable zone, its surface temperatures are clement and seas of liquid water flow across its surface, even while its inner neighbors languish in frigid baths of liquid nitrogen and methane. This is made possible by an atmosphere of hydrogen thicker than Venus’s, which raises the surface temperature by nearly 200 degrees. Though the surface conditions would not be unsuitable for life, Galaxea’s seas are totally sterile. It is unclear why this is the case, but it is all the better - were life to arrive, it would quite possibly metabolize the hydrogen atmosphere and freeze the planet over, causing its own extinction.
XXIII. Acropora-Montipora
With a meandering, 10-year orbit as wide as Earth’s, the binary moon Acropora-Montipora caps off the weirdness of the Captive Worlds, along with the major moons of Rhodactis as a whole. The two Mars-sized moons orbit each other once every 14 hours or so, trapping each other in a mutually-locked configuration where each hangs unmoving in the other’s sky. They themselves are a seemingly-ordinary slice from the Exterior; Acropora a chromatic, nitrogenous world painted with volatile pigments and Montipora a haze-shrouded Titan riddled with seas of methane and ethane. Here, where Rhodactis and the other moons are but distant pinpricks and the dim light of Actinophrys only barely overpowers the shine of distant suns, it is easy to forget that you are not alone.
