The Horizon System: Physalia, the Miracle Author
“And in the depths of the azure abyss
Beyond time, beyond life, beyond order imposed
Where forest and sky are sea alike
A forgotten universe, a place removed
A thousand isles, a million worlds.“
- Vassal Seleucidis, excerpt from “Invitation to the Great Beyond“
Physalia (Temperate Megajupiter, Brown Dwarf)
System - Horizon-Ceratium
Mass - 6,844 Earths (21.53 Jupiters)
Radius - 69,570 kilometers (10.92 Earths)
Global Average Temperature - 20.31°C
Day Length - 2h 35m 23.0s
Year Length - ~2.632 years
Number of Satellites - 20
ESI - 0.295
Etymology - From Physalia physalis, the Portuguese Man of War, for its integrated colonial habit and extremely painful sting.
Overview
As a low-mass brown dwarf, Physalia straddles the gap between planet and star. As is typical for brown dwarfs, it has an extremely high density, packing 21 Jupiters’ worth of mass into a sphere about the same size. This makes Physalia denser than all the terrestrial planets of the Horizon System and in fact denser than all the known elements with one possible exception. Basically the entire volume of Physalia is composed of an extremely high-pressure metallic phase of hydrogen, currents of which generate a magnetic field some 2000 times stronger than Jupiter’s, enough to near-instantly cook lifeforms and electronics alike within around a million kilometers. Though once Physalia would have been capable of performing nuclear fusion, converting deuterium into helium-3, it has long since exhausted its supplies of nuclear fuel.
Physalia’s surface conditions are not too different from those of ‘normal’ habitable-zone gas giants, with a global covering of white water clouds. However, the churning atmosphere and rapid rotation cause massive storm systems that can open the layers of water clouds to reveal deeper layers. Clouds of rock and iron in the deep interior can be exposed by particularly violent events, manifesting as weakly glowing spots on Physalia’s night side. These ever-shifting clouds along with radiant aurorae generated by Physalia’s powerful magnetosphere make eclipses on the inner Physalian Worlds a truly magical time, as the giant’s dark disk is pierced by the flickering lights of auroral columns and hurried storms.
Past & Future
Physalia orbits its binary hosts in the brown-dwarf desert, a region of space around a star where brown dwarfs are unlikely to form. This, combined with its retrograde orbit, suggest that Physalia has undergone enormous migration over the course of its life. Physalia probably first formed far beyond the frost line at a distance similar to that between Neptune and the Sun, along with several Jupiter-mass planets interior to its orbit. Perturbations induced by the nearby star Palmaria would have stretched out Physalia’s wide orbit, leading to a catastrophic interaction with the other nascent planets in its system. Most would have been ejected (one finding a new home around Actinophrys) while others would have collided with Physalia, building its enormous mass.
Unlike larger brown dwarfs, nuclear fusion contributes little to Physalia’s evolutionary history. Its fuel supplies would have been consumed within the first 50 million years of its life, leaving it glowing at a surface temperature of some 1500°C. At that time, it would have provided a small amount of heat to its satellites, enough to keep the Agalmatid Series in a runaway greenhouse state for some 500 million years.
The habitable Physalian Worlds were seeded with life only once or twice. The small planet Dendrogramma was colonized by a small contingent of Horizonian microbial lineages around 1.1 billion years ago, which then colonized all the other habitable Physalian Worlds as asteroids carried them from planet to planet. The next time anything made it to Physalia alive was during Horizon’s end-Caeliferan Mass Extinction 300 million years ago, which dumped a basically random assortment of extremophiles on Athorybia and Dendrogramma who then made their way to most of the Physalian worlds, save a few members who would later go on to develop their own unique forms of complex life.
Civilization
Physalia and all of its satellites are far too dim to be visible in Horizon’s skies, even if the glare of their host stars did not overpower their faint luminosity. Only the largest telescopes can pick them out, so they were only discovered in the very last stages of the planetary romance literary era, just before advances in rocketry allowed the Horizonians to explore their home system close up. With an angular diameter only slightly greater than Pluto’s, Physalia’s features were entirely invisible to early astronomers. The only things they knew about it were its orbital parameters, its atmospheric composition, and its approximate mass based on the orbital speed of its moons.
It was not until over a century later that the first probes were sent to explore Physalia. Those first images revealed a world far stranger and more wonderful than anyone could have predicted. From steaming jungles to antediluvian swamps to endlessly marching forests, one that exceeded even the wildest speculations of the romantic writers, save one: for all the beauty and horror that is Physalia, only the simple minds of animals call these worlds home. While modern Horizonians’ spacefaring ancestors may have once travelled there, neither remnant populations nor technological artifacts survive on any of the Physalian Worlds. Back at home, their understanding of Ceratium, Ceratophorus has regressed back to a pre-scientific level, while Physalia has been completely forgotten.
For the Horizon System’s current spacefaring inhabitants, the situation is much different. The biological diversity of the Physalian Worlds exceeds that of all the planets of Actinophrys combined, making them an exceptionally attractive target for biomechanical industry. Though the inner ones remain largely untouched due to their extreme hostility to most life, the outer Physalian Worlds are today home to thousands of uniquely adapted cities, outclassed in sheer variety only by the frontier center of Amazonia. Hundreds of species from across the Physalian Worlds have been uplifted into sapience by the spacefaring Horizonians, from the soaring jet-darters of Athorybia to the neural jellyfish of Eudoxoides. Many can now be found thousands of light-years from home, bringing the will of Horizon to strange new worlds.
Myriad Celestia: Nature, Red in Tooth and Claw (The Physalian Worlds)
Physalia is orbited by twenty planetary-mass bodies large enough to collapse into spherical shapes, twelve of which support some form of life on their surfaces. While these are ‘planets’ of the brown dwarf, they have much more in common with the moons of Rhodactis and Olindias than, say, the Actinophyridan Worlds. Their orbits and masses span several orders of magnitude, resulting in an incredible diversity of environmental conditions that has encouraged an enormous variety of strange organisms to evolve, making use of even the weirdest and most hostile habitats to their full capacity.
A. The Rhodaliid Series
From left to right: Dromalia, Mistoprayina, Arancialia, Nectadamas, Dendrogramma (Agalmatid Series), Thermopalia
Stephalia is not visible at this time.
The worlds of the Rhodallid Series are hellish like no other. While Chrysaora, Elysia, or Resomia might be hotter, few places are so utterly inimical to life as we know it as they. From the near-vacuum, obsidian-bladed mountains of Arancialia to the constantly-exploding surface of Thermopalia, these six hateful worlds seethe with tidal fury. Volcanoes remake their surfaces on a yearly basis, while choking clouds of sulphuric acid, hydrogen sulphide, and volcanic glass bear down on barren rock. Worse still, Physalia’s magnetosphere bathes these horrid planetoids with enough radiation to kill even the hardiest microbe and scour even radiation-hardened electronics. Perhaps there truly are places in the universe where life was never meant to go.
IA. Thermopalia
This aggressively hostile world heads off the Rhodaliid Series, doing its best to kill you in as many ways as possible. Though slightly smaller and less massive than dead, silent Mercury, Thermopalia sustains an atmosphere about as thick as Earth’s. The high temperatures rapidly strip this extended atmosphere away but constant globe-spanning volcanism liberates toxic gases from its mantle just as fast as they are lost. Thermopalia is bombarded with enough ionizing radiation to kill anything and everything and spark flickering, ultra-bright aurorae across all of its surface. With low gravity and extreme volcanism, ‘verneshot’ events where tremendous gas explosions cause chunks of crust to be shot into space and back are not uncommon, resulting in a constant high-velocity rain of meteors that heat the atmosphere to a simmering boil.
IB. Dromalia
Lying in roughly the same orbit as Thermopalia is a small, molten terrestrial world. With three-fourths the gravity of its sibling and about 86% the mass, Dromalia has a lower outgassing rate and thus has only about half as much atmosphere. Nevertheless, it is a dynamic, active, and ruthlessly hellish planetoid. Though Thermopalia’s metal-rich surface has the decency to remain at least somewhat solid under the immense tidal stress, Dromalia’s crust has thoroughly exploded to reveal the sea of magma beneath.
IIA. Arancialia
Though this barren world is orders of magnitude less hostile than its inner neighbors, it is in no way a livable place. With slightly less mass than the Moon, Arancialia should have long ago cooled off and became covered in craters. Instead, volcanic calderas and tectonically lifted mountains dominate its surface, while an atmosphere similar to Mars’s fills the lower basins. Huge tracts of the surface are covered in glassy obsidian from explosive eruptions, which climbs into spindly, razor-sharp spires in the low gravity. Though it receives only 4% as much tidal heating as Thermopalia does, this is still over 150 times as much geothermal heat as Earth has to work with. With a day only seven hours long, blistering sandstorms fast enough to grind rocks to dust are a common sight on this desert hell.
IIB. Stephalia
By far the smallest member of the Rhodaliid Series, little Stephalia is a world on the edge. This 700-kilometer ball of rock is just barely large enough to crush itself into a sphere; any smaller and it would be an asteroid like our Vesta or Pallas. Even this tiny world is an active one; though its primordial heat has long run out, tidal deformation generates enough energy to melt some subsurface pockets of magma and slowly reshape its surface, while irradiated sulphur tinges its rocky surface a deep crimson.
III. Nectadamas
At just over the mass of Mercury, Nectadamas is the second-largest member of the Rhodaliid Series and one of only three Physalian Worlds mostly made of carbon. Nevertheless, it is not all that different from its rockier siblings. Enormous amounts of carbon dioxide and methane in the atmosphere raise the surface temperature to incredible levels, partially melting the carbide crust. Clouds of boiling gasoline shroud an acrid surface of blood-red sulphur lakes, graphite plates, and deserts of chromatic diamond dust. Though the clouds unleash a constant deluge of petrol rain, all of it boils long before reaching the bone-dry surface.
IV. Mistoprayina
In the outermost regions of the Rhodaliid Series is its largest member, a hellish carbon world 88% the mass of Mars. Though it is most distant of all the Rhodaliid Series, Mistoprayina experiences by far the most tidal heating due to its relatively large size. Comparatively high gravity and extreme volcanism have caused Mistoprayina to form an immense atmosphere some 75 times thicker than Earth’s. Powerful updrafts suspend a thick layer of carbonaceous soot high in the atmosphere that casts the surface in almost total darkness, lit only by the distant torchlight of giant volcanic eruptions.
B. The Agalmatid Series
From left to right: Abyla, Nectadamas (Rhodaliid Series), Athorybia, Diphyes, Nanomia
Dendrogramma, Sphaeronectes, and Tottonophyes are not visible at this time.
Beyond the hostile tidal hells of the Rhodaliid Series is a heterogenous intermediary region. While the seven members of the Agalmatid Series remain distant enough from Physalia to avoid exploding, still-frequent volcanism causes them to accumulate thick greenhouse atmospheres rich in carbon dioxide and water. Surface temperatures generally range between 50 and 150°C, while surface pressures can reach hundreds of atmospheres. Though the radiation is far more survivable than in the Rhodaliid Series, the upper atmospheres of the Agalmatid Series are still radioactive enough to kill all complex life, forcing their natives to hide in the narrow strips of sky between the crushing, volcanic lower hell beneath and the freezing, radioactive upper hell above.
V. Diphyes
With only 70% the mass of Mars and surface temperatures approaching 100°C, one might expect Diphyes to be a barren rock. Instead, we are met with a lush, pressurized, oppressively humid world teeming with strange life. The boiling lowland seas and lakes are maintained by an atmosphere over 100 times thicker than Earth’s, while constant volcanic eruptions fill the atmosphere enough smog to blot out over 99% of the sunlight that falls on the planet. Above thick storm clouds of water and sulphuric acid, the freezing upper atmosphere is bombarded with enough ionizing radiation to kill even the hardy tardigrade.
Though by our standards Diphyes is wildly hostile, life has found a way. Banks of black, radiotrophic plankton venture into the inhospitable upper atmosphere, using abundant UV and x-ray radiation to photosynthesize. They inadvertently shield the warm, wet cloud decks below, fostering great tangles of neuron weed and orbuline heliophytes. Frequent volcanism injects nutrients into the atmosphere in the form of volcanic ash, sustaining huge blooming clouds of aeroplankton that feed everything from giant air whales to trillion-strong flocks of engrauliopteran sky-sardines. Particular to Diphyes are huge swarms of bio-blimps - colonial, hydrogen-buoyed balloon lifeforms ranging from football-sized to over a hundred meters long.
Diphyes’s lands and seas are virtually inhospitable. They are pelted constantly with steaming rain and scoured by apocalyptic lava flows while vapors of hydrogen sulphide and hydrogen cyanide make the surface toxic for most organisms. However, even this flaming, pressurized hell has its inhabitants; black, thermophilic megabacteria use hydrogen sulphide to perform chemosynthesis, forming tiny forests with their own cast of miniature creatures on every fresh volcanic barren.
VIA. Nanomia
Though around the same size as Mars, Nanomia contrasts starkly with its Solar System counterpart. Nanomia is depleted of water but enriched in ammonia, resulting in a thick but dry atmosphere dominated by molecular nitrogen. Vast deserts of barren rock hot enough to fry any lifeforms foolish enough to traverse them separate the planet’s hypersaline lakes and seas, while the majority of its water is locked up in global clouds. Nanomia’s dry air warms and cools quickly, resulting in severe temperature differences between its day and night sides that drive permanent, globe-spanning, hurricane-force windstorms. Unlike Mars, which is largely devoid of geological activity, tidal heating brings Nanomia to a boil; Plinian eruptions punch through the cloud decks as pyroclastic surges bring ruin to the provinces nearby. But even in such oppressive conditions, life persists on Nanomia.
Though the Nanomian atmosphere is violent, complex life thrives with a suite of unique adaptations. Drier atmospheric conditions force most organisms to cover themselves in watertight exoskeletons or dermal scales; siliceous, crystalline chandelier-plants replace hydrogen-buoyed algal mats while reptilian and arthropod-like fliers replace jellyfish- and mollusk-like ones frequent on Diphyes or Athorybia. They have developed a unique form of bio-graphene foam which they use to trap lifting hydrogen. This passive flotation method is very efficient and robust, allowing fliers from millimeter-scale acarobalanoidean barnacle mites to the predaceous, 50-meter dragonwing sky-serpent to take to the skies for all their lives.
On the ground, conditions are a bit more habitable than the hellish surface of Diphyes. Rain-soaked mountain ranges and cool lakeside soils are home to stands of giant radiator-trees and a wealth of arboreal fauna, while swift, metallic spider-things scurry across the searing deserts on filigree legs, feeding on the steady stream of stone-seared corpses falling from above.
VIB. Sphaeronectes
This tiny world closely resembles a slightly larger and drier Ceres. With small size and only small amounts of tidal heating, this world’s surface bears the scars of millions of years of great impacts. Nevertheless, the gravitational squeeze of Physalia maintains a weak flame in its core, enough to fuel a few cryovolcanic domes across its surface.
VIC. Tottonophyes
At just 800 kilometers across there is little that distinguishes this small world from all the other asteroid-pelted rocks in the Horizon System save for its composition. Tottonophyes is made almost entirely out of the element carbon, lacking even the carbide rocks of Nectadamas and Mistoprayina. Much of its deep interior is thus crushed into a single, contiguous diamond.
VII. Abyla
With a surface pressure of ‘only’ 54 atmospheres, Abyla is much less exotic to human sensibilities than its fellows in the Agalmatid Series. Despite this, it is still a pale comparison to Earth - choking CO2 and SO2 hazes fill the lower valleys, the surface gravity is less than half hours, the seas are a toasty 60°C, and the surface is plunged into perpetual twilight due to a globe-spanning blanket of biogenic clouds. Like Panthalassa, Abyla’s crust is a messy agglomeration of continental blocks interspersed with great ridges, which on this more terrestrial world manifest in crisscrossing, ribbon-shaped continents and sky-piercing mountain chains.
Unlike most of the other Physalian Worlds, Abyla’s complex life is home-grown, having evolved in just the last 60 million years. Unlike on Earth, where animal life would not step onto land for another 40 million years, the Abylan continents have already gotten started on developing their own unique fauna. Thick microbial mats intermingle with reefs of pagoda-sponges, fields of armored featherworms, and forests of thalassocardian star-hearts that can sometimes rival small mountains in height. These hazy dreamlands are populated by various strange mobile animals from multi-headed aciculognathan needleworms to one-footed pogo-urchins to vast, oceangoing kraken, but for all their oneiric strangeness life on Abyla is still very much in the early days of figuring out how to be a functional ecosystem.
The atmospheric life of Abyla is relatively unimpressive. Most of the oceanic animals haven’t figured out how to swim, let alone fly, so the atmosphere is largely filled by passive drifters. But this is not to say that atmospheric lifeforms are few in number. From space, the helium-filled cells of angel’s eye algae and the filigree tendrils of siphonophoran curtain-nettles blanket Abyla in a continuous envelope of viridescent chlorophyll which plunges its antediluvian surface into eternal gloom. One day, the appearance of active fliers will result in a new evolutionary arms race, but for now it is the calm before the storm.
VIIIA. Athorybia
At some 40% the mass of Earth, hot-pink Athorybia is the largest and quite possibly the weirdest of all the Physalian Worlds. Though it is the most distant of the Agalmatid Series, its large size and eccentric orbit cause intense tidal volcanism that builds up an atmosphere over 700 times thicker than Earth’s. Under these conditions, Athorybia’s carbon dioxide-rich atmosphere is a supercritical fluid, smoothly transitioning from atmosphere to ocean. This supercritical ocean covers all of the planet’s surface save for its highest mountains, heating the surface to a uniform, toasty ~90°C. At the very bottom, proper seas of water lie in the eternal dark at the bottom of the carbon dioxide abyss, like brine pools at the bottom of our own deep oceans. Far above the bubbling, intangible surface of the supercritical CO2 ocean is a global blanket of water clouds which host their own menagerie of strange life.
The main cloud deck lies at a temperate 30°C and a pressure of around 30 atmospheres, equivalent to that 300 meters under our own seas. Flying here is quite like swimming, forcing atmospheric organisms to evolve a strange repertoire of adaptations. Gas-bladders and rain-catching filaments are salient features, while wings are reduced to fin-like appendages to better row through the soupy air. Titanic jellyfish-like drifters 500 meters or more can sustain whole ecosystems on their backs, while huge intertwined reefs of bio-graphene foam and living vegetation can form kilometer-scale islands host to their own unique cast of arboreal creatures who live their whole lives tens of kilometers off the ground. A whole host of weird fliers from stegopteran platewings to string-of-pearls flagellophysans to pristacanth sharkbirds populate these atmospheric rainforests, which boast a level of biological diversity equivalent to those of their terrestrial counterparts.
Far below the clouds, a literal shadow biosphere lurks. All sorts of abyssal creatures lurk in the oxygen-rich supercritical CO2 ocean, which can be breathed with little ill effect. Many, like the pithotestacean bottle-ships and asteropteran sky stars, feed on organic matter falling from the sky above, much like how hordes of detritivores harvest marine snow in our oceans. Other species rise into the upper layers to feed under cover of darkness, unfurling fins into wings and raising their metabolisms to fly in the gaseous air of the canopy. Horrific forms from wide-mouthed stomosome balloon worms to schooling, eusocial Formicosaurus harvest the flesh of the rainforest inhabitants every 32-hour night before retreating back into the depths lit only by the faintest trickle of sunlight and the bursts of lightning and bioluminescence.
Even deeper down, yet stranger forms lie. Conditions at Athorybia’s sea level are similar to those at hydrothermal vents in Earth’s deepest marine trenches. Vegetation consists of colonies of chemolithotroph microbes, while animal life from tumbleweed-like cystocomids to reedy calamobrachid spider-hounds is universally slow and ponderous. Like giant isopods and snailfish at the bottom of Earth’s abyss, the surface fauna of Athorybia are adapted to extreme nutrient scarcity, making use of the tiny fraction of organic matter not caught and eaten by atmospheric lifeforms. Volcanic vents and the occasional fallen corpse of an aerial leviathan are flush with life, like tiny oases of bioavailable energy in an endless biotic desert.
VIIIB. Dendrogramma
Little Dendrogramma distinguishes itself by being the smallest and least massive habitable world on this side of the known universe. It is significantly smaller than most of the aquarian moons of Rhodactis and has a surface gravity only a third that of Earth’s. With a mass approximately equal to that of Mercury, Dendrogramma remains habitable and geologically active only thanks to the tidal heating of Physalia. Due to its small size, the tidal forces it experiences are only moderate, allowing it to sustain mild surface conditions similar to those of Cretaceous Earth. It is the only member of the Agalmatid Series to have conventionally habitable surface conditions.
Low gravity and weak winds allow plant life to grow impossibly tall; Dendrogramman tube-trees often reach heights up to two kilometers, enough to generate their own weather formations. Vegetation absorbs essentially all sunlight before it reaches the forest floor, resulting in an ecosystem structured more like Earth’s oceans, with sunlit, twilight, and midnight zones. The photic zone of Dendrogramma’s ‘green sea’ is home to a tremendous array of arboreal megafauna, from gliding tree lobsters and megaspiders to roving packs of wolfworms and horrific cephalopodous wind-walkers. In the twilight zones below, armored, slug-like cystolepadids graze on shade-loving mosses while bioluminescent lophisaurs snag overly-curious fliers, while in the eternal dark of the understories moonflower stars systematically pick the shaded branches for prey. Unlike the practically barren seabeds of Athorybia, the forest floors of Dendrogramma are an energy-rich environment covered in a slime of organic material seething with blind scavengers and marooned parasites.
C. The Prayid Series
From left to right: Physophora, Apolemia, Lilyopsis, Eudoxoides, Stephanophyes
Sulculeolaria and Rosacea are significantly inclined to the remainder of the Prayid Series and do not participate in alignments.
The last series of the Physalian Worlds is a set of seven habitable worlds. The members of the Prayid Series are a set of temperate oceanic terrae distributed between 2 and 20 million kilometers out from Physalia with masses between 10% and 30% Earth’s. Despite their apparent similarity to each other and to the other Physalian Worlds, each and every member of the series is strikingly unique - from storm-lashed Eudoxoides to artificial Stephanophyes to smog-choked Lilyopsis, unique selective pressures and a severely limited selection of seeder lifeforms has transformed the Prayid Series into a truly wonderful display of biological splendor.
IX. Apolemia
With 8.5% Earth’s mass and 40% the gravity, Apolemia is fairly similar to its inner neighbor Dendrogramma. Both straddle the lower bound of habitability with their exceptionally low gravity and rely on the tidal squeezing of Physalia to maintain tectonic activity and habitable surface conditions. However, Apolemia is poorer in water and cannot sustain the huge global forests that blanket its inner neighbor; patches of dense vegetation give way to vast prairies and subtropical savannas on this comparatively cold world.
Apolemia is the home of some of the largest naturally-evolved fauna known to science. The insect-reptilian ‘Arthrosauria’ that dominate most of Athorybia’s ecosystems can be as much as three times longer and twice as massive as the largest blue whales. Though their appearance may suggest otherwise, these are not primitive animals but rather some of the most specialized and sophisticated forms in the entire Horizon System. The arthrosaurs display the haplodiplontic life history common to all Horizonian higher fauna, but their diploid sporozoa also undergo a series of gradual metamorphoses like amphibians or some dinosaurs, allowing a single species to occupy numerous ecological niches. Like some salamanders, many arthrosaurs can produce spores in ostensibly ‘juvenile’ stages if local conditions are unsuitable for their titanic adult forms, so some ‘species’ of large arthrosaurs may seemingly go extinct for decades or centuries before suddenly reappearing once conditions are once again suitable. The savannas of Apolemia, struck with the sounds of unearthly bellows and the booming march of titans, surpass anything Jurassic Earth may have to offer.
X. Eudoxoides
Though its bulk properties are nearly identical to those of Mars, Eudoxoides could not be more different from our red planet. This small world’s surface is covered by a deep global ocean from which protrude only scrappy microcontinents and the mouths of huge shield volcanoes (a la Olympus Mons). With no major landmasses and globally tropical conditions, Eudoxoides is permanently beset by hundreds of hurricanes and tropical storms, which can grow as large as the continental United States and last for decades or even centuries. Battered by constant rain and blistering winds, only the constant roar of island-building volcanoes prevents this world from drowning in its own seas.
Like Abyla, Eudoxoides’s fauna does not descend from multicellular Horizonian ancestors, having last shared a common ancestor with the Neozoan fauna of the other Physalian Worlds some 1 billion years ago. By contrast, the Eudoxoidean flora does belong to a foreign lineage who arrived some 200 million years ago via Dendrogramma. The fauna has only been in existence for some 90 million years and so most life is still aquatic and of flatworm-grade complexity, but the moist, storm-battered landmasses are easy enough for more robust aquatic animals to colonize. Hydrogen-buoyed jellies flutter through the foamy bogs of the inland deltas and vast stands of algal forest like overgrown pond scum creep up rivers, while armored slugs and skittering myriopteran aquapedes take their first crawling steps out of the water, oblivious to the evolutionary explosion that their descendants will beget.
XI. Physophora
Though arguably the most Earth-like of the Physalian Worlds, Physophora is a strange world with a tenth the mass, half the gravity, thrice the atmosphere, and a ten-times-longer day. Neither the weak tidal forces of Physalia nor its own feeble geothermal heat are able to break Physophora’s strong crust, so plate tectonics is entirely nonexistent. Instead, the planet has a Venus-like geography scattered with random hotspot islands, resulting in a disconnected, broken land arrangement divided by shallow seas. In essence, Physophora is the Indonesian Archipelago but extended to cover a planet’s entire surface.
While most of the other Physalian Worlds are home to at least a few distinct faunal lineages, Physophora is unique in that its entire fauna descends from a single derived lineage of Horizonian life - the cephalopodic Monocephala. While on Horizon their lifestyles generally resemble those of ammonites, octopuses, and feather-duster worms, on Physophora they have been able to fill every role in the ecosystem in the absence of competing species. From masses of rudist-like reef builders to many-legged saurians to microscopic parasites, the fauna of Physophora is a testament to the power of evolution; even a single lineage can give birth to a world of wonders if given the opportunity.
XII. Stephanophyes
With a minimum distance from its host of well over 5 million kilometers, Stephanophyes is the first of the Physalian Worlds which receives negligible tidal heating. As such, it can only rely on its own supplies of geothermal heat to power the geochemical cycles which keep its climate habitable. Fortunately for its inhabitants, Stephanophyes is well over twice the mass of Mars, large enough to sustain active plate tectonics for all of the planet’s habitable lifetime. With no particularly unusual climactic features besides a day eighteen times longer than Earth’s, one might expect Stephanophyes to be relatively uninteresting compared to the weird and wonderful environs of the other Physalian Worlds. Such an assumption could not be further from the truth.
Stephanophyes’s fossil record is an enigma. For 1.5 billion years nothing more complex than bacterial scum called this planet home before complex life abruptly appeared some 200 million years ago. While a particularly fast diversification event might plausibly produce this pattern, many details of the modern fauna show that this explosion of life was anything but natural. Many Stephanophyan microbes use impossibly optimized biochemical pathways, while others are interplanetary genetic hybrids of lineages separated by millions of miles of vacuum and billions of years of evolution. The same holds true for macroscopic life, while many of the larger organisms have been reshaped to resemble lifeforms from far-off worlds, from the Anomalocaris of Cambrian Earth to the Mecistotyrannus of Membracian Clinochlore. The identity of Stephanophyes’s demiurge is unknown; the only comparable work of bioengineering in the known universe is Amazonia, which is a far more ambitious project than this.
XIII. Lilyopsis
Lilyopsis is a world out of place. Despite receiving negligible tidal heating and having only twice the mass of Mars, it hosts a thick and soupy atmosphere that would not be out of place in the Agalmatid Series. The atmosphere contains little oxygen and significant concentrations of several reducing gases, most notably hydrogen sulphide, methane, and hydrogen. This mixture would likely be explosive were the concentration of oxygen any higher, but as it stands Lilyopsis maintains an uneasy chemical equilibrium. Visually, this unusual atmosphere manifests as a viridian haze which blankets the lands and seas of this world.
Life on Lilyopsis is critical for the maintenance of its unusual atmosphere. Unlike every other planet in the Horizon System, Lilyopsis is home to macroscopic aerobes and anaerobes. The dominant flora of this world are lichens which perform anoxic hydrogen-sulphide photosynthesis, while oxygen-producing plants are the minority. Each type of flora is dependent on the other’s emissions for vital metabolic processes, maintaining the uneasy equilibrium between them. The fauna has evolved accordingly, using both aerobic and anaerobic respiration to survive. Even still, the atmosphere is so poor in oxygen that even this combined metabolism cannot support very active animals. The megafauna thus consists mostly of slow-moving beings similar to overgrown nematodes and millipedes. So long as Lilyopsis’s air remains stale, it will be a world for the worms and the worms only.
XIV. Sulculeolaria
At some 13 million kilometers from Physalia, Sulculeolaria completes its orbit once in a sluggish sixty-five days. As it is tidally locked to Physalia, its day is about as long, the suns creeping through its sky at a glacial pace. Though broadly similar to Earth, Sulculeolaria’s slow rotation allows heat to move easily across its surface, evening out the temperature so that neither tropical rainforests nor arctic tundra may exist. Its continents are covered by vast swathes of temperate forest bounded by bands of cool desert at the poles. Though temperatures may push 40°C during the days-long ‘noon’, even the equator is blanketed by snow in the dead of the cold night. No other world in the Horizon System experiences comparable conditions save for Praya’s outermost planet Crystallophyes, which has a depauperate biota mostly devoid of large flora and fauna.
Life on Sulculeolaria has several strategies to deal with the long days. Small plants generally complete their life cycles in the time from sunrise to sunset, surviving the month-long night only as resistant spores. Larger vegetation follows a daily hibernation cycle like the Metasequoia forests of Eocene Canada, photosynthesizing throughout the day then dropping their leaves and entering dormancy to survive freezing nighttime temperatures. For more mobile animals, another option exists. An animal at the equator which sustains an average speed of 16 kilometers per hour can outrun the night, while even slower creatures can keep pace further towards the poles. Cetaceous sea slugs, elephantine land-arthropods, soaring sky-spiders, and a whole host of strange megafauna partake in this eternal march - endlessly chasing the blooms of fresh vegetation at the planet’s morning band as a whole migratory ecosystem.
XV. Rosacea
The last of the Physalian Worlds is a kind sea home to wondrous sailing forests. Save for a few scrappy volcanic archipelagos, the deep seas of Rosacea stretch on uninterrupted for thousands of kilometers. Though such deep oceans would normally be barren of life, the cold temperatures of Rosacea enhance thermohaline circulation, pulling dissolved minerals emitted by deep-sea volcanoes up into the surface waters. Though Rosacea’s orbit around Physalia is nearly five months long, the tidal forces it experiences are far too weak to lock its rotation, resulting in a reasonable day length of about 20 hours that ensures mild climates across the globe.
The vast plumes of nutrients that innervate Rosacea’s seas fuels the growth of a unique ecosystem. Floating forests of spongy, conifer-like plants can rise up to fifty meters above the waves, their long roots acting both as anchors and nutrient siphons. Their clonal colonies can aggregate into great reefs hundreds or even thousands of meters across, drifting through the vast oceanic gyres alongside vast tangles of floating seaweeds and filter-feeding invertebrates vaguely similar to the sargassum forests of Earth’s seas. These seafaring jungles are home to a huge diversity of life, from amphibious eelworms to driftwood anemones to vicious amphisaurs on an endless voyage through the deep blue sea.
