The Horizon System: Changxing, a Broken-Glass Rose
Darwin
Changxing (Temperate Marine Superterra, Planet)
System - Horizon-Actinophrys
Mass - 2.019 Earths
Radius - 7,649 kilometers (1.199 Earths)
Global Average Temperature - 26.26°C
Day Length - 19h 2m 8.8s
Year Length - 2.019 years
Number of Satellites - 19
ESI - 0.909
Etymology - After the Changhsingian Age, the last stage of the Permian Period that would culminate in a devastating mass extinction that would kill off some 90% of animal life and usher in the Age of Reptiles.
Overview
At the core of the Resonant Worlds is the only true Earth analogue in the Horizon System. With two times Earth’s mass, a warm, wet surface dotted with countless islands and a supercontinent cut through with shallow inland seas, a powerful magnetic field, and an atmosphere rich in oxygen, it might even be sufficient to call Changxing a super-habitable world, rife for habitation by countless strange and wonderful lifeforms. As the only one of the Actinophryidan planets which has been and will remain habitable for Actinophrys’s entire main-sequence lifetime, it would seem like a perfect habitat.
But even though Changxing has life, it is far emptier than it should be. Where there ought to be tropical forests teeming with life, there are rocky barrens host only to riverine algae. Where there ought to be temperate woodlands and lush steppe, there is only empty desert. In the oceans, where there ought to be grand reefs and fields of seagrass, there are only flat, elephant-skin plains of microbial slime. The only sign that once-great plants and animals once populated this world are petrified trunks and scattered, ancient bones - testaments to a hazily-remembered not-so-prehistory.
Something catastrophic happened here, that is for sure. But what could possibly lay a living world so low?
“So now that you failed to incite a popular uprising, you turn to the underworld for help? It’s a decent strategy, though not one my fellows would take kindly to. Though I in my flagrant violation of this Imperium’s order may seem like a suitable ally for your insurgency, you have made one critical mistake here.
My enterprise exists only because there is an order to subvert. What you would have me do would ensure its destruction no matter what shortsighted gains I may glean from the chaos you cause. And I very much enjoy my enterprise, intruder. You would stand to learn that.“
- The Fourth Archon, “Inconvenient Queries Of Unconventional Ethics“, “Unofficial Response to the Request for Aid in the Horizonian Overturn“ (2239)
Lifeforms
Though Panthalassa and even Cryogenia get considerably higher ratings on the Earth Similarity Index, neither resembles Earth nearly as much as Changxing. The only biologically meaningful differences are a shorter day, a somewhat higher obliquity, 40% more gravity, and a few extra moons - it is the only planet in the Horizon System whose atmosphere is even remotely breathable for humans. With its large size and warm climate one might even call Changxing a super-habitable planet, but it is strangely empty.
The reason for Changxing’s odd state is revealed at close inspection. Though not pristine, some ten fresh large impact craters scar its surface, the largest of which is thrice the size of Chicxulub. All of these date to around 10 million years ago, the same time that Changxing’s relatively fresh ring system was formed. These impacts correspond with an apocalyptic extinction that divides its Therozoic Era from the current Neozoic Era, which caused the extinction of over 99% of all life.
Changxing once had global forests of green plants descended from a lineage of Horizonian algae, but all terrestrial plants went extinct in the end-Therozoic extinction. Today, the land is dominated by reef-like formations of giant lichens, terrestrial algae, and photosynthetic animals. The only higher Changxingian plants to survive into the Neozoic are riverweed-like aquatic flora, highly degenerate forms that hardly resemble their extinct relatives whose incinerated remains are still eroding out of rocks around the world. In the oceans, the only phototrophs that survived are unicellular algae, stromatolites, and a few species of zooxanthellate animals and macroalgae from murky river mouths and the deepest parts of the photic zone.
Animal life has fared even worse. During the Therozoic, Changxing was dominated by the Horizonian group Squamatozoa, a phylum of animals that vaguely resemble earthworm-lizard hybrids. Megafaunal niches on land and sea were almost exclusively occupied by members of this phylum, which diversified into nearly a million species ranging from mite-sized to sauropod-sized. All of them were wiped out in the end-Therozoic extinction with the exception of a few eutelic, tardigrade-like forms, leaving Changxing with no animals longer than one centimeter in length. While most of the surviving fauna remains very small, enough time has passed for a select few to try their hands at megafaunal size. The seas now swarm with strange things ranging from paddling anemones to one-finned sea-elephants to giant, chandelier-garnish amoebas, while on land creatures of all sorts from hopping slinky-beasts to wheeled urchins portend the arrival of a new, much stranger era in Changxing’s storied faunal history.
Past & Future
Like most of the other Resonant Worlds, Changxing began its life as a small mini-Neptune whose thick primordial atmosphere was ripped off by the point-blank blast of a supernova shortly after it was born. A titanic collision with a Mars-sized protoplanet liberated a small amount of material from Changxing’s water-rich mantle that condensed into four Ceres-sized moons Bonarelli, Lau, Mulde, and Ireviken, as well as an unknown number of inner asteroid-sized ones. This arrangement remained stable for nearly 1.7 billion years, but it was doomed from the start.
10 million years ago, Changxing’s innermost large moon Bonarelli and several of its asteroid moons drifted into a secular resonance with each other, causing the inner moons to become unstable. All of them save for the outermost Emeishan and Warakurna were ground to dust in a series of giant collisions, pelting Changxing with kilometer-scale fragments and forming its bright, dusty ring system. The remaining thirteen inner asteroid moons Changxing has today condensed from the largest fragments of those collisions, delineating gaps and bands in the rings that give them their distinctive shape today.
But the calamity that befell Changxing is not fully over. Many of the inner asteroid moons are still close to secular resonances with Bonarelli and Lau which will continue to destabilize their orbits and cause giant collisions between them. In particular, the medium-sized asteroid moons Whitsunday and Sierra Madre will collide with each other within the next million years, possibly causing another minor extinction event then.
Civilization
The end-Therozoic extinction occurred too early for the civilization of Old Horizon to witness either the pre-extinction fauna or the ruined, burning world that existed immediately after. Since Changxing’s current appearance is not too obviously different from that of all the other inhabited Horizonian worlds, the first signs that anything was wrong with it came after robotic probes were sent to investigate its ecosystem, upon which its peculiar dwarfed fauna and flora and the fossilized remains of their predecessors were discovered. This also meant that Changxing’s role in Horizonian culture came to prominence long after the romantic visions of the other planets vanished amid an increasingly scientific vision of their properties. Many of the literary roles previously attributed to Riftia or Panthalassa now shifted to a prehistoric version of Changxing, which authors imagined hosting intelligent beings whose arrogance or negligence brought down the skies upon them. Ironically, such cautionary visions would not save Horizonian civilization from collapsing itself some hundred thousand years afterwards.
Today, the prophetic literary vision that was Changxing during Horizon’s golden age is remembered all the more deeply by their civilization’s remnants. The celestial cause of the end-Therozoic extinction has morphed into a story of divine retribution for mortal arrogance. The literary trope of a Changxingian civilization which through their own arrogance invited their own destruction has become an accepted fact in all remaining Horizonian communities, who now draw a comparison between this alleged civilization and the one built by their own ancestors, a comparison made all the more relevant by the fossilized remains of their ancestors’ megacities that they continue to inhabit.
Changxing is of great scientific interest to spacefaring Horizonian civilization, as the process of biological recovery on a nearly-sterilized planet is similar to the initial establishment of life on a newly-terraformed one. Speculations on the immense biological diversification event that is beginning to happen on Changxing are common in popular literature, while some particularly ambitious bioengineers have attempted to realize these speculations or bring the lost world of prehistoric Changxing back to life. Despite this interest, Changxing is completely uninhabited by sapient life; the entry and exit of biological materials from its surface is strictly regulated by the system authorities in order to prevent introduced species from establishing a foothold on this empty world.
