EPONA

by Wolf Read

     What is Epona? Depending on how you approach the question, not an easy query to answer without hauling around a thick stack of notes. Basically, Epona is a strikingly detailed fictional alien world. How detailed? VERY. A Webster's-sized dictionary might be enough to contain all the textual information amassed on Epona; and this grossly ignores the hundreds of Eponan art pieces detailing the world, from ink illustrations and paintings, to computer generated renderings and animations to sculptures. Quoting Larry Niven, who had a chance to view an Eponan interactive computer demo, "I have never seen a playground this size."
     Epona's development was begun by Martyn Fogg, formerly an editor for the Journal of the British Interplanetary Society, possessing an interest in world engineering processes (among other things). On an Archimedes RISC-based computer, he's generated thousands of planetary systems via the particle method. Epona and her sister worlds were born from this computer.
     Actually, Martyn Fogg is just part of the story. The actual genesis of Epona came from a project created by members of CONTACT a nonprofit educational organization with roots in science fiction. An article on CONTACT, written by Greg Barr, appears in a1993 issue of Analog Science Fiction/Science Fact. This wonderful experiment was called Cultures of the Imagination, or COTI. People participating in COTI are divided into two groups. One group creates an alien world with a sophont while isolated from the second group, which builds human history to the point of starflight. Development proceeds for three days during the annual Contact conference, and at the end, a first contact is simulated between the two isolated groups. Lots of fun.
     After taking part in a COTI session, people sometimes mentioned that three days was not enough time to significantly develop an alien world and culture. Martyn Fogg, one of those people, decided that, instead of three days, why not have a development session stretch out over three years? Getting together with Greg Barr, who was at that time the CEO of Contact, a regular newsletter for the Epona project was created, inviting Contact participants to join in the long-term development of an alien world. Many people, such as myself, responded, including artists, biologists, chemists, astronomers, anthropologists and science fiction writers. The amount and variety of Eponan ideas, their interconnectedness, and the solid scientific detail supporting the framework was entirely unexpected.

EPONA'S FAMILY OF WORLDS
     Epona is the third world of nine which circle the star Taranis, originally 82 Eridani. Taranis is a yellow dwarf (G5 V main-sequence) star that is roughly 5 billion years old. As its original name implies, the star resides in the constellation Eridanis, and currently drifts in its galactic orbit some 21 light-years from Sol.
     The four inner planets of Taranis, including Epona, are terrestrial in nature, being small, ranging from 0.1 to 2.0 Earth masses in size, and having average densities within the range of rock, from 3.8-6.4 g/cm3. The inner two worlds, Belenos and Grannos respectively, are similar to Mercury, with small bodies, high densities and little in the way of atmospheres. The large chunks of rock are tidally locked to Taranis, and Grannos' long ago atmosphere has been frozen into carbon dioxide ice on its night side. Epona follows, with a mass of 0.55 Earth's, an oxygenated atmosphere that averages 0.577 bar at the surface, continents of silicate rock, temperate climate and seas of water. The fourth world, Sucellus, with a high density of 6.4 and mass of 2.0 is a sizable terrestrial world, with a carbon dioxide atmosphere of roughly four bars and a surface covered in a deep ocean.
     The next four planets are a family of gaseous giants, with huge masses, from 5.9 to 206 Earth's, and light densities, all sitting around 0.7-2.4 g/cm3. The fifth world, Rosmerta, is the smallest of the family, a mini gas giant with a viciously hot world-encircling ocean being sustained under an equally challenging atmosphere that exceeds 1,000 bars in pressure. The small gas giant is followed by the largest, Borvo. Borvo is 65% the mass of Jupiter and is similar in nature, producing a powerful magnetic field, tightly holding a vast array of moons and presenting a surface of seething storms. Bormo, world number seven, is similar to Uranus, even possessing a strong axial inclination of 73 degrees. Bormanus, the eighth planet from Taranis, is similar to Saturn in density and mass. This icy-ringed world follows the most elliptical path of Epona's sister planets, maintaining a mean eccentricity of 0.16.
     The final world, Sirona, is Tritonian, being comprised of ices, though it is more massive than Mars. Occasional cryovulcanism maintains a thin atmosphere of nitrogen, methane and hydrogen.

EPONA'S GEOLOGY
     Epona accreted a similar distance from Taranis as the Earth did from the Sun, so the composition between the two worlds is quite alike. Epona has a lower abundance of heavy elements, accounting for a lower density. During the first 3.3 billion years of existence, Epona possessed a liquid iron-nickel core, a convective asthenosphere and shifting lithospheric plates.
     Epona's tectonic activity did not last as long as it has on the Earth. Being a smaller world, Epona has a higher surface to volume ratio than the Earth, and thus has had its store of internal heat dissipated at a significantly faster rate. Nearly two billion years ago, Epona's tectonism began to slow, and later froze up completely as the lithosphere continued thickening. Many types of mountain building stopped, and continental masses simply began weathering and eroding away. Habitability: Maintained by a Cycle
     Highly weathered continents are okay as far as Epona's biome is concerned, but breakdown of tectonism has one major side effect for life. Epona's dead geology severs the important carbonate-silicate cycle.
     In a " normal" state of affairs, carbon dioxide in the atmosphere combines with water to produce carbonic acid. This carbonic acid falls as rainwater and breaks down continental rock -- a major feature of weathering. Bicarbonate ions, HC03(-), created by the chemical weathering, wash down the streams and into the oceans. In the sea, these ions reach saturation and precipitate from the ocean as carbonate ions, CO3(2-), and accumulate in vast seafloor deposits, or are used by some animals to create hard shells.
     Once converted to rock, the carbon atoms cannot escape, except by subduction. As the seafloor is pushed underneath the world's numerous lithospheric plates, heating eventually releases the carbon as a gas again, which finds its way back into the world's atmosphere via volcanoes and sea-floor spreading margins, where the cycle starts anew . . .
     Except when subduction and volcanism fail, as with modern Epona, dropping carbon dioxide production to bare minimum as outgassing fades away. Lose one tie in a loop, and the entire system crashes, so to speak. No more CO2 for Epona. What's in a Broken Tectonic Cycle
     All the world's carbon dioxide will be lost when tectonism fails. How does this effect life? Very simply, and very profoundly. The carbon dioxide in the atmosphere provides Epona a buffer against a changing amount of sunlight from Taranis. See it this way: As a main sequence star ages, it becomes brighter. So, early out, Epona received less sunlight from Taranis than at present. With less Taranan flux, Epona should have been frozen, right? Nope.
     The amount of carbon dioxide taken from the atmosphere depends on the amount of water that is being evaporated from the seas, because one needs water to make carbonic acid. An early Epona receiving less sunlight will have less evaporation, which means less rainfall. Less rainfall means more CO2 molecules left in the atmosphere and we all know what more CO2 means: greenhouse effect. A good quantity of CO2 equals a warm and equitable habitat for life. As Taranis grew brighter with time, the amount of evaporation on Epona increased, making more rainfall and taking greater quantities of CO2 from Epona's atmosphere. With less greenhouse effect over time, the climate maintained fairly even in temperature -- until a few aeons ago.
     Without tectonism, the production of carbon dioxide falls below absorption rates, and in a few tens of million of years, much of the available CO2 becomes chemically bound to Epona's crust. Freeze time.
     At the beginning of the new low carbon dioxide era for Epona, some 1.7 billion years ago, her previously equitable climate eroded into the cold clasp of a prolonged ice age -- despite Taranis's increasing luminosity. For the terrestrial biosphere, and a little less so the aquan realm, the sustained ice age proved a significant challenge, causing vast extinctions. The very limited CO2 during this period was not enough to sustain photosynthesis very well for terrestrial plants, and they died. Herbivores quickly followed the vegetation's death march, and the carnivores subsequently suffered. In the oceans, photosynthetic organisms were able to survive by using bicarbonate as their carbon source, sustaining an aquan biome, albeit a cold one. A New Geologic Cycle Begun
     Epona's internal heat has not completely dissipated. Enough warmth has remained to produce residual bouts of terminal volcanism every one hundred million years or so, give or take an epoch or two. These huge plagues of eruptive activity release vast quantities of CO2 back into the atmosphere, providing a new greenhouse effect and an initially abundant carbon source for photosynthesizing life.
     Under this warming trend, the ice retreats, and land areas previously covered in glacial ice become exposed for repatriation by life. The volcanism spike is short-lived, say a few million years, and the warm periods only last ten to twenty million years. Long enough for terrestrial life to radiate and become established, only to be choked from the continents as the CO2 steadily drops, allowing Epona to ice over yet again.
     Epona has experienced at least twenty of these glacial events in the last 1.7 billion years, and is at a warm-period's end right now, in our modern era. Much new aerial, terrestrial and aquan life has evolved during this most recent ten million years of equitable clime.

EPONA'S BIOLOGY
     Much is known about the Tir fo Thuinn region of Epona, an ancient, flat, tectonically dead continental craton that has been weathered by rainfall and glacial action for at least one billion years. Due to space constraints, we'll only look at the primary microfauna, megafauna and megaflora of Tir fo Thuinn. The organisms described below are a world-wide presence, so Tir fo Thuinn provides a good opportunity to show what lives among the Eponan countryside. Kingdom Archaeanimalia
     Class Silacopada      Silacopods are part of a kingdom which consists of animals that have a somewhat Earth-like morphology and physiology, called the Archaeanimalia. Nevertheless, do not let these words fool you into thinking that mammals and reptiles are running around on the surface of Epona. Quite the contrary. Though the archaeanimalia have some similarities to Earth critters, such as mineralized skeletons (internal in the case of a strange group of organisms called springcrocs and external in the silacopods) and similar musculature, there are no vertebrates, and members of the existing archaeanimalia classes are quite different from anything existing on the Earth.
    Silacopods are a class of relatively small segmented organisms ranging from ant to gazelle in size -- Epona's lighter gravity seems to be aiding the larger forms. Silacopod bodies are supported and protected by an exoskeleton of silicon dioxide, basically glass. Respirating through solid silica is difficult, so the stem species had a pair of breathing stocks, which resemble antennae, on each of its ten segments. Being structured somewhat like a centipede, the basal species also had a pair of legs attached to each segment.
     All known silacopod species have evolved from the basal centipede form and are modifications of it: usually having fused many of the segments into three significant body parts and reducing the legs to four, two on some occasions. Thus, many of the critters appear to have an inordinate amount of antennae on each major segment, when in reality, these organs aid in respiration. Modification to the numerous limbs is common, with typical products being the creation of liquid-filled spines for sensing sound waves and grasping organs like those used by some arachnids and crustaceans on the Earth.
     Silacopods have filled a variety of ecological positions throughout the terrestrial reaches of Epona, though the greatest variety of critters are found in the tropics of Tir fo Thuinn, and on an isolated chain of islands found far east of the continent's mainland, called the Chirping Chain. Interestingly, even though the silacopods appear to be filling niches similar to the insects on the Earth, none are known to have adopted flying (save for some species' young utilizing wind for transport) -- a major insect feature

Kingdom Myoskeleta
     The myophyte kingdom consists of organisms that do not possess mineralized skeletons. Instead, their bodies are supported by continuous lengths of osmotic muscle called extensile muscle rods, a combination skeleton-muscle which makes the organisms very flexible. These muscle rods can extend forward and backward, as well as twist through differential activation of muscle cells. Joints are not needed, for they can be created "on the fly" by animating the proper cell groups. The basic body plan built around the osmotic muscle skeleton consists of a barrel like midsection with five muscle-rod limbs protruding from either end. The tips of the five limbs are then further divided into three smaller digits. What can such a simple body plan accomplish? A surprising amount.
     The kingdom is broken down into two phyla, the myophyta, which consists of photosynthetic organisms that reside in plant-like niches on Epona, and the pentapoda, which has produced a host of animals highly derived from the basic body plan described above.

Phylum Myophyta
     These photosynthetic organisms, which have evolved from a tiered seaweed, have a very simple form: The previously mentioned barrel is often carried upright, like the trunk of a tree, and the five limbs on one end are sunk into the ground, like roots. At the top of the barrel, the other five limbs have evolved into a large umbrella leaf, so that a single tiered member of this phylum looks somewhat like an oversized mushroom. Five to fifteen spines, derived from the tridactyl nature of the muscle rob limbs, support the leaf, like the arms of said umbrella.
     This "plant" form, known as the pagoda tree, is not restricted to one tier. A new barrel and associated leaf can be cloned from a growth bud that exists in the center of the leaf, quickly adding another level. Growth can continue, carrying pagodas to great height. Some myophytes are capable of branching via a polyembryonic method, effectively multiple cloning, though this tends to be simple and is usually carried out in two's, three's or five's. Though the branching forms share many features with the pagodas, they are not the same, and are called neopagodas.
     There is no wood on Epona. The carbon dioxide required for the wood-making process was not available for the pagoda's tiered seaweed ancestors, and the terrestrial myophytes have maintained this ancient carbon intensive trait. Pagoda stems are held rigid by the osmotic pressure in the muscle cells. This osmotic characteristic gives the pagoda animal-like freedoms. Trunks are very mobile, and they easily track the sun. Tendrils and stems can wrap around a support while one is watching. As a storm nears, pagodas can detect the dropping atmospheric pressure, and lift their leaves up or drop them down (like skirts?!) in an effort to protect the large photosynthetic structures from high winds. A natural and striking barometer! Occasionally pagodas will shrug off an unwanted visitor, like an avian myoskeletal critter who's landed on the myophyte for a hearty meal.
     Strongly cold climes and pagodas often are usually not a successful combination. Having no bark for protection, the winters kill myophytes off by the billions, whole forests decimated by a single hard freeze. However, Epona has a very thin atmosphere, and even in the tropics at sea level the temperatures tend to drop toward freezing during the night. To combat this problem, pagodas produce various alcohols as antifreeze. Be careful with your campfires.
     Silacopods like to eat pagodas. So do myoskeletal animals. Why not? Pagodas, in most instances, can't run away. Disliking growing holes in their leaves, pagodas have established a defense routine similar to Earth flora: chemical warfare. Silacopods aren't the only reason for a poison defense, for pagodas also have each other. Carbon dioxide necessary for photosynthesis is rarefied even on modern Epona, and pagodas have very large leaves to absorb enough of the life-sustaining gas. Those dome leaves require much space. To create room, the myophytes diligently spend energy making pagodacides to keep near relatives away. Toxin differentiation is so detailed, in fact, that it is the most effective characteristic to use when identifying species, since many pagodas look quite alike morphologically.

Phylum Pentapoda
     In pentapods, the basic myoskeletal barrel contains all the vital organs, including the brain (housed in a region of collagenized [basically tendon] muscle rod), and the sensory apparatus, which consists of four eyes, two ears, and a third ear located on top of the head that serves as a sonar sender/receiver.
     The barrel also houses the respiratory organ, a chamber created by a sheath of muscle rod, forming a hoop-like structure. Two lesser rings of muscle rod sit at either end. Air enters through the mouth, and the muscles sequentially pump it into a network of self-similarly branching bronchi. Upon reaching the lowest level of branching, the alveoli, oxygen is absorbed directly into the muscle (and any aerobic organs) from the airstream. At the same level, carbon dioxide and water are expelled, being carried through a number of tributary paths before being "exhaled" from pores in the skin.
     Reproduction is achieved by an exchange of spoor through the mouths of two individuals. Being parthenogenic, both participants will get pregnant (no gender roles here). The embryos develop in a budding zone at the back of the single respiratory pump, and birthing is achieved by coughing up the newborn before it becomes too large and obstructs breathing.
     The pentapod phylum has produced at least two well-known major groups on Epona, the ceretridons and avians. In a several million year radiation similar to the Earth's Paleocene, both groups have diversified significantly in the past ten million years, and contain many species.

Class Ceretridonta
     The pentapod's simple form has been modified significantly in the ceretridons. The barrel has elongated and grown larger, housing a massive digestive system (especially for the herbivores), and has become fenestrated to reduce weight. Thus the barrel looks ribbed. A head-like structure exists at the front end of the barrel, though it houses only the sensory organs -- the brain is still deep within the original barrel. The sonar ear is practically nonexistent, for it has atrophied in favor of eyesight. All ceretridons utilize their four eyes, with many having a pair aimed forward for binocular vision and a pair aimed upward to spot aerial predators. At the front of the head is a simple mouth that has four to twelve conical, chitinous teeth and a single tongue. The teeth represent the finger terminations on what would otherwise be four of the standard five pentapod arms originating from the front of the barrel. The tongue is the fifth limb. Five other limbs originate from the back end of the barrel. Two arms are carried forward, often inside the body, so that they protrude from the sides of the head, and are used for grasping. The other three limbs trail behind and are the animal's legs, hence the "tridon" in ceretridon. However, there are thousands of species of ceretridontid, and many locomotory patterns have evolved among them: monopedal, bipedal, tripedal, and even quadrupedal and pentapedal (using the RarmsS by the head). The class has also produced herbivores (actually pagodivores), carnivores, scavengers and parasites along with the different leg numbers.
     Pagodivorous ceretridons have to tolerate many toxins in their lives. Most ceretridons, in fact, are only capable of consuming one, or a few, toxins, so the pagodivores tend to be quite specialized, seeking a specific type of pagoda, usually identifying it through taste. Many pagoda eaters store the toxins they consume as a defense against predators, wearing garish colors and patterns as a warning to any lurking carnivores. With their toxin defense, most pagodivores are solitary, or form very small groups. However, a number of migratory herding species do exist in the temperate climes, where their food pagodas die back into the warm temperate reaches every winter.
     Because of their prey's inherent toxicity, many carnivores also tend to specialize, feeding solely on one, or a few species of pagodivores. What rolls down hill? Carnivores also tend to be brightly colored and patterned, features for mate selection not too unusual for an animal group with exceptional eyesight. Some carnivores have all four eyes facing forward, establishing a very acute depth perception in combination with their color vision. Carnivore mouthpart limbs tend to be very specialized, many having chitinous talons on their fingertips, an aid in prey acquisition.
     Silacivorous ceretridontids face similar toxin problems, for the silacopods use pagoda toxins for defense. These small ceretridons have the largest teeth, relative to body size, among their kind, a requirement for crushing the hard siliceous shells of their food. The teeth wear down quickly, and are perennially growing to compensate for the loss of material.

Class Aviana
     Avians are similar to the ceretridons in construction, save for a few important aspects. Two of the three standard ceretridon legs have elongated into wings that sit near the head of the critter, while the remaining leg has grown very large, lengthening its three fingers to support another (two-part) broad wing, one that is larger than the other two lifting members. The middle "finger" stretches through the fluke of this large hind wing and becomes a tail. The tail effectively pulls the beast's center of mass rearward, putting it at the center of lift located in the region of the massive rear wing. A triangular sonar RearS sits ahead of the eyes on top of the "cranium". Sonar is the avian's primary sense, though their eyesight also is good. Eyes in avians are often located on the side of the head, giving the creature a 360 degree field of view. Usually the other pair of optical sensors are highly atrophied.
     Propulsion is achieved through flapping the two forewings, and lift is generated by the broad hind fluke. This is an effective combination, capable of carrying the animal forward at speeds similar to light aircraft.
     Many avians have assumed the roll of predator, pouncing upon ceretridons, and snatching each other from the sky. There are large predators with wingspans over ten meters that hunt solely by sonar, having atrophied eyesight. Such predators tend to feed on mid-sized avians, as well as many of the ceretridontids -- avians have developed organs that the ceretridons don't have, and can tolerate a broader range of toxins than their terrestrial brethren. Other predators are small, like sparrows, and flock, attacking prey en mass like Earth's piranha. Pagodivorous avians abound, laying flat on tasty umbrella leaves with their wings outstretched, and camouflaged in detail to hide from sight predators.
     The avians have produced Epona's sophont, the Uther. The uthers were originally scavengers, flying in widely separated groups to aid each other in finding the rare corpse on the ground. Having weak teeth, Uthers eventually created tools in order to process food easily. With sharp tools, hunting followed, and a new lifestyle that led to civilization.

IN CONCLUSION
     The paragraphs above summarize only a few aspects of Epona, a tiny glimpse at a world that is very complex and detailed. Fortunately, for those who are interested in seeing more of Epona, there's an effort to depict the planet in its own publication(s). Epona is no longer restricted to Contact; in 1995, the participants of Epona's creation have established a partnership called WorldBuilders that continues the development of Epona, and is pursuing many paths to give the world a visible spot in the science fiction genre.