Mercury, with small bodies, high densities and cannot escape, except by subduction. As the little in the way of atmospheres. The large seafloor is pushed underneath the world’s chunks of rock are tidally locked to Taranis, and numerous lithospheric plates, heating eventually Grannos' long ago atmosphere has been frozen releases the carbon as a gas again, which finds into carbon dioxide ice on its night side. Epona its way back into the world’s atmosphere via follows, with a mass of 0.55 Earth's, an oxygen- volcanoes and sea-floor spreading margins, ated atmosphere that averages 0.577 bar at the where the cycle starts anew . surface, continents of silicate rock, temperate Except when subduction and volcanism fail, climate and seas of water. The fourth world, as with modern Epona, dropping carbon dioxide Sucellus, with a high density of 6.4 and mass of production to bare minimum as outgassing ceas- 2.0 is a sizable terrestrial world covered in a es. Lose one tie in a loop, and the entire system deep ocean and insulated by a carbon dioxide crashes, so to speak. No more CO2 for Epona. atmosphere of roughly four bars. The next four planets are a family of gaseous What's in a Broken Tectonic Cycle giants, with huge masses, from 5.9 to 206 Earth's, and light densities, all sitting around 0.7- All the world’s carbon dioxide will be lost 2.4 g/cm3. The fifth world, Rosmerta, is the when tectonism fails. How does this effect life? smallest of the family, a mini gas giant with a Very simply, and very profoundly. The carbon viciously hot world-encircling ocean being sus- dioxide in the atmosphere provides Epona a buf- tained under an equally challenging atmosphere fer against a changing amount of sunlight from that exceeds 1,000 bars in pressure. The small Taranis. See it this way: As a main sequence gas giant is followed by the largest, Borvo. star ages, it becomes brighter. So, early out, Borvo is 65% the mass of Jupiter and is similar Epona received less sunlight from Taranis than in nature, producing a powerful magnetic field, at present. With less Taranan flux, Epona should tightly holding a vast array of moons and pre- have been frozen, right? Nope. senting a surface of seething storms. Bormo, The amount of carbon dioxide taken from world number seven, is similar to Uranus, even the atmosphere depends on the amount of water possessing a strong axial inclination of 73 that is being evaporated from the seas, because degrees. Bormanus, the eighth planet from one needs water to make carbonic acid. An Taranis, is similar to Saturn in density and mass. early Epona receiving less sunlight will have This icy-ringed world follows the most elliptical less evaporation, which means less rainfall. path of Epona’s sister planets, maintaining a Less rainfall means more CO2 molecules left in mean eccentricity of 0.16. the atmosphere and we all know what more CO2 The final world, Sirona, is Tritonian, being means: greenhouse effect. A good quantity of developed for the uther, the start of culture was comprised of ices, though it is more massive A BRIEF HISTORY OF THE CO2 equals a warm and equitable habitat for developed, land areas were defined and semi-ex- than Mars. Occasional cryovulcanism maintains life. As Taranis grew brighter with time, the EPONA PROJECT plored, climate zones were created, as was the a thin atmosphere of nitrogen, methane and amount of evaporation on Epona increased, uther’s language. Many new and exciting plants hydrogen. making more rainfall and taking greater quanti- The COTI Mundi Project Epona came about and animals were created, as was much art work, ties of CO2 from Epona’s atmosphere. With less because two people had the belief that the usual including examples of Eponan artifacts. EPONA’S GEOLOGY greenhouse effect over time, the climate main- COTI (cultures of the imagination) Projects from At Contact XII the COTI Mundi project was tained fairly even in temperature--until a few the Contact Conferences could be better. The renamed The Epona Project, and the highly eons ago. usual COTI session was a three day frenzy in detailed world was presented to the rest of the Kill tectonism, and the production of carbon which two teams each created worlds and Contact group. Many people were very dioxide entirely. In a few tens of million of brought them together for a "first contact" on the impressed by what had been done by these dedi- years, much of the available CO2 becomes third day. Dirk van der Elst thought that three cated people. One of those impressed was SF chemically bound to Epona’s crust. Freeze time. years was a better time frame for this project, writer Larry Niven. He wrote, “I have not seen a At the beginning of the new low carbon and Martyn Fogg was asked to create a fresh playground of this size.” It was at this time that dioxide era for Epona, some 1.7 billion years new planet for people to build on. the Epona team members created the partnership ago, her previously equitable climate eroded into Martyn and his cohorts in Great Britain went called WorldBuilders. the cold clasp of a prolonged ice age--despite one better and produced an entire planetary sys- In the past year WorldBuilders team mem- Taranis's increasing luminosity. For the land- tem. The third planet, though a life-bearing bers have produced more art work, fleshed out based biomes, and a little less so the aquatic world, is nothing like Earth. It is a planet that is more of the culture and have sold one story and realm, the sustained ice age proved a significant becoming senescent, and which can only support one fact article relating to Epona to Analog challenge, causing vast extinctions. The very intermittent habitability. The land is only equita- Science Fiction and Fact magazine (due out in Epona accreted a similar distance from limited CO2 during this period was not enough ble for life during 10 million years in every 100 the November 1996 issue). Taranis as the Earth did the Sun, so the composi- to sustain photosynthesis very well for terrestrial million. When this happens a rapid and dramatic For a more detailed account of the history of tion between the two worlds is quite alike. plants, and they died. Herbivores quickly fol- adaptive radiation of sea and shore dwelling Epona, please read the work published in the Epona has a lower abundance of heavy ele- lowed the vegetation’s death march, and the car- organisms sweep the planet. When the life-sup- binders available else where in this display. ments, accounting for a lower density. During nivores subsequently suffered. In the oceans, porting cycle fails, and gaseous carbon dioxide the first 3.3 billion years of existence, Epona photosynthetic organisms were able to survive becomes depleted, a mass extinction driven by THE PLANET EPONA possessed a liquid iron-nickel core, a convective by using bicarbonate as their carbon source, sus- the failure of planetary homeostasis drives mantle and shifting lithospheric plates. taining an aquatic biome, albeit a cold one. advanced life back into the equatorial seas. Epona's tectonic activity did not last as long The planet was given to the group of adven- as it has on the Earth. Being a smaller world, A New Geologic Cycle Begun turers at Contact X at the end of the 19th cycle, Epona has a higher surface to volume ratio than just as an ice age was ending. This group of the Earth, and thus has had its store of internal Epona’s internal heat has not completely dis- people produced two promising creatures, the heat dissipated at a significantly faster rate. sipated. Enough warmth has remained to pro- "ceretridon" and the "springcroc" along with Nearly two billion years ago, Epona’s tectonism duce residual bouts of terminal volcanism every details of their evolution. Other life-forms and began to slow, and later froze up completely as one hundred million years or so, give or take an conditions were also created, but not in as much the lithosphere continued thickening. Many epoch or two. These huge plagues of eruptive detail. The planet was also fleshed out with cli- types of mountain building stopped, and conti- activity release vast quantities of CO back into matic and geomorphological changes that would 2 nental masses simply weathered and eroded the atmosphere, providing a new greenhouse occur as it emerged from 100 million years of away. effect and an initially abundant carbon source ice age. During the first year people continued for photosynthesizing life. to think about the world and prepare to meet Habitability: Maintained by a Cycle Under this warming trend, the ice retreats, again for Contact XI. Greg Barr and Martyn The following text is an excerpt from an article, and land areas previously covered in glacial ice Fogg produced a newsletter that went out to all titled Epona, published in the November 1996 Highly weathered continents are okay as far become exposed for repatriation by life. The interested parties, keeping everyone up to date issue of Analog. as Epona’s biome is concerned, but breakdown volcanism spike is short-lived, say a few million on the work that had been done and what was of tectonism has one major side effect for life. years, and the warm periods only last ten to continuing to be done. People from all over the Epona’s Family of Worlds Epona’s dead geology severs the important car- twenty million years.