Not to be confused with Tethys the moon of Saturn. Tethys the planet is a Qohathoth world located in Ursa Minor.
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The Pherkad System
The Pherkad System. Sizes are not even slightly to scale.
The system around Pherkad ( also called Gamma Ursae Minoris, ) an A-type star about 480 light years from Earth. There are four planets: Sangarius, Tethys, Oceanus, and Proteus – the inner two are rocky, the two outer are gas giants.
Sangarius has one moon, Tethys two, Oceanus six, and Proteus four. With the exception of Tethys' moons, the other moons are named things like 'Oceanus Alpha' and 'Oceanus Beta', and down through decreasing size.
General Physical Environment
Tethys is slightly smaller than Earth with similar gravity. The air is close enough to Earth-normal not to matter, the surface is 88% water, counting ice as 'land' ( to be an official water planet, the surface must be at least 90% water. ) Its orbit is farther from its sun than Earth – the most habitable section is around the equator, where the temperatures tend to be between ten and twenty degrees Celsius year round. The orbit is about that of Mars, the Tethyn year is equivalent of 674 Earth days. The days are twenty-two hours long. While not a true water planet, it is very damp. There are two rainy seasons, one longer than the other.
There are two land masses designated continents – Ki and An. Ki covers about eighteen million square kilometres and is the continent that homes the entomorph hive and Port Tethys. An is the north polar land mass and covers about twenty-one million square kilometres. The ice cap on the south pole covers another fifteen million and the scattered islands add up to another ten million.
Tethys is generally thought to have no tropical zone because Ki, which is on the equator, is temperate. This is incorrect.
Tethys is one of the worlds terraformed by the Qohathoth. As such, it's not as biodiverse as a natural world would be. Geological data says that Tethys used to be an ice world out beyond the orbit of Proteus, but the Qohathoth moved it. It had been warmer earlier in its new life as a terraformed world, but something happened two million years ago that changed the environment slightly, making the place cooler than it had been.
Geographic and biological data show that Tethys had been a warmer planet overall, but some major event happened that caused the planet to drastically change its climate.
Entomorph mythology references a fire from the sky, and geologic data backs up that there was an impact in the Dagon Ocean nearly two million years ago - either a large asteroid or a third moon that fell out of orbit. The resulting change in the ocean floor changed the currents. Now polar currents sweep past Ki, cooling it despite being on the equator.
As all animal life on Tethys is cold-blooded, adaptation took place on Ki to combat the cold. In the fish and reptiles, the result was vastly increased size. In the insects, the result was increased size and vastly increased intelligence. It is thought that this was the nudge the proto-entomorphs needed to develop sapience.
The amphibian life of Ki could not adapt and died out. Amphibian life still exists elsewhere on the planet.
The continent of Ki and surrounding islands.
Tethys' only inhabited continent, parked on the equator and spreading north, flanked by the Cthulhu and Dagon Oceans. The continent includes Enlil.
While Tethys lacks true mountains, the terrain gets hillier and higher as one heads west. It is also generally warmer in the west than the east.
The land is heavily forested - a mix of temperate and temperate rainforest. The forests thin as one heads north, until it shades into tundra. Snow is only known on the northern parts of the continent.
The major currents affecting the southeast coast of Ki.
The climate and marine ecology of Ki is heavily influenced by ocean currents. Despite being on the equator, cold currents from the north and south poles chill the water to the south and east of Ki, cooling the land.
The polar currents also contribute to the marine ecology by carrying nutrients to the shallower waters of the Sons of Tiamat and Dagon's Gate island chains. The combination of transported nutrients, nutrients that slough off the islands, and shallow water that allows sunlight to produce algae and sea plants creates an extremely rich marine environment capable of supporting a host of large predators.
The inhabited section of Ki.
The Inhabited Zone
Port Tethys is located on Ki's eastern coast, on the Bay of Tiamat. The land alotted to humanity is an area of approximately ten kilometres square. There are fewer restrictions on the water - the only restrictions on fishing are to keep the environmental impact minimal. As well, humanity is allowed to leave the reservation for various purposes, provided they stay out of the entomorphs' no trespassing zone.
The entomorph hive is approximately two-hundred kilometres inland. Little is known of it beyond that it's underground and entomorphs live there. The term 'entomorph territory' refers to the lands they actually use - of course, the entire planet belongs to them.
The no trespassing zone is to protect the entomorphs' privacy. While their territory covers far more area than the zone, the zone keeps the humanoids away from the hive. Being nearly a hundred kilometres from Port Tethys, it's rare for a human or Aquaan to stray so far. Humanoids caught in the no trespassing zone are shown back out.
The Nyarlathotep Islands
The long island chain that marks one border between the Cthulhu and Dagon Oceans.
The currents that flow around the Islands are warm, drawn from the equatorial oceans rather than swept down from the poles. However, the weather is turbulent. Hurricanes and other storms wrack the Nyarlathotep and Ugallu Islands, rendering them unsafe for colonisation.
Only a cursory exploration has been made of the island chain, which is unfortunate since the brief surveys indicate that the life there was less affected by the climate change of the Cateclysm. A more thorough study of the Islands might yield clues to the world Tethys was seeded from.
While more adapted to cold than heat, the entomorphs are limited even on Ki - they can't handle snow and the northern reaches of the continent are too cold for them. They never managed to colonise beyond Ki. Given the state of the rest of the planet, there's very little land away from Ki that they could live on even if they could get there.
A strong flier might be able to reach Enlil by a series of island-hops. However, this was never discovered.
For a planet that is both inhabited by native sapients and has been known to humanity for two and a half centuries, Tethys remains largely unexplored. The entomorphs never left Ki, and between the bad weather and courtesy to the entomorphs, humanity never had more than a cursory look-around. More so underwater - the Sea of Tiamat has been explored with some thoroughness, but little further.