### Sterile Worlds (Solid) **Overview** Sterile worlds are dead worlds. Sterile worlds are representative of a large share of the worlds in the universe and a stark reminder of how the universe wasn’t made for us. You find these in every system, often with useful resources or a useful position to control in the star system. Sterile worlds are meteorologically and geologically dead places. No life of any complexity can develop on a sterile world. **Examples** The moon, Ceres, the various Kuiper belt objects, Io, Callisto and Mercury are all considered sterile worlds as are most of the moon around Uranus. Sterile worlds do not mean moon-like, even if a fair share of these worlds have features in common with the moon. **Geology** Geological activity is limited to tidal heating on sterile worlds, to the point where asteroid impacts shape the terrain on these worlds more than anything else, creating landscapes of lava basins and craters. In cases, such as Io, volcanism may be a prevalent force, but never make a desert world due to the weak gravity. Sterile worlds that have had massive asteroid impacts will have massive cliffs and jagged peaks. Resources on sterile worlds are usually concentrated into craters and lava tubes. Icy sterile worlds do not even have subglacial oceans, instead such worlds have a warmer, slushier ice layer between the crust and core. Sterile worlds do have some activity, especially if there is some tidal activity from their core. Such activity is however limited to earthquakes or sink holes. **Meteorology** Sterile worlds always have very tenuous atmospheres, sometimes they may have weak gusts of wind, but no systems prevalent enough to make much a difference. Sterile worlds are either too small to have an atmosphere or too dead to regenerate an atmosphere after a cataclysmic impact. Any atmosphere building from volcanoes is lost thanks to the weak gravity sterile worlds always have (if said world could collect an atmosphere from volcanic ash, it’d be desert world). **Life** Sterile worlds almost never have life, hence their namesake. This is the case for worlds that always were sterile, anyhow. Occasionally sterile worlds may have endolithic life surviving deep below the surface subsiding on chemical energy in cases where life developed before the world died out. ### Desert Worlds (Solid, Gas) **Overview** Desert worlds are a common planet type in the galaxy. Lacking much liquid, but still amazingly flexible, these dynamic worlds will prove to be incredibly hostile or a goldmine of life. You never know. Desert worlds may have numerous seas, but no oceans. Desert worlds include icy worlds with an atmosphere, so Titan is considered a desert world in this classification system. **Examples** Mars, Venus and Titan are all desert worlds, showing just a taste of the variation desert worlds can have. Pluto is a borderline case due to the seasonal atmosphere it has. **Geology** Desert worlds tend to have volcanism when they are bigger or when they are young. Smaller desert worlds usually die geologically long before the sun goes supernova, with their core too cold to sustain convection. Larger desert worlds can sustain for much longer. Volcanism is a frequent feature on desert worlds. Desert worlds tend to be mineral rich compared to Terran worlds, with all sorts of exotic materials found in the ancient hillsides. **Meteorology** Weather on desert worlds tends to be very erratic, with the large swings of temperature that permeate these worlds and their lack of oceans to mediate the temperature. Desert world climates are much more radical in their shifts, and weather patterns will change at the turn of a dime by the season. This can vary highly depending on the atmosphere, of course. One should expect a runaway greenhouse on desert worlds with a thick atmosphere to take hold, especially a carbon rich one made by volcanic activity. **Life** Life on desert worlds is significantly less common than that on Terrans. This is balanced out by how frequent desert worlds occur in the universe, to the point where you still will be more likely to find a desert world with life than a Terran world with life. Life on Deserts worlds will have endured far, far more desolate conditions than anything seen on [[Earth]] thanks to the massive temperature swings desert worlds endure. There are cases of biospheres where many of the native fauna borrow and hide during both day and night and only move around on the surface during dawn and dusk. Large underground ecosystems are a common feature, as is life that is highly seasonal in nature. Life sometimes acts as a stabilizing force on desert worlds, regulating the temperature in place of water, but this is not a given. ### Terran Worlds (Solid, Liquid, Gas) **Overview** Terran worlds are worlds with ocean and land. Terran worlds do not mean worlds like Earth, all matter of liquids may permeate such worlds. Still, Terrans have the most chemical complexity of worlds and are most likely to give rise to complex life of all the world types listed. **Examples** Earth is the only known Terran world thus far. **Geology** Terran worlds will almost always have systems of tectonic plates. These plates will move the continents around, make mountains, cause waves of volcanic activity, earthquakes and make landslides. Terran worlds have a very diverse store of minerals, with mountainous regions being more mineral rich for instance. Terran worlds have much less craters due to the geological activity that regularly occurs on them, limiting the degree which asteroid impacts shape the surface of the planet. **Meteorology** Terran worlds always come with advanced weather systems where hurricanes, tornados and rain storms are common occurrences. Wind cell systems exist frequently and the temperature distribution is highly seasonal. Terran temperature systems are regulated by the oceans, giving them more stable systems than desert worlds. However, some Terran worlds out there are known to have amazingly violent weather systems from the sheer stacking of factors like the arrangement of oceans and mountains, the density of the atmosphere, seasonal variations and so on. **Life** Life on Terran worlds tends to get rather complex should oxygen producing life ever dominate. Terran worlds are very diverse places and their stability allows for rather expansive biospheres to develop in many different conditions. The less erratic temperatures mean life is openly on the surface on a Terran worlds with only seasonal variations to worry about. Terran worlds can develop much more biomass than most of the other world types here except for certain kinds of Oceanic worlds. ### Oceanic Worlds (Liquid, Gas) **Overview** Oceanic worlds have global oceans with hardly any land or no land at all. They tend to have thick atmospheres of water vapor. Oceanic worlds range from super-earths with a couple tiny volcanic islands at the peak of massive underwater mountains to sub-Jovian worlds with oceans so deep you get pressurized ice. Oceanic worlds may be of any liquid, provided it spans the whole world. **Examples** No oceanic worlds exist in our solar system, but there are various exoplanets suspected of being water worlds out there. No concrete **Examples** however. **Geology** Most oceanic worlds have underwater mountains and geothermal vents, except for the ocean worlds whose oceans are too deep to have a stony sea floor (as you get a pressurized ice layer instead). This is because oceanic worlds tend to be massive worlds as well, so you get active cores and tectonic plates. Smaller ocean worlds tend to freeze too soon or lose their atmosphere due to lacking the gravity to retain the water-vapor atmosphere. **Meteorology** Without any land, winds on a water world have no mountains in the way, which means you get wind systems that regulate the temperature depending on the latitude you are at much more than on a Terran or desert world. This means you would get incredibly stormy regions and incredibly calm regions. You also would get very cold poles, which means ice caps are a significant possibility on an ocean planet. However, the temperature of the planet remains highly homogenous due to the global ocean absorbing and retaining much of the heat from the local star. **Life** Life on ocean planets is very plausible if there are geothermal vents to cook up the primitive forms of life an ocean world would need. The depths of an ocean world do not stop life from getting complex as you get life drifting to the surface to absorb sunlight remarkably fast. Life on ocean worlds would be distributed by latitude and would see aquatic life distribute itself all over the planet due to the highly stable temperature distribution which ocean planets tend to have. Evolutionary pressures would still exist from other life forms. A stable planet doesn’t always mean a stable biosphere. ### Subglacial Worlds (Solid, Liquid) **Overview** Subglacial worlds are worlds covered by a global ice sheet with an oceanic mantle. Subglacial worlds are usually supported by tidal heating. Subglacial worlds are a very common type of world, often in orbit of other worlds and always a potential place for life to occur. You don’t know until you drill inside. To qualify as a subglacial world, you can’t have an atmosphere. This means sub-glacial worlds are usually tiny compared to Earth. **Examples** Europa and Enceladus are the poster children for subglacial worlds, as are Charon, Triton and Titania. **Geology** Subglacial worlds are much like ocean worlds in their geology underwater, except that their underwater terrain is oriented around hotspots instead of on tectonic plates as subglacial worlds are heated by tidal forces. For that reason, subglacials are usually in binary systems or moon systems. Cryovolcanic activity is a common feature of subglacial worlds with thin ice sheets. The global glacier is molded by the ocean below it much as crust of other world types are molded by the mantle below. **Meteorology** What atmosphere a subglacial world might have had from cryovolcanic activity is lost to space due to the weak gravity. Larger worlds with global ice cover with an atmosphere are considered desert worlds instead. It does rain on subglacial worlds thanks to the cyrovolcanos. **Life** Life inside subglacial worlds would need an oxygen rich environment, which is possible thanks to the geothermal vents subglacial worlds usually have. Without any sunlight, life would be entirely reliant on tidal heat and pent up energy from minerals from the stony core of their world. Such abyssal ecosystems would extend itself to the subglacial sheet itself even despite how cold the liquid gets, as there is all matter of detritus to thrive on. However, most activity would be limited to near the core, especially in cases of complex life. ### Jovian Worlds (Gas) **Overview** Jovian planets are the largest class of planets, being made primarily of gas and pressurized gas. Ice giants and gas giants despite the huge differences in size are part of the same class due to both being gas dominant worlds. Jovian worlds are a common fixture of star systems and often host a moon system with more worlds. **Examples** In our own sol, you have Jupiter, Saturn, Uranus and Neptune as jovian planets. **Geology** There are no geological processes on Jovian planets, there is no land at all. You just get a pressurized sea of liquid hydrogen when you go deep enough. **Meteorology** Jovian worlds consist of large convection cells with massive stacked clouds thanks to the internal heating. Jovian worlds have cloud layers with different substances in each layer and with no land at all, wind velocities are far faster than what you typically find on smaller terrestrial worlds. Jovian weather systems are much more expansive as well, with hurricanes the size of planets being a common feature. **Life** Jovian worlds as incredible as it sounds, can at times have life. Life on Jovian worlds would be the product of metallic seas and kinetic energy. Such life would rely on electricity for metabolism, such as that from the massive storms which rage on the world and would have to be able to survive a high range of pressures and atmospheric conditions, which the downwards and upwards currents would subject any life on a Jovian world to.