Hemisu
 Hemisu's supercontinent as seen from space. | |
| Orbital characteristics | |
|---|---|
| 149598023 km (92955902 mi; 1.00000102 AU) | |
| Eccentricity | 0.0167086 |
| 224.701 d (0.61520 yr) | |
| Satellite of | Hoku |
| Physical characteristics | |
Mean radius | 6371.0 km (3958.8 mi) |
| 510072000 km2 (196940000 sq mi) | |
| Volume | 1.08321×1012 km3 (2.59876×1011 cu mi) |
| Mass | 5.97237×1024 kg (1.31668×1025 lb) |
Mean density | 5.514 g/cm3 (0.1992 lb/cu in) |
| 9.807 m/s2 (1 g; 32.18 ft/s2) | |
| 11.186 km/s (40270 km/h; 25020 mph) | |
| 23.4392811° | |
| Atmosphere | |
Surface pressure | 1 atm (100 kPa) |
Hemisu is a terrestrial planet located in the Outer Band of the Talin Galaxy. It orbits the orange dwarf star, Hoku. It has three small moons that orbit it. Hemisu offers many biomes such as plains, forests, savannahs, deserts, barren mountains/plateaus, and a vast freshwater ocean. It is comprised of one massive supercontinent and superocean, with one side of the planet being almost entirely land and the other water, with a few major cities and spaceports. It is home to a multitude of animals and plant life. The sentient native species are the Nemeans, lion-like humanoids named after the Nemean lion from Constantian mythology. The planet and its moons are also home to a sizable population of humans, who first settled there in 356 BHT.
Hemisu and its moons are rich in a rare metal ore called etherium that when refined is used in almost everything by the humans that mine it. As such, the surface of Hemisu and its moons are covered in mines and drilling facilities. Due to the many practical uses of refined etherium, it is the most lucrative trade commodity on the planet, and as such is heavily regulated and protected.
Etymology
Hemisu, from the Constanti “hēmisys”, which translates to “half” (temporal and spatial). The humans that settled here named it in reference to Plato’s use of the word for half ἥμισυ (hemisu) much as English refers to one's other half as a partner, but instead referring to the two halves of the planet being a supercontinent and superocean.
Physical characteristics
Size and shape
Hemisu has a rounded shape, through hydrostatic equilibrium, with an average diameter of 12,742 kilometres (7,918 mi), making it the largest planetary sized and largest terrestrial object of the Hoku Solar System, as it is the only planet orbiting Hoku.
Due to Hemisu's rotation it has the shape of an ellipsoid, bulging at its Equator; its diameter is 43 kilometres (27 mi) longer there than at its poles. Hemisu's shape also has local topographic variations. Parallel to the rigid land topography the ocean exhibits a more dynamic topography.
Internal structure
Hemisu's surface is the boundary between the atmosphere, and the solid earth and ocean. Defined in this way, it has an area of about 510 million km2 (197 million sq mi). Hemisu can be divided into two hemispheres: by latitude into the polar Northern and Southern hemispheres; or by longitude into the continental Eastern and Western hemispheres.
Hemisu's ocean covers 47%, or 121,703,421.31 km2 (75,623,000 sq mi) of Hemisu's surface. This vast pool of freshwater is known as the Great Ocean, and makes Hemisu with its dynamic hydrosphere a water world or ocean world. Indeed, in Hemisu's early history the ocean may have covered it completely. The ocean covers Hemisu's oceanic crust, with the shelf seas covering the shelves of the continental crust to a lesser extent. The oceanic crust forms large oceanic basins with features like abyssal plains, seamounts, submarine volcanoes, oceanic trenches, submarine canyons, oceanic plateaus, and a globe-spanning mid-ocean ridge system.
Just over half of Hemisu's surface is land: 53% or 167,946,311.808 km2 (104,357,000 sq mi). The land surface includes many islands around the globe, but most of the land surface is taken by the supercontinental landmass. The terrain of the land surface varies greatly and consists of mountains, deserts, plains, plateaus, and other landforms.
Land can be covered by surface water, snow, ice, artificial structures or vegetation. Most of Hemisu's land hosts vegetation.
The pedosphere is the outermost layer of Hemisu's land surface and is composed of soil and subject to soil formation processes. Soil is crucial for land to be arable. Hemisu's total arable land is 10.7% of the land surface, with 3.3% being permanent cropland. Hemisu has an estimated 16.7 million km2 (6.4 million sq mi) of cropland and 33.5 million km2 (12.9 million sq mi) of pastureland.
The land surface and the ocean floor form the top of Hemisu's crust, which together with parts of the upper mantle form Hemisu's lithosphere. Hemisu's crust may be divided into oceanic and continental crust. Beneath the ocean-floor sediments, the oceanic crust is predominantly basaltic, while the continental crust may include lower density materials such as granite, sediments and metamorphic rocks, as well as an abundance of etherium. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the mass of the crust.
Hemisu's surface topography comprises both the topography of the ocean surface, and the shape of Hemisu's land surface. The submarine terrain of the ocean floor has an average bathymetric depth of 6 km, and is as varied as the terrain above sea level. Hemisu's surface is continually being shaped by internal plate tectonic processes including earthquakes and volcanism; by weathering and erosion driven by ice, water, wind and temperature; and by biological processes including the growth and decomposition of biomass into soil.
Satellite system
The three moons of Hemisu are Ether 1, 2, and 3, named due to the abundance of etherium ore on all three. They are irregular in shape and relatively small. Ether 1 is the largest. Its mass is 1.2% that of the Hemisu, and its diameter is 3,474 km (2,159 mi), roughly one-quarter of Hemisu's. Ether 1 orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Hemisu. Tidal forces between Hemisu and Ether 1 have synchronized the its orbital period (lunar month) with its rotation period (lunar day) at 29.5 Hemisu days, causing the same side of Ether 1 to always face Hemisu. Ether 1's gravitational pull—and, to a lesser extent, Hoku's—are the main drivers of Hemisu's tides. Compared to Ether 1, Ether 2 and 3 are significantly smaller than Ether 1; Ether 2 has a diameter of 22.2 km (13.8 mi) and a mass of 1.08×1016 kg, while Deimos measures 12.6 km (7.8 mi) across, with a mass of 1.5×1015 kg. They both orbit around one another while also orbiting around Hemisu. Ether 2 orbits with a semi-major axis of 9,377 km (5,827 mi) and an orbital period of 7.66 hours; while Ether 3 orbits farther with a semi-major axis of 23,460 km (14,580 mi) and an orbital period of 30.35 hours.
Two major hypotheses have emerged as to the origin of the moons: The first suggests that they originated from Hemisu itself, perhaps from a giant impact event. The second suggests that the two smaller moons are captured asteroids. Both hypotheses are compatible with current data, though upcoming sample return missions may be able to distinguish which hypothesis is correct.
Atmosphere
The atmospheric pressure at Hemisu's sea level averages 101.325 kPa (14.696 psi), with a scale height of about 8.5 km (5.3 mi). A dry atmosphere is composed of 56.084% nitrogen, 18.946% oxygen, 10.013% carbon dioxide, 10.934% argon, and trace amounts of other gaseous molecules. Due to the oxygen being less than 19.5% and an increased amount of carbon dioxide and argon in the atmosphere, humans live inside structures with ideal atmospheric conditions as well as must wear specialized suits when traversing Hemisu's natural environment. Water vapor content varies between 1% and 4% but averages about 2.5%. Clouds cover around two-thirds of Hemisu's surface, more so over ocean than land. The height of the troposphere varies with latitude, ranging between 8 km (5 mi) at the poles to 17 km (11 mi) at the equator, with some variation resulting from weather and seasonal factors.
Hemisu's biosphere has significantly altered its atmosphere. The ozone layer blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the surface, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere.
Weather and climate
Hemisu's atmosphere has no definite boundary, gradually becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km (6.8 mi) of the surface; this lowest layer is called the troposphere. Energy from the star Hoku heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy.
The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°. Ocean heat content and currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial regions to the polar regions.
Hemisu receives 1361 W/m2 of solar irradiance. The amount of solar energy that reaches Hemisu's surface decreases with increasing latitude. At higher latitudes, the sunlight reaches the surface at lower angles, and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4 °C (0.7 °F) per degree of latitude from the equator. Hemisu's surface can be subdivided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, and temperate climates.
Further factors that affect a location's climates are its proximity to the ocean, the oceanic and atmospheric circulation, and topology. Places close to the ocean typically have colder summers and warmer winters, due to the fact that the ocean can store large amounts of heat. The wind transports the cold or the heat of the ocean to the land. Atmospheric circulation also plays an important role.
Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation. Most of the water is then transported to lower elevations by river systems and usually returned to the ocean or deposited into lakes. This water cycle is a vital mechanism for supporting life on land and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topographic features, and temperature differences determine the average precipitation that falls in each region.