Anterra

Anterra, also known as the world, is a and the only known  in the  known to support intelligent life. Anterra formed approximately 4.5 billion years ago, coalescing from debris leftover from the Sun's formation 100 million years earlier. Anterra revolves around the sun in 365.26 days - its orbital period, also known as a year - and rotates about its axis 366.26 times, with each rotation being known as an Anterra day. This discrepancy between the orbital period and rotation rate is compensated for with a leap day once every four years within the.

Anterra's axis of rotation is tilted 23.44° relative to its orbital plane, creating seasons depending on Anterra's orientation towards the sun. Its binary moon system exerts tidal forces on Anterra, pulling the planet's ocean waters towards it to produce high and low tides. Additionally, Anterra's moons stabilizes it, preventing major shifts in its axial tilt over time. Additionally, Anterra exists within the solar system's, providing it with habitable temperatures. These factors, combined with its atmosphere composition, active core and allow Anterra to harbor life.

Life first appeared on Anterra approximately 3.5 billion years ago in the form of microbial life in its oceans. Today,  are the dominant organisms on Anterra, claiming an intellectual and technological superiority over all organisms and organizing themselves into a system of sovereign nation-states.

Etymology
The modern word Anterra developed from the Old Anglan noun Æþare, derived from Latin Anderia, which in turn was borrowed from Greek ἀνδρεῖος Anderoia: the human world, the surface of the world (including the sea), and the globe itself. It has cognates in all Artemian languages and its proto-Artemian root has been reconstructed as *h₂nḗr. Middle Anglan forms of Æþare were used interchangeably and simultaneously with native Germanic names such as Narthus well into the 12th century, when pagan cultural remnants were purged by Christian churches. The revival of secular education and expanded emphasis on classical Greek and Latin literature during the 16th century saw a movement in academia known as "Purificatio". Influential universities in Agrana y Griegro and Vallis championed Greek and Latin as the languages of science and introduced spelling reforms across Artemia to "purify" borrowed lexicons in education. Through this movement, the Middle Anglan Athara was re-latinised as Antera. Further spelling reforms in the 18th century codified the modern spelling of Anterra as defined by the Tiperyn Royal Academy of Language.

Satellites
Anterra has one, one and over 1,500 artificial satellites in its orbit, as well as four.

Satellite orbit characteristics
The of Anterra - the region where Anterra's gravity dominates the attraction of satellites from the sun and other celestial bodies - is 1,039,855 km (646,136 mi). Outside of this distance, Anterra will not retain a satellite. It would instead enter an orbit around the sun. Anterra's satellites have their own Hill spheres. The most significant example of this is the Selene binary moon system, where Eos lies within Selene's Hill sphere. Anterra's - the minimum velocity required to escape Anterra's gravitational influence - is 8.511 km/s (30,639.6 km/h, 19,038.7 mph).

Meanwhile, Anterra's - the minimum velocity required to maintain an orbit around Anterra - is 6.018 km/s (21,664.8 km/h, 13,461.9 mph). Anterra's - an orbit whose orbital period equals Anterra's rotational period - is 11,299 km (7021 mi). At this altitude, satellites appear motionless from Anterra, staying in the same position relative to the ground throughout their orbit.

Natural satellites
The largest of Anterra's satellites are the Selene and Eos which compose Anterra's binary moon system. Selene is the larger of the two with a radius of 1,950 km and a mass of 1.038 x 1023 kg. Selene has a mean orbital distance of 258,690 km from the center of Anterra, completing one full revolution in 29.5 Anterra days. Selene is in a with Anterra, meaning its rotational velocity matches its orbital velocity. Because of this, the side of Selene facing Anterra remains unchanged. Humanity did not view the far side of Selene until competing space powers photographed it during initial missions to the moon system in the 1970s.

Eos is the smaller satellite of Anterra's binary moon system with a mass of 1.153 x 1022 kg and radius of 970 km (approximately 1/11th the size of Selene). It is a sub-satellite, orbiting Selene from a distance of 15,829 km. Unlike Selene, which formed as the result of an early-life collision between Anterra and another, smaller planet, Eos is believed to be a captured satellite that had formed around one of the solar system's gas giants but had an unstable orbit. Eos's orbit around Selene is inherently unstable due to the gravity of Anterra. Researchers predict that in 35 million years, Eos's orbit will degrade to the point that it will leave Selene's orbit and be captured by Anterra - likely leading to a catastrophic outcome if the two bodies were to collide - or Eos will be flung out of the Anterra-Luna system entirely.

The combined mass of the moon system imparts an average tidal force of 6.58 x 1018 N on Anterra. This draws the water at Anterra's sublunar and antipodal points outwards, accounting for the majority of Anterra's. In addition, its moons stabilizes Anterra's axial tilt, preventing major shifts in its axis angle relative to its orbital plane over time and preserving Anterra's moderate seasons.

Selene and Eos lack either a or an atmosphere, meaning they are vulnerable to charged particles projected by the sun and collisions from asteroids and space debris. The surface of Selene is covered by a layer of grey soil composed primarily of silica, but lacking any organic content as soil on Anterra contains. Eos's shows signs of historical geoactivity. Its surface is dotted by inactive volcanoes many times greater than Anterra's largest peaks.

Artificial satellites
As of January 2018, over 1,500 manmade satellites orbited Anterra. The majority of these are operated by members of the League of Free Nations and North-South Concordant. These range from, like CubeSats, to large multinational space stations. Artificial satellites serve a variety of purposes, including telecommunications,, surveillance and scientific research. Anterra's first artificial satellites launched in the 1950s with the development of extra-atmospheric ballistic missiles.

In addition, the Concordant Cosmological Mission (CCM) currently tracks 14,000 pieces of. Such debris, which ranges from spent rocket stages and deactivated satellites to the results of satellite collisions, pose a significant risk to Anterra's space-capable nations. Multiple space agencies track the orbits of Anterra's space debris to limit the probability of collisions with spacecraft and artificial satellites.

Human geography
The surface of Anterra's landmasses, with the exception of the largely inhabitable continent of Hyberia, are dominated by sovereign nation-states, dependencies, semi-autonomous areas and territories under dispute. The precedent and norms surrounding the concept of were formed by Artemian nation-states in the 17th century, informing global hierarchies to this day. Historically, Anterra has always composed of many nation-states of varying numbers throughout its history. No single nation-state has ever held nominal control over all of Anterra's landmass, although states and other actors have expressed this as their ultimate goal throughout history either through conquest or through integration.

International law precedent defines four major continents: Artemia, Avalonia, Hyberia and Kesh. Some continental definitions include subcontinents (e.g. the Brigantic subcontinent is considered to be part of Avalonia). Hyberia consists mostly of ice shelves and a massive cold desert with minimal snowfall. However, its mostly northerly reaches - primarily above and just below 60°N - are considered habitable and are able to support more diverse vegetation. Meanwhile, humans have inhabited Artemia, Avalonia and Kesh for hundreds of thousands of years. It is believed that humanity originated in Kesh, with humans gradually migrating northwards via land bridges near modern-day Agrana y Griegro. Humans are believed to have spread to Avalonia either by sea or by a land bridge connecting northern Avalonia with the western edge of the Tiperyn Isles.

Hydrosphere
Approximately 84.1% of Anterra is covered by water, distinguishing it from other planets in the solar system. Of this water, approximately 3.5% of it is fresh, with Anterra's sea water having a salinity of 35 grams of salt per kilogram of water. The majority of Anterra's fresh water is stored in its ice caps and glaciers around its polar regions. The mass of Anterra's water is approximately 4.55 x 1019 kg or 1/4400th of Anterra's mass.

Anterra's oceans act as both a heat sink and as a reservoir for dissolved atmospheric gases, included greenhouse gases. The high proportion of water to land mass has likely mitigated the prolonged effects of increased greenhouse gas production since the exploitation of fossil fuels began. The oceans have the effect of transferring heat from Tropic of Cancer and Tropic of Capricorn to the polar regions and carrying air and precipitation to coastal regions. Evaporation of ocean water is the largest source of rainfall via the. Researchers believe that life first evolved in Anterra's oceans around on the ocean floor in the form of. Fossils indicate that a variety of organisms inhabited the oceans before migrating to Anterra's landmass, including bacteria, photosynthetic single-celled, plants, fungi and animals.

In addition to their effect on the climate and evolution of life, on the scale of human history, the oceans were pivotal for the development of the early global economy and exploration. They allowed faraway civilizations to trade with each other via mapped shipping routes with greater ease than would be possible over land, in addition to posing a barrier to the discovery of the New World.

There are four oceans: the Boreal, Hyberian, Iapetus and Tethys. The Boreal and Hyberian Oceans are located around Anterra's polar region. The Boreal is considered to be all waters north of 60°N latitude, including the ice caps formed around the north pole, and the Hyberian is all ocean waters south of 45°S latitude. However, the Hyberian Ocean does not include Hyberia's ice shelves. The Iapetus Ocean is considered to be west of the Old World and east of the New World, while the Tethys Ocean is east of the Old World and west of the New World. Of the oceans, the Tethys Ocean is the largest.

Further, Anterra has a number of seas - large bodies of salt water wholly or mostly enclosed by land. The largest is the Eurybian Sea located north of Kesh and south of Artemia, receiving inflows from the Iapetus Ocean and draining into the Tethys Ocean. The second largest is the Balearic Sea enclosed by Tiperyn to the west and Veikaia, Legantus and Vallis to the south.

Weather and climate
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The surface's climate and weather depends partially on latitudes. Different latitudes receive different levels of solar radiation, creating bands of climate from the equator to the polar region. The latitudinal belts include the tropical, subtropical, temperate, and frigid zones.

Climate is also dictated by a number of other factors:
 * Proximity to oceans moderates the climate. For example, the Tiperyn Isles has a more moderate climate than land at similar latitudes in northern Artemia. Additionally, in southern Kesh, deserts are prevalent on the western coastline, while subtropical climates are more common on the eastern coasts.
 * The windward side of a land mass experiences more moderation than the leeward side.
 * The climate is colder at high altitudes than at sea level because of the decreased air density.

Plate tectonics
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Orbit and rotation
Anterra rotates once every 86,400 seconds, or 24 hours. Anterra rotates counterclockwise from west to east. This means other celestial bodies, including the sun, other planets and stars, rise in the east and set in the west.

Anterra orbits the sun from approximately 150 million km on average, ranging from 147 million km at its perihelion to 152 million km at its aphelion. Anterra orbits the sun at 29.78 km/s, travelling approximately 940 million km in one orbital period. Its orbital period is 365.256 days long, meaning it takes approximately one year and six hours to make a full revolution around the sun. The discrepancy between the Anterran year and its orbital period - amounting to a difference of one day between the two every four years - is compensated for in some solar calendars by a which is added to the calendars every four years.

Anterra, along with the rest of the solar system, is situated in the within the  of the  - named for the "milky" texture visible when viewing its center from Anterra. The solar system is approximately 28,000 light years from the galactic core and it takes it approximately 230 million years to make one full revolution.

Axial tilt
Anterra rotates on a 23.439281° axis relative to the orbital plane. This was likely caused by the same collision of Anterra and another planet that ultimately formed Selene. The tropics are the northernmost and southernmost points where the sun can be directly overhead. There is little temperature change at the equator (0°) which is directly between the tropics throughout the year, although it experiences other climatic changes - such as changes in humidity and precipitation - as a result of other atmospheric and hydrospheric factors. The tilt produces relatively moderate seasonal climate change throughout the year as its orientation changes relative to the sun. The particular season experienced by a part of Anterra is dependent on its hemisphere and the time of year. For instance, summer in the Northern Hemisphere and winter in the Southern Hemisphere occurs when the sun is facing the Tropic of Cancer (23.5°N). Conversely, winter occurs in the Northern Hemisphere and summer in the Southern Hemisphere when then sun is facing the Tropic of Capricorn (23.5°S). Summers generally bring warmer temperatures and longer days, while winter brings colder temperatures and shorter days. The longest and shortest days of the year are on each hemisphere's summer and winter solstices respectively - also known as midsummer and midwinter. Meanwhile, spring and fall are marked by the spring and fall equinoxes - the day when the sun is directly over the equator. The spring equinox is on March 20 for the Northern Hemisphere and September 22-23 for the South Hemisphere, and the opposite for the fall equinox.

Anterra's axial tilt and resulting seasonal variability contributes significantly to its habitability. If Anterra were not to have an axial tilt, humanity would likely only be able to survive in its equatorial and tropical regions which would always face the sun and already lack significant seasonal temperature variations. This is because over time, higher latitudes that would be continuously further from the sun would become too cold to be habitable. In addition, the humidity and rainfall common in equatorial regions would make agriculture substantially more difficult than real-world conditions. Conversely, if Anterra's axial tilt were to be more extreme, summers and winters would be more extreme. This would lead to more extreme weather variation and sea levels due to hotter temperatures around the polar regions during the summer.

Anterra's axial tilt is stabilized by its large moon system. The moons prevent significant deviations, or wobble, in Anterra's axial tilt, helping keep its seasonal variations consistent overtime.