Thalia is a temperate terra located in the core of the Via Sagittaria Galaxy. The planet acts as the capital of Sagittarium while also being the closest continually-inhabited natural body to Nocturne. It is the home world of an artificial race called the Thalians. With a population of 1.2 trillion individuals on its surface and a total of 1.2 quadrillion orbiting it, Thalia is the most heavily populated planet in the core.
The planet is a center of trade in the region. The planet and its system has a large amount of infrastructure such as wormholes leading to the central black hole, a SICTIRIAD Generator nearby to it, as well as huge space ports handling the importing and exporting of huge amounts of resources.
The planet was first colonized by the Yohjan Confederacy in 908 BCE, to secure their claims to the Nocturne black hole. A fairly small number of troops were stationed on the planet where they all lived under the same small dome. During the War of the Final Transition, it was reinforced several times with the population growing to almost one million by 0 CE. This same year, the YoC collapsed and Thalia was cut off from the rest of the Via Sagittaria. There was over a century of light lag and three centuries of travel with their relatively small ships.
The planet's population had to develop on their own. After over one thousand years, they began producing their own ships again and had even terraformed the world. It soon became the capital world of the Vaplein Republic, a nation made up of the descendants of the original soldiers living on Thalia.
In 20,677, Klein Vay, with the support of both the State of Tenshi and Drusidia, staged a coup on the planet and established the nation of Sagittarium. The planet became the de facto capital of Sagittarium for several hundred years. In this time it was fully terraformed and became the most important planet in the nation. Its population quickly reached one trillion with most of the population after that living in orbit due to exorbitant land-prices on the surface of the planet.
The planet is currently a center of trade and acts as a gateway to the Nocturne. Large numbers of spaceports cover the planet serving as areas to transfer resources as well as import resources to Thalia itself. In addition to these space ports, there are quadrillions of independent objects orbiting the planet, so many objects that Thalia appears hazy from most viewpoints.
2.4 billion years ago, Thalia formed out of the protoplanetary disk of its parent's star, a yellow dwarf named Vay's Star. The planet would have likely supported life were it not located in the core, however, it never had a chance to form even bacteria in its long history. Two million years ago, a fairly large moon strayed too close and Thalia tore it apart to form rings.
The planet was first claimed by a nation in 908 BCE, when the Yohjan Confederacy landed a small detachment of troops onto the world with the goal of gaining influence over the core. It was the closest planet to the core with a stable orbit, so it was the logical choice for colonization. The planet remained unterraformed during this initial period of colonization, it was little more than a military base.
The planet had a wormhole built near it to further secure the Confederacy's claim over the area. This wormhole lead to Aegyn, the capital of the Yohjan Confederacy. Shortly thereafter, in 405 BCE, however, the wormhole was deactivated and it was destroyed on Helyar's side. The soldiers were left stranded and remained working as they have been. They expanded the base, which was mostly just a series of small domes, and built some more small infrastructure.
The population remained the same during this period of isolation. The commander managing the base strictly ordered the soldiers to remain in a state of readiness as well as wait vigilantly for the return of communication. When it became apparent that the Yohjan Confederacy was not coming back, they became a sort Junta state in which the military, which were the only people on the planet, began ruling. They started adapting military technology to gather resources such as oxygen from rocks and aluminum for more parts.
As Sagittarium expanded, the number of habitats increased by dozens of times. From far away, the planet's characteristic haze began to form, a haze composed of trillions of orbiting objects. Normally, governments reduce the clutter of the area around planets by incentivizing migration to other worlds. Sagittarium, however, most likely made heavy use of cloning to create colonists. Thalia likely once housed many now-illegal cloning facilities meant to bolster the population. It would have been cheaper to use mostly automated craft and arms, but, being ever the cautious nation, Sagittarium opted to only have partially automated fleets. All important crafts were required to be piloted by individuals and all factories required supervision, hence the need for more individuals.
Thalia is home to a "race" of androids known simply as Thalians. They were designed to subtly influence the population into being much more nationalistic and loyal to the Chancellor. Thalians were fully sapient, however, their opinions regarding the state and politics was always the same. They were tools of the state and were incapable of resisting its will. This extreme loyalty caused many around them to also become more loyal, simply because of the human desire to fit in. Thalia had the highest population of any planet throughout Sagittarium's history, while also having the highest concentration of Thalians at over one percent. Despite this, the existence of Thalians was kept a secret for the majority of Sagittarium's history (even after democratization).
The planet continued increasing in population and has never once experienced a year of population decline. Even with the declining power of its host nation, the planet kept increasing in population. As one of the most stable and safe places to live in the galaxy until well after 35,000, Sagittarium saw large numbers of civilians from other nations migrate to it. This constant influx of ideas and hard-to-control foreigners was a security risk, but the benefit of having a larger population far outweighed the risks.
When Sagittarium became a part of the Confederacy of Borealis, the population began to rival that of the typical home world of most species. Since this point, it has ranked in the top ten for population in the Via Sagittaria (when including those that orbit the planet). The Founder's Council destroyed itself shortly thereafter, detonating 10 hydrogen bombs on Thalia to destroy their facilities. At the same time, many satellites deorbited. This event was mostly harmless, resulting in few casualties. The Chancellor's palace was fitted to become the new Capitol building and much of the government-owned land was sold to raise funds for refitting various government buildings.
The planet has remained fairly stagnant since its days as the capital of an authoritarian regime. The number of individuals and the infrastructure around it has continued to grow for millennia, with only a handful of years seeing negative growth.
Thalia has 4 major continents, all named after members of the quasi-legendary Founders of Sagittarium. These continents are Stirner, Cheng, McCrea, and Perez, listed in order of size. There are thousands of islands scattered across the planet as well. Most of the land on the continents is used for governmental purposes or have been converted to nature-preserves. These islands, however, were sold to wealthy individuals as status symbols. Bested only by a handful of worlds, land on Thalia is remarkably expensive. The largest islands can be worth more than the cost of terraforming worlds.
There are only a handful of cities on the planet, the largest one named after a mythical figure, Satoru, was established before the creation of Sagittarium. It started as a lonely dome on the planet, but its strategic caused it to end up becoming on the of the most important bases on the planet. It is where the majority of the government lies as well as where the Congress meets. Other large cities include Gurren, Jei City, Dolorous, and Habir.
The huge number of craft around Thalia present fairly unique logistical issues. Collisions are very dangerous and Kessler Syndrome is an ever-present threat. Over the north pole of Thalia, there is a "no-orbit zone" meaning that no craft can have a low-Thalia orbit in that area unless authorized by the state. This is to allow at least a fraction of the planet to always remain clear in the event of a disaster. Large computers coordinate the ships to prevent collision, and ships and other orbiters are required to have automatic collision avoidance systems. Large craft, called "Janitors" possess hundreds of powerful lasers capable of vaporizing debris. There is constantly large amounts of debris orbiting Thalia, hence the need for these Janitors. They are only permitted to target objects which are not emitting the proper signals to prevent the accidental destruction of a ship carrying people.
Spaceports are hubs of activity and commerce. The largest of which accumulate trillions of individuals living on their surface. This stems from the tendency of individuals having their habitats or orbiters conglomerate around larger objects. They often directly link to the largest object similar to how protoplanets form in a star system. Small ships often link together and these new "clumps" often dock on even larger ships. The largest collections of linked craft are several hundred kilometers in length, width, and depth while housing upwards of ten trillion inhabitants. These orbiting cities are covered with modules operating under their own spin and, therefore, gravity.
Orbital rings often have their cores spin at higher rates as ships dock onto them (as larger mass means a higher spin is needed). Orbital rings, just like spaceports, and commonly docked on. The most docked-upon sections of the orbital rings can be seen from the surface even during the day.
Thalia orbits a fairly small yellow star. It orbits at a rather manageable distance, and it is the farthest planet from its star. The reason for this is simple, the higher quantity of stars means that close encounters are very common. This causes Oort clouds to be fairly rare and constantly disturbed, but also causes all but the most tight-knit systems to lose their planets. There was one planet, Jezreel, that once accompanied Thalia at an even closer orbit as a hot mini-neptune. Jezreel has since been moved to another area in the core and the rest of the system had been cleared.
The largest building on the surface of the planet is the Chancellor's Palace. It has 55 cubic kilometers of space. The largest room is the Congress Hall, a room so large that large vents and fans control what would otherwise be a micro-climate. In the ceiling of this room is a large glass window with the purpose of letting in natural light. Other rooms are dedicated to housing aids to the congresspeople, storing historical documents, and a subsection dedicated to the living of the modern Chancellor.