Mars

Mars is the fourth planet in the Sol system and humanity's oldest interplanetary colony. Although the planet has a tumultuous history, it has developed into an industrial powerhouse and one of the most important worlds to the United Nations Space Command as it houses the headquarters of key military-industrial contractors such as Misriah Armory and Reyes-McLees Corporation alongside commercial megacorporations like Traxus Heavy Industries. As one of the earliest and most developed human colonies, Mars is also one of the few worlds outside Earth to have significant clout in the United Earth Government.

Early days
For millennia, Mars held a lofty position within the cultures of humanity, though it was not until the 20th century that clear images of the planet were broadcast to the citizens of Earth. Throughout the later decades of the century, human space exploration blossomed into a myriad of unmanned satellites orbiting the planet conducting surveys and scans of all kinds - preparing for the inevitability of a human colony on the red planet. This answer came in the late 2010s and early 2020s, with the launching of three manned missions in 2018, 2021 and 2023 aimed at conducting scientific expeditions. Each mission consisted of roughly 15-35 personnel, slowly expanding in scope per successive mission as each rocket brought with it more infrastructure and supplies to slowly build up the colony base located inside the lava tubes of Arsia Mons. These missions were short duration in nature, lasting only a few weeks each before returning their crews to Earth.

As the 2020s continued in earnest, more contracts for space exploration were granted to the various corporations of Earth - establishing vital space infrastructure in orbit in preparation for continued scientific and industrial interest in space travel. More pioneer groups began to land across Mars as the decade continued, until the discovery of a lifetime was announced. On May 3, 2027, Firegrove Industries' CEO Christopher Leto announced the discovery of what was believed to be a microorganism native to the Martian underground permafrost; life outside of Earth. The discovery lit a fire on Earth, and effectively overnight, trillions began being poured into fledgling space programs and industries the world over. The boom of Mars landings was effectively uncontrolled, and as such any hope by the scientific community of a slow and ordered approach to exploring the planet were ignored. Settlements were scattershot across the planetary surface in a cluttered effort to cover as much area as possible and recover more samples for study. Such samples proved extremely difficult to find, and after the first five years of searching almost no further traces of Martian life were found. Claims arose that Leto's announcement was a fake, or that his team had misidentified Earth life brought to the planet as an example of interplanetary contamination. In 2042, these claims were proven correct as anonymous sources within Firegrove leaked a series of documents proving with no doubt; the Martian bacterial samples claimed by the company were not only mis-attributed Earth life, but that the samples had been genetically engineered and tampered to appear more convincing to the scientific community. The hoax had increased Firegrove's profits tremendously, and seen a huge investment in Earth's space programs - at the expense of Martian contamination and scientific integrity. The scandal blew up and Firegrove was practically dismantled overnight.

The legacy of what would later become referred to as the "Martian Gold Rush" was a mixed one, with long-spanning effects on Mars' development. The disorderly nature of settlement on the planet (and the subsequent abandonment of these sites) meant that much of the planet's surface was littered with human artificial waste. A number of small nonviolent clashes over land rights on the planet had also given rise to an effective sense of "frontier justice" - many Martian explorers routinely carried firearms for their own self-defense - though none had yet to be discharged in anger. Perhaps most of all, the microbe which had been "discovered" on Mars by Firegrove back in 2027 had proven well-adapted to the Martian environment, and was beginning to slowly but surely spread across the surface - effectively destroying all chances for a search for native Martian life. With a multitude of corporations and nations pulling out of Mars in the wake of the Firegrove scandal in favour of alternatives such as Luna, interests in Mars fell and investment in the planet took a nosedive.

The mid-2040s were bereft with the Kasimov Crisis - an event in which settlers on the Martian surface refused to pull out and return to their homes on Earth, attempting to declare themselves independent of their home nations and encourage a Martian independence movement. The seven colonists were ultimately subject to a four-week siege conducted by corporate security forces, before their shelter supplies ran out and they surrendered themselves to return home and face arrest. The following year, a dedicated colony site was founded at Arsia Mons at the site of the initial Mars landings 25 years prior, marking the start of what is now considered to be a "true" Mars colony. Unlike previous efforts, the Arsia colony was to be a dedicated effort organised by the Chinese government hoping to lead the way in Mars exploration. In the following decades, American and European efforts would crop up in the Mariner Valley, Tharsis region and Hellas Basin, with a myriad of small mining and industrial operations beginning to develop to support the burgeoning population. The relative lack of investment and the ordered nature of the colony efforts - hoping to avoid the chaos of the 2030s - saw a time of relative quiet, as scientists and explorers were to keep primarily to the regions surrounding their home bases.

Phobos
For centuries, Phobos has served as the "gateway" to Mars and the planet's primary orbital port. The moon is hollowed out and almost entirely built up.

Deimos
After plans to convert the moon into a massive intrasolar cargo transport or a slower-than-light colony ship fell through, Deimos was turned into the orbital counterweight for the Tharsis industrial heavy-lift array.