Solar Planetary System
Centaurus Sector, United Federation of Planets

Primary: Sol
Star type: G2V (Main sequence yellow dwarf)
Star generation: 3
Planets in system: 10
Total sapient population: ~ 10 billion

The system of planets surrounding the star Sol is a fairly typical planetary system for a G-class main sequence star, consisting of an inner set of relatively small, rocky planets and an outer system of gas giants. Two of the system's planets support indigenous sapient life. Of those, by far the best-known in the galactic community is Sol III (Earth), which is one of the 17 worlds known to be subject to parallel human evolution.

Since Earth-humanity's contact with Salusian explorers in SY 1999, human, Salusian, and other engineers have worked to terraform a number of the Solar system's other bodies to support permanent colonies.

A brief overview of the system's planets and other inhabited bodies follows.

Sol I (Mercury)
Class: D
Population: See below
Independent: No
Governing polity: Earth Alliance

Mercury supports only a single permanent settlement: Station Helios, a scientific station operated by the Earth Alliance government for the purpose of monitoring Sol. The station's normal operating complement is 10 personnel, who are rotated in and out in two-year stints. The planet has no full-time inhabitants and no legal structure for same.

Sol II (Venus)
Class: M (Terraformed; originally Class N)
Population: 150 million
Independent: No
Governing polity: Earth Alliance

Venus was the second planet to be terraformed during the First Expansion. Terraforming operations began in SY 2005 and were declared complete in SY 2017. The effort can be deemed only a partial success. While the planet did become Class M, capable of supporting human life without technological intervention, it remains a place of near-constant overcast with very rainy conditions and a high mean humidity. The majority of humans find it both uncomfortable and gloomy. Venus became independent in 2165, but its citizens voted to join the Earth Alliance willingly when that body was formed in 2390.

Sol III (Earth)
Class: M
Population: 6 billion
Independent: Yes
Governing polity: Earth Alliance

Evolutionary homeworld of the Solar human species, Earth has gone from an obscure planet of interest only to a few Centauri, Vulcan, and Salusian explorers to one of the driving forces of galactic culture and politics in only a bit more than 400 years. Like most natural Minshara-class planets, it is a place of widely varying climate and condition, and has produced an adaptable and hardy race of people. Its population has varied wildly over its time as a galactic player, ranging from a high of more than 15 billion in the early 21st century to a low of about 3 billion at the end of the War of Corporate Occupation. Immigration from former colonies, advances in medical technology, and a high birthrate saw that population double in the first few stable years after the war.

Sol IIIa (The Moon)
Class: D
Population: 250,000
Independent: No
Governing polity: Earth Alliance

Earth's only natural satellite had the honor of being Earth's first permanent colony. Though humans first visited the Moon in SY 1969, it was not until the year after First Contact, SY 2000, that a permanent settlement, Tsiolkovskiy City, was established. Interestingly, the Moon's four major cities (all of the domed-crater variety) are all located on the side of the Moon that cannot be seen from the surface of Earth, so that the satellite continues to show its familiar face to the citizens of the mother planet. The lunar colonies have never sought independence.

Sol IV (Mars / Malacandra)
Class: L (partially terraformed: once Class M, Class K pre-Earth colonization)
Population: 10 million
Independent: Yes
Governing polity: Malacandra Free Republic

When Earthmen arrived on Mars in SY 2002, intending to make the planet their homeworld's first non-satellite colony, they were unaware that Mars already had a native sapient species. In fact, it had three of them, plus a group of previously arrived extrasolar invaders, all of whom pre-dated the rise of Earth's humanity to sapience and all of whom had been driven into underground hibernation by the planet's shift to Class K. A very confusing war resulted when the humans diligently began terraforming the planet, only to awaken the hibernating native Martians in the process. Eventually a peaceful accommodating was reached in which limited terraforming was permitted to go forward and the human colonists were permitted to stay while the surviving Martians resumed their place in galactic society. Today, most native-born Martians of indigenous and colonist stock alike prefer to be known as Malacandrans after the indigenous word for the planet. In 2390, the Malacandran government declined to join the Earth Alliance. When the EA cracked down on internal dissent in 2406, Earthforce declined to press the issue.

Sol V (Jupiter)
Class: J
Population: 3 billion (see below)
Independent: No
Governing polity: Earth Alliance

Jupiter itself is not inhabited except for a handful of tibanna gas mining platforms in the upper atmosphere, each of which, though a permanent installation, has no full-time population. However, four of its satellites do support rooted colonies:

- Europa, Class M (terraformed from Class L), population 1 billion
- Ganymede, Class M (terraformed from Class K), population 750 million
- Io, Class N, population 350 million (domed-crater settlements)
- Callisto, Class L (terraformed from Class K), population 900 million

Sol VI (Saturn)
Class: J
Population: 275,000 (see below)
Independent: No
Governing polity: Republic of Zeta Cygni

Like Jupiter, Saturn has no permanent population itself, but supports a handful of gas mining stations and has rooted colonies on several of its satellites:

- Titan, Class M (terraformed from Class N), population 250,000
- Rhea, Class D, population 20,000 (domed city)
- Enceladus, Class D, population 5,000 (domed city)

The government of the Sol VI Territory of the Republic of Zeta Cygni has considered petitioning the Territorial Office for backing to terraform Rhea, Enceladus, and Dione, but the current political situation vis-a-vis the Earth Alliance makes the prospect of attracting populations to make the projects worthwhile questionable at best, so for the time being the project has been tabled. The rumors that Mimas is actually an armored space station intended as a final line of defense were effectively dispelled when it was not employed in the Battle of Titan (2406), but instead just sat there like the pockmarked rock it is.

Sol VII (Uranus)
Class: J
Population: None

There was one colony in the Uranian system, established on the moon Oberon in 2072. The colony was not an economic success and was abandoned in 2123. Since then, no further attempts have been made to colonize the moons of Uranus. There are unconfirmed rumors that the Earth Alliance has considered establishing a colony on Titania in an attempt to waylay careless travelers bound for Titan. These are probably false.

Sol VIII (Neptune)
Class: O (terraformed; originally Class J)
Population: 150,000
Independent: No
Governing polity: Earth Alliance

Neptune was the subject of one of the stranger third-generation terraforming experiments: In 2303, the GENOM Corporation's Earth branch launched an ambitious effort to convert the former gas giant into an aquatic world. The experiment was successful, but strangely, people are not exactly lining up to go live on a waterworld such a staggering distance from the system's primary star. The colony passed out of corporate ownership after the War of Corporate Occupation, and the Earth Alliance has never shown any particular inkling that it knows what to do with it. The Neptunians who did show up, though, are a hardy and individualistic bunch, and have so far resisted subtle and not-so-subtle efforts by the EA government to get them to move someplace more convenient.

Sol IX (Pluto/Charon)
Class: D
Population: See below
Independent: No
Governing polity: Earth Alliance

The twin planetoids of Pluto and Charon were almost kicked out of the official list of planets once, not long after First Contact, but eventually a compromise was reached whereby the two were collectively recognized as a "double planet". Cold and hostile even for a Class D planet, Pluto/Charon is home to one of the Earth Alliance's largest starship construction yards and an extensive Earthforce Navy base, but has no permanently settled population - only military personnel who are assigned there. Charon is also the location of one of the EA's key Solar System Monitor/Distant Early Warning sensor stations. All told, approximately 20 million Earthforce personnel are stationed at Pluto/Charon at any given time.

Sol X (Persephone)
Class: T
Population: 100 million (see below)
Independent: No
Governing polity: Earth Alliance

The super gas giant Persephone is not itself inhabited; however, its only satellite, Yuggoth, was once the home of a long-extinct civilization pre-dating even Martian sapience by at least 300 million years. It is believed that this civilization was not, in fact, Solar, but that Yuggoth was once a planet in a star system which has since been destroyed, and that it spent some time as a rogue planet before drifting into the Solar system and being captured by Persephone's gravity. The moon was first explored by humans in 2033 and the first permanent settlement was established in 2102. So far from Sol that it is not even the brightest star in the local sky, Yuggoth is a Class K planetoid and its citizens live in a single underground city, Yith.

Other settlements

The remainder of the Solar system's population is scattered throughout the system in various unconnected settlements, including small domed cities on some of the larger asteroids in the Sol IV-Sol V belt and space habitats at a number of the system's key Lagrangian points.

Other interesting facts about the Solar system

The Solar system once had an eleventh planet, Mondas, which was Class M and orbited at a distance of 1 AU directly opposite Earth. This world was also home to Solar humans - apparently another parallel evolution strand - until it was cast adrift by an unknown cosmic accident, possibly coinciding with the arrival in the Solar system of Yuggoth. Mondas is known today as the homeworld of the Cyberrace and has been artificially installed in a stable orbit around Wolf 359.

Another little-known fact about the Solar system is that it actually contains two stars. The other, Nemesis, is a red dwarf star (spectral type M) of sufficiently lesser mass that it orbits Sol in the fashion of a planet rather than forming a traditional binary star arrangement with it. Its orbit lies beyond the Solar system's Oort cloud, at a distance of approximately 100,000 AU. Nemesis has no planets of its own. Its orbital period has been implicated in the cause of several mass extinction events on Earth, but the data supporting this conclusion are still scanty and the matter much disputed.

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