Mercury
Once thought to be tidally locked to the Sun, with a light and dark side, it is now understood that Mercury's entire surface is exposed to the sun's heat at certain points. The polar regions, oddly enough, remain cool enough to make settlements possible. Mercury was colonized in the early 2300's by groups fleeing the wars of consolidation on Mars. Two settlements exist on Mercury; "Dar-ul-Muraqab" on the northern pole, and "Chandra" on the southern pole. These two very different colonies have maintained peace by keeping to themselves, though Chandra is definitely the more outward looking of the two.
Chandra was established in 2305 by the "Chandra Enterprise", a major Martian business entity which stood to lose much of its power and influence under UMA rule. To avoid this Chandra simply relocated all of its industrial operations, facilities, staff, and families to the south pole of Mercury. It has taken advantage of almost limitless free solar energy and the ample resources of Mercury's crust to become the single largest industrial concern in the solar system. Chandra has a population of about four million people, half of whom are employees of Chandra or its many subsidiaries. Chandra is run as a corporate concern, regarding itself as the bastion of free enterprise and the inheritor of the American can-do spirit. This attracts a wide range of people from throughout the solar system, though they often find life here to be more difficult than they imagined. Dar-ul-Muraqab was founded in 2320 by a group of Martian dissidents, Sufi Muslims who refused to accept rule by what they saw as UMA's Mareekhi apostasy. Rather than submit and blend in, or be exterminated in pointless warfare, they opted to resettle offworld with Belter assistance. Unwilling to join with the secular humanists of the Free Luna Soviet, they eventually chose Mercury. On Mercury, they immediately created a Sufi community run according to Sharia law. While Dar-ul-Muraqab is self-sufficient in energy and metals, it relies on foreign trade to supply food and most organic materials. To this end, many residents work in conjunction with Chandra on solar power grids, mining, and operational support. There are currently about one million colonists at Dar-ul-Muraqab, which has become a center for religious scholarship. In addition to Sufi Islam, members of traditional Christian and Jewish groups find Dar-ul-Muraqab to be a suitable place to practice their own faiths, due to its very traditionalist approach to life and religion.
Venus
Venus was already immensely hot before the Sun became unstable in the 21st Century, and the Sun's increased output has only made it more so. Venus was briefly the subject of a terraforming attempt in the 2050’s, but this was quickly abandoned as pointless and impractical. Little work is performed on the surface of Venus, as it is a hellish environment that even the technology of 2500 cannot survive for long. In modern times, there are numerous ruggedly built balloon habitats (called "aerostats") for research and extraction of useful atmospheric gases. These free-floating habitats can house a few hundred people each. They drift about fifty kilometers above the surface, up where the pressure and temperature are both moderate. These aerostats perform a valuable service, extracting carbon, nitrogen, and other elements from the atmosphere for use on other colonies where such materials are occasionally scarce. The Free Luna Soviet, UMA, Chandra and even the Belt League all maintain at least one aerostat habitat on Venus. Several aerostats are actually independent settlements, loosely affiliated with Belter clans.