The Sol System, even in the wake of the Terran Diaspora, is still home to the vast, vast majority of Terrans, who live from Mercury in the inner system all the way out to the fringes of the Oort Cloud, all of them part of an extractive machine of capital accumulation that serves a tiny fraction of the whole and immiserates the rest.
Over the last 500 years, industrialization has spread across the system; asteroids are broken up for mining, trace elements are skimmed in vast quantities from the endless reserves of the gas giants, and the Kuiper Belt is a flurry of ships mining cometary ice. Pick any point in the Sol System, and you're likely to find a miserable Terran just waiting for the Affini to come along and rescue them — but there are a few places where most of those adorable little Terrans are likely to be found.
Earth, more often called Terra in the Accord's official media and bureaucracy, is humanity's homeworld. Every human being, no matter where they were born in the galaxy, has a relatively recent ancestor who was born, lived, and died on this little world. For uncountable eons up until relatively recently, every dream, every struggle, and every disaster that humanity experienced took place here.
Earth is not a pleasant place to live unless you're very wealthy; average temperatures are significantly higher than the averages of the Old Climate, before carbon emissions steered the planet out of a glacial minimum and into a full-on warming period. Most tropical zones experience wet-bulb temperatures above the limit for human survival for 150 or more days each year, and are wracked with storms that would have eclipsed any measurement system devised under the Old Climate. Sea levels are nearly 2.5 meters higher than they were prior to the Inundation, and those coastal cities unable or unwilling to construct seawalls have long since been washed away by the tide.
In higher latitudes, survival is a bit easier. Regions with high humidity still need to cope with dangerous wet-bulb temperatures frequently, and so buildings in these areas are usually designed with at least moderate climate control in mind. Most cities still extant at these latitudes (for example, Vancouver-Victoria or Melbourne) are active spaceports, since the lower the latitude, the cheaper the launch to orbit. Only a few extremely wealthy conglomerates, as well as the Cosmic Navy, have the drive and the resources to construct spaceports nearer to the equator, and these are usually heavily reinforced against the weather and boast climate control infrastructure of the kind you'd expect to see on a top-of-the-line starship.
These spaceport cities are usually heavily crowded and just as heavily policed, and are where the majority of jobs are to be found; consequently, over the last two centuries or so, there's been a significant depopulation of outlying areas. Services and support for those who live away from the cities are few and far between, and law enforcement is either completely nonexistent or at the whim of whatever corporation owns the land. Consequently, rural areas are frequently dangerous, and become more so the further one travels from a city as a rule.
As one nears the poles, the climate begins to resemble something closer to what Earth's temperate regions used to experience. Cities built here, like Greater Rejkjavik, Archangelsk, or Anchorage, are often the playgrounds of the wealthy, with shining skyscrapers of glass and broad estates where trillionaires hold court. Those who labor to serve them frequently can afford little more than a sleeper pod and the calories to eke out basic survival. The most polar of these cities, like Longyearbyen, McMurdo Bay, or Alert, house only the wealthiest of the trillionaire class and cater to the handful of the Accord's quadrillionaires when they deign to set foot on Terran soil. Sometimes, thanks to heavily engineered climate infrastructure, snow even falls at these latitudes.
The biosphere of Terra is a mere shadow of what it once was, having been repeatedly decimated by climate collapse, pollution, and escaped designer genomes outcompeting wild strains. In 2550, the planet is still living in the aftermath of the Holocene Extinction Event, most total extinction event since the "Great Dying" of the Permian-Triassic extinction wave — some scholars would argue that it was still ongoing, and that those species that had managed to survive thus far were simply the trailing edge.
No large land animals survive in the wild, and those that survive in captivity are almost universally animals from domesticated species whose utility to humanity kept them alive — and even their numbers are greatly diminished. Domestic canines and felines still exist, but they too are far less common than they used to be. Generally speaking, the probability of a species remaining extant is in direct proportion to its ability to adapt to humanity's presence, because there's very few ecological niches left to occupy in the wild.
Forests are almost unheard of outside the boreal regions of the planet, due to desertification, massive repeated wildfires, clearcutting, and other hazards. Scrub grasses and creeper vines like kudzu dominate, depending on the aridity of the region. Toxic algae blooms are extremely common, rendering most shorelines dead zones (not that pelagic sea life has fared any better, with the sheer amount of plastic particulates drifting in the gyres).
Humanity saw all this coming, though precious little was done to stop it. One shining achievement of pre-collapse humanity was the establishment of seed and genetic banks in formerly remote locations like Svalbard; though several failed due to cut corners or climate disaster, the genetic record of many species has nevertheless been preserved. Unfortunately, those records were usurped by trillionaries and especially, in the Accord Era, quadrillionaires; as a result, even if the will to repopulate Terra's biosphere existed, the information necessary to do so moldered under perpetual copyright.
By 2554, the Affini had arrived in the Sol System, and were ill-disposed to tolerate the present state of affairs. Their first priorities were emergency care, social stability, and especially housing — virtually all Terrans living on the planet did so in appalling conditions and very tight quarters, usually overcrowded to boot with an attendant malus to health and well-being. Using industrial compilers, the Affini quickly saturated every city on the planet with appropriate housing, typically in the form of highrise apartments; convincing Terrans to move into these new apartments, after they'd been relentlessly propagandized by the Accord for years, turned out to be the more difficult end of the project. Still, by the end of the year, housing insecurity was effectively gone and virtually everyone who wasn't actively resisting the Affini had a home they could scarcely have dreamed of and certainly couldn't have afforded under the Accord.
Terra's ecological and climatic status was dire, but the Affini are well practiced at ameliorating even the worst such disasters. They immediately set to work restoring Terra's biosphere, both through climatic infrastructure far more efficient than anything humanity had ever conceived and through a relentless program of genetic refactoring and redesign that restored a great many formerly extinct species to life.
Still, it takes a long time to turn a planet around, even for the Affini, as climates have a tremendous amount of inertia on their side; while lower-latitude cities began to enjoy cooler temperatures and milder weather relatively quickly, and healthy managed greenery and even animal life not long after that, the project to fully reconstruct a self-sustaining pre-collapse biosphere (or as near as can be approximated) is estimated to take anywhere from 80 to 100 local years.
While many students in the Accord's privatized education system learn that the process of colonizing Terra's moon began in 1969 CE, when the capitalist United States of America defeated the communist Soviet Union in the Great Lunar War (also called the Cold War, after the very low average temperature of space), this is not strictly speaking true; for one thing, Luna went more than 70 years without a human setting foot on her following the cancellation of the Apollo program, and real colonization didn't start in earnest for some time thereafter, as the Collapse was rather occupying humanity's attention.
Still, in 2550, Luna is a major industrial and population center, and prior to Mars' terraformation the shining center of humanity's presence in space. The moon's low gravity made it an ideal place to construct and launch new ships, and its orbit still crawls with refineries, habitat stations, and the husks of mined-out metallic asteroids steered inward from the Belt. The surface is festooned with domed cites dug deep into the Lunar regolith; since the moon lacks an active core, it also lacks a magnetic field, and radiation is a serious concern.
Luna's population is roughly 60% transient labor — that is, workers who emigrate to Luna, spend a few years there, then return home or move on elsewhere. However, that leaves 40% who live full-time on Luna, either having chosen to live there or having been debt-trapped in effective indenture (far more common). A further minority within that segment, about 10% of the total population, were actually born on Luna. These 'Lunies' (a term that has since spread in use to describe anyone living on Luna) are some of the most extreme examples of low-gravity developmental adaptation anywhere in the Accord, and are almost always immediately recognizable by their elongated skeletal structure.
Prior to 2550, Luna's economy had been in a decades-long slump. As the industrialization of space continued, and especially as the price of an FTL engine came down, it became much more practical to simply construct ships in space rather than in pieces on the surface, even jumping drydock infrastructure to the larger metallic asteroids rather than relying on the cumbersome process of steering them to Lunar orbit. Luna limped along on transit services, but it was clear the once-prominent moon was in decline; one famous bit of graffiti at Shackleton Spaceport read "Will the last one off Luna please turn out the lights?" Once war with the Affini broke out, however, Luna experienced a short-lived economic boom as old drydocks were quickly spun back up; this boon was a double-edged sword, however, as it also brought with it a heavy Cosmic Navy presence and permanent martial law.
Mars has been continuously inhabited for several hundred years, nearly as long as the slow process of terraforming has been under way, and it's the cultural and social center of the Solar System as far as most Terrans are concerned.
Mars is both smaller than and less dense than Earth, and without an active core it also lacks a magnetic field. This means that, prior to terraforming, the atmosphere was stripped down to the barest traces, and the surface regularly bombarded by unhealthy levels of radiation, making it a real planetary fixer-upper. The first stages of terraforming began over 200 years ago, with baby steps like importing hardy engineered lichens to begin processing the regolith, decreasing the planet's albedo, and thickening the atmosphere. The next stages involved periodic cometary bombardment, adding water to the planet's bare-bones hydrosphere a few cubic kilometers at a time.
Development of practical FTL greatly improved the pace of terraformation. Before, the Kuiper Belt mining program was almost entirely operated by remote, and a single malfunction could set the project back by months. After, a single ship could simply "jump" a Kuiper Belt object fragment in-system to a position where its vector and inertia would naturally carry it right to the red planet's doorstep.
The space boom also made larger space infrastructure possible, perhaps the most ambitious of which was the Mars Geomagnetic Augmentation Array. This facility, positioned at the L1 point between Mars and the Sun, generates an extremely powerful magnetic field that creates a "magnetosheath," diverting solar radiation away from Mars in much the same way that Earth's natural magnetic field does for humanity's homeworld. Little more than a series of reactors, radiators, and a massive superconducting magnet, the MGAA is a maintenance nightmare that experiences periodic variation in efficacy and even total outages (intentional or otherwise), sometimes requiring Martians on the dayside to take shelter from solar weather until repairs can be made. A popular conspiracy theory holds that the Accord actually shuts the MGAA down intentionally to make the surface inhospitable for any large gatherings by nascent political opposition.
Today, the surface of Mars is not only habitable, but even comfortable at times. The average atmospheric pressure at sea level is about 550 millibars, or a little more than half of Earth's sea level air pressure. Temperatures vary significantly, as Mars still has a very low thermal inertia even after terraforming — highs usually top out in the 20s C, but even in the relatively warmer northern hemisphere summer temperatures can drop below freezing at night. Frost is a common sight in the mornings, and only the hardiest crops can be grown on the surface. A great deal of agriculture still takes place under domes or in hydroponics bays underground; both require high-output sunlamps, since sunlight on Mars is significantly less intense than on Earth.
While it still boasts broad stretches of uninhabited desert frequently referred to by locals as the Outback, a loanword from Australian emigrés, the Mariner River Valley region, Xanthe Terra, and the adjacent coastline of the Boreal Sea are as densely populated as anywhere on Earth and include some of humanity's oldest settlements on the planet. This includes the mothballed remnants of Amphora, an early settler habitat dug into the walls of Noctis Labyrinthis that is now host to a museum operated by a small consortium of tourism companies.
Most inhabited spaces are still heavily climate-controlled. Older settlements, dating from the early days when radiation was a constant concern, tend to extend deep underground, with tunnels and chambers dug into the Martian bedrock. More recent construction tends to rely on aerogel domes to maintain a higher atmospheric pressure and temperature than the ambient Martian mean, and the newest settlements — especially the ritzy areas along the Boreal Sea coast and around the Great Hellas Lake — are standalone buildings, either large apartment blocks or homes virtually indistinguishable from those on Earth, with doors opening directly to the Martian environment.
The Martian day (or "sol") is a little under 40 minutes longer than Earth's day, and the Martian year is slightly less than two years long. Prior to 2481, Martians used the Arean Calendar, and accounted for the 40 minute difference with a "zero hour" each night during which clocks paused for the interval. However, with the Accord Timekeeping Standardization Act, for official purposes Mars was required to use Accord Universal Time, which has resulted in significant calendrical drift with regard to the Arean Calendar (which many Martians still privately use).
Beyond Luna, Mars, and the Belt lies uncountable kilometers of open space — and then, on the far side of that yawning chasm of emptiness, lie the great gas giants, Jupiter and Saturn. Spectacular in a way that evolution could never have prepared humanity for, these worlds are where the truly, absurdly wealthy — the quadrillionaires — have carved out their private little kingdoms. The handful of sybarites who collectively own over 90% of material wealth in the Accord spend that money here, on private stations and O'Neill cylinders designed to cater to their specific whims and with a view that anyone would kill for. Prototype ansibles, often more expensive than the stations themselves, keep them connected to the media and economic spheres of Terra and Mars, and private jump-shuttles ferry them back and forth to soirees millions of kilometers distant. Trillionaires consider themselves fortunate to be invited to these places; those below them on the social ladder can but watch carefully tailored vids and dream.
The hyper-wealthy aren't the only ones out here, of course; someone has to do the actual work of keeping the stations running, and there are industrial interests as well, particularly around Titan, whose methane lakes are the Sol System's primary source of petrochemicals now that Terra's fossil-fuels have been largely tapped out. The Saturnian moon's low gravity makes it a favorite out-system destination for Luna-born workers who want a bit of elbow room, since the thick atmosphere shields against radiation enough that dome cities can sprawl instead of digging down.