GUIDE TO THE UNITED NATIONS SPACE AUTHORITY STANDARDIZATION OF DESIGNATIONS OF CELESTIAL BODIES AND ARTIFICIAL CONSTRUCTS ACT OF 2204: SECTION 3
Note: The word world in use for this act is defined as any object created naturally that is independent from physical connections to any other objects that do not naturally initiate fusion or used to naturally initiate fusion and is not a Black Hole. Technically, this includes everything from microscopic specs of dust to planets many times the size of Jupiter, just barely not Brown Dwarfs.
Note: The difference between a Space Habitat made from an Asteroid and a settled Asteroid can be vague, with any dividing line being arbitrary. For the purpose of this act, the dividing point is when over 50% of the Asteroid is used for the benefit of the Habitat or is material of the Habitat.
Terrestrial Worlds are classified into three categories, each with three tiers within them. In each category, the worlds are rated by separate criteria and then placed into their tier.
Uninhabitable Worlds have little to no properties that would make them a more enticing settlement than a Space Habitat. This includes dust, asteroids, comets, and some moons. They are usually only used for resource extraction and sometimes for construction, like turning an asteroid into a Space Station or Habitat, though some of the bodies in this category are used as isolated communities or mining command bases, holding the workers who command the robots on other asteroids. Represented by a U in classification.
Tier 1: Meteoroids. Useless for anything but resource extraction or ammunition.
Tier 2: Asteroids of a relatively small size (a meter to a few dozen meters). They are used for resource extraction as they are too small for anything else.
Tier 3: Larger asteroids (hundreds of meters to hundreds of kilometers), moons, comets, dwarf planets, and some planets. Used for resource extraction, but also commonly turned into Space Stations, mining command bases, mining hubs, and colonized by isolationist communities. They usually have only a small amount of gravity, less than a tenth of a G, so inhabitants need a supplementary gravity source or a large amount of physical activity to remain healthy. Good examples of Tier 3 worlds are Ceres, Juno, and Mercury.
Habitable Worlds have some properties that make them good for colonization but are not considered Garden Worlds. Unlike Uninhabitable Worlds, which are only rated by size, Habitable Worlds are rated based on many factors like gravity, surface temperature, atmosphere, magnetic field, radiation, and many more. These worlds can not be inhabited by baseline humans but can be inhabited by humans with technological assistance or sufficient augmentations. Represented by an H in classification.
Tier 4: Barely habitable; these worlds only have a few of the characteristics of a habitable world. A good example of the Tier 4 world is Venus, a thick but harmful atmosphere, a gravity close to Earth's but no magnetic field, and a thoroughly unpleasant surface.
Tier 5: habitable; these worlds have most of what is needed for Earth-like life. These worlds usually don't have a breathable atmosphere but do have a thick atmosphere, a large amount of water, and/or several other conditions required for habitation and even life. It is not uncommon for these worlds to have simple life to exist on these worlds, and they have the potential to become Garden Worlds if left alone over eons, if of a different type from Earth in some cases.
Tier 6: Take Earth, then remove the life. Tier 6 worlds are anomalies, so hospitable to Earth-like life yet so lacking in it. They are far better colonization locations than many Tier 7 and even 8 worlds. Tier 6 worlds are the only habitable worlds that are economical to fully terraform. These worlds are extremely rare, rarer than even Tier 8 Garden Worlds. The most famous is Noah, a Tier 6 world that was terraformed with Earth plants and animals and then quarantined as a preservation with only researchers allowed; an entire world turned into a copy of Earth's ecosystem before humanity.
Garden Worlds have complex life already on them, from primitive plants to entire ecosystems even older than Earth's by eons. Represented by a G in designation.
Tier 7: Worlds without fully developed ecosphere, they have primitive life, but it is young. Most Tier 7 worlds lack land animals. These worlds are commonly terraformed, turning the time it takes for the world to become Tier 8 worlds from millions of years to dozens or hundreds. A good example of a Tier 7 world was Alexandria, a world in the Alpha Centauri System that was once a Tier 7 world. When humanity reached the system, the world only had simple life, bacteria, plants, and a few early land animals. Over the course of two centuries, the world was turned into a Tier 8 Garden World. It is one of the great wonders of human space, the first terraformed world, a paradise made by human hands.
Some of these worlds used to have more sophisticated ecosystems, but they were destroyed in the past.
Tier 8: Worlds with a full planetary ecosphere like Earth. These are usually prime targets for colonization, but not always. Not all ecospheres are like Earth, some are vastly different, and that can cause trouble.
An example of this is Ceridwen, a Tier 8 Garden World only 11 light years from Ymir. The world orbits a F-type star in a very elliptical orbit, leading to seasonal changes that are almost apocalyptic. At its farthest point from the star, even the warmest places on the world are similar to antarctica, at its closest point the coldest point is twice the highest recorded heat on Earth. This has lead to an extremely odd ecosphere, most of the world is hibernating at one time or another, usually under the surface or in the deep ocean. Only a few colonists settled on this world, exploiting the seasonal changes to extract a large amount of solar power in the summer, storing it to power mining, refining, and manufacturing operations in the winter, exploiting the low temperatures for more efficiency.
Tier 9: Old worlds, old when the first species evolved on Earth, some even old when their was no Earth, or even Sol. Some of these worlds continue to flourish, surviving through catastrophe after catastrophe for eternity to this day, monuments to the power of life, but most have faltered over the eons, their bright light in the cold darkness of the universe withering and finally going out, a grim reminder to the enemy of all life, time.
Those that have fallen, those post-Garden Worlds, can be reclaimed, the power of terraforming resurrecting these worlds, if it is worth it. These worlds orbit old, low metalicity stars, nearly worthless besides the life they sometimes hold. Few have survived with life remaining; over such stretches of time the very worlds start to die, their molten, powerful cores cooling to husks, their rotations slowing over eternity or even stopping.
A few of these worlds live to this day, and they are cherished for the pools of near-endless knowledge that can be learned from them. One of these worlds is Genesis. Orbiting an old K-type star 100 light years from Sol, Genesis is the only terrestrial world of the 5 planets in the system. Life has existed on Genesis five times as long as Earth; life was living on the world before even Sol came to be. Genesis is dying and has been for eons. Its life has fought and changed to survive, but it will not last forever. Humanity has tried to help, but even humanity knows its limits. Whether humanity's actions can somehow save the planet, delay the inevitable, do nothing, or even make it worse is not known, but humanity will try.
Habitability Score: Habitable and Garden Worlds are scored on their habitability as a whole for humans on a one to nine scale, one being the least habitable and nine being the most. This score is put as a decimal after the Tier.
Size Score: Uninhabitable Worlds are rated on size from one to nine, with nine being the biggest, while one is the smallest, going like this:
1: Sub one kilogram
2: Sub 1 kiloton
3: Sub 1 megaton
4: Sub 1 gigaton
5: Sub 1 Teraton
6: Sub 1 Petaton
7: Sub 1 Zettaton
8: Sub 20 Zetatons
9: Sub 1 Yottaton