Terminology and classifications (The Expanse)

This page will explain some terms and classifications that are used in The Expanse scenario. I will also explain some scientific terms like Lagrange points.

Arthur’s Size Classification for Celestial Objects
Arthur’s Size Classification for Celestial Objects, also known as Arthur’s Size Classification or Arthur’s Classification for Celestial Objects is a way of classifying celestial objects by their diameter or length. It was developed in 2105 by the astronomer Cooper Arthur.

Lagrange points
Any object in space that orbits another object creates 5 Lagrange points named after Joseph-Louis Lagrange (https://en.m.wikipedia.org/wiki/Joseph-Louis_Lagrange), an Italian mathematician and astronomer. Lagrange points are stable locations in which the gravity of 2 the objects cancels each other out and any object here will not go further away from either one the objects even though it would normally orbit faster or slower. Lagrange point are named: Lagrange point [Orbited object]-[Orbiting object] [number from 1-5]. Lagrange point 1 is in front of the orbiting object (B) from the perspective of the orbited object (A). Lagrange point 2 is behind B as seen from A. Lagrange point 3 is always on the other side of A as seen from B. Lagrange points 1-3 are metastable, meaning that an object here can still be nudged out of position and begin orbiting A by themselves. Lagrange points 4 and 5 can be found by charting equilateral triangles, 4 is in the direction that B orbits while 5 always chases B. Lagrange points 4 and 5 are stable.

Terraforming
Most people will probably know what terraforming is. But for those that don’t, terraforming, comes from the Latin terra meaning earth or land and the English word forming. So terraforming litteraly means ‘making earth(like)’. It is an incredibly slow process that takes hundreds of years, the terraforming of Mars took 800 years from 2370 all the way to 3170. Mars is the only planet that has been terraformed, though terraforming projects for two other planets are happening and a plan for the terraforming of a third one has been proposed. Most of these will be finished by the year 3600-3800 (with the exception of the third one which will be completed much later, probably around the 4400s).

Another type of terraforming is called paraterraforming, it basically means that you build domes that are like earth, similar to what a lot of people envision the moon, covered in domes that have earth-like conditions, but the rest of the planet is unchanged, most of the time (all of the time in this timeline) before the terraforming process begins, paraterraforming is already well on its way. In theory you could even completely paraterraform a planet, the structure is often called a worldhouse.

There is also aquaforming. This is the adapting of an ocean or ice planet/moon, by use of underwater fusion reactors, to make it inhabitable for marine life.

Asteroid
Almost everyone will know what an asteroid is, but I will still explain it for the few people that don’t. An asteroid is basically a huge rock in space, planetoids are overall larger than asteroids, but both terms can and are used interchangeably. Asteroids can be split up into three major categories: S-type, M-type and C-type. The S-type is mostly made from Silicate, basically rock. The M-type is metallic, mostly nickel and iron, and and finally the C-type has a lot of carbon. Obviously most if not all asteroids are a combination of the three, but if an asteroid is mostly made from one of these it will be classified as one of these. Some asteroids have an almost equal amount of two or even all three of these materials, these are known as SM-type (Silicate and metallic), SC-type (Silicate and Carbon), MC-type (Metallic and Carbon) and finally the SMC-type (silicate, metallic and carbon). But if you just use the original three, than are C-types the most common (70%), S-types are far less common (17%) and lastly M-types are the rarest at just 13%. Most asteroids are named in a basic order, beginning with the name of the star system after that two letters, these come from whatever area around the star the asteroid is found in and after that a number. Only the very biggest of asteroids, like Vesta get independent names.

Some basic abbreviations
Here are some basic abbreviations that are used in the expanse universe.

Orbit classifications
The most common way to classify orbits is by their height. This height, however, is in comparison to the object and therefore the height of the orbit around object A is the radii of object A times X (the number in the column).

Geosynchronous and geostationary orbits
A geosynchronous orbit is an orbit around Terra where the satellite orbits the earth in the same time it takes for Terra to rotate around its axis. A semi-synchronous orbit is an orbit where the satellite orbits the object in half the time it takes for said object to rotate around its axis. A geostationary orbit is a circular geosynchronous orbit above the equator and can be used to place stations for space elevators and the fact that 2 objects in geostationary orbit can never hit each other without some outside force interfering. Whilst both geosynchronous and geostationary orbits originally only referred to orbits around Terra they later began to refer to an orbit around any planet, star, moon or asteroid.

Inclination
Orbits can also be classified by their inclination. There are 3 main types.
 * An inclined orbit is an orbit whose inclination relative to the equator is not 0.
 * A non-inclined orbit is an orbit whose inclination relative to the equator is 0.
 * A near equatorial orbit is an orbit whose inclination relative to the equator is nearly 0.
 * A polar orbit is an orbit whose inclination relative to the equator is either 90° or -90° or very close, meaning that the orbiting object (almost) passes over the poles.

Eccentricity
Orbits can also be classified by their eccentricity (e). Both parabolic and hyperbolic orbits have a velocity equal to (or greater than, when is comes to hyperbolic orbits) the escape velocity, meaning that they will escape the planet.
 * A circular orbit is an orbit with e=0
 * An elliptical orbit is an orbit with 01
 * A parabolic orbit is an orbit with e=1
 * A hyperbolic orbit is an orbit with e>1

Planet vs. dwarf planet
Most people know that the Sol system counts eight planets (Mercury, Venus, Terra, Mars, Jupiter, Saturn, Caelus and Neptune) though originally there was one more: Pluto. Pluto was demoted from a planet to a dwarf planet in 2006. This makes a lot of people ask the question: “What is the difference between a planet and a dwarf planet?“ and I want to quickly give an answer. First of all what is a planet? A planet is an object that orbits a star, not a planet (therefore removing moons), has a roughly spherical shape because of its gravity, otherwise every asteroid and piece of debris orbiting a star would be a planet. And lastly has cleared out its orbit, meaning that no other planets or a large amount of asteroids are in the way. A dwarf planet is in all regards almost the same as a planet, the only difference is that a dwarf planet does not account for the last requirement and since Pluto does not account for the last requirement, therefore it is a dwarf planet.