Planetary Classification

As humanity spread throughout the galaxy, they encountered a great number of planets with a variety of compositions, surface features, and habitability standards. Names and designations sufficed for a time, but the further categorization based on their natures was created later to simplify things.
== Stellar Criteria ==
Due to the vast differences in the luminosity, surface temperature, mass, and lifespan of the largest and smallest stars, only some of them are capable of harboring life as we know it, with a complexity we as humans would find familiar. 
=== Small Stars ===
Brown dwarf stars of classes L, T, and Y, are not capable of hosting habitable planets as they do not have habitable zones. 
Class M red dwarf stars are small, relatively cool, long-lived, and very common. While capable of hosting life-supporting planets, they are not ideal for this purpose because their planets are often very close to the surface of the star. With a minimum habitable zone radius of 0.04 AU and a maximum of 0.3 AU, depending on the mass of the star, they are often tidally locked. This creates an extreme difference in the temperature of the arid and barren sunward side and the frozen spaceward side, leaving a band of temperate land around the terminator. In addition, they tend to be very violent, with many massive solar flares occurring regularly. Any planets close enough to be within the habitable zone of the star will often be bathed in solar radiation, sterilizing its surface. As the universe approaches heat death, these may become the last refuge for whatever sapient life or life-like entities still exist, as they are capable of burning their small amounts of fuel over the course of not billions, but trillions of years. 
=== Middle Main Sequence Stars ===
Class K stars, or orange main sequence stars, as the second most common class of star in the universe and having long lifespans of between 20 and 35 billion years, are often the first places that are surveyed for habitable worlds. They are not as violent as M-type stars, nor do they have the same risk of tidally locking their local worlds. At the low end, they have a habitable zone ranging from 0.2 astronomical units at the absolute closest to the smallest stars of its type, around half of the mass of Sol. At the high end, the habitable zone ends at 1.0 astronomical unit at the farthest from the largest K-type stars, of roughly 80% of the mass of Sol. 
Class G yellow main sequence stars are known to be capable of supporting life, with the human homeworld of Earth, the authiik homeworld of Udyana, and the neyanta population center of Prrkane all orbiting G-class stars of varying sizes. They have a lifespan of approximately 10 billion years. At the low end, roughly 85% of the mass of Sol, the habitable zone begins at 0.6 Au, and at the high end of 1.15 solar masses, the habitable zone ends at 2.35 AU. They are considered the most comfortable systems for human habitation due to their white or near-white color and relatively standard year lengths for habitable planets, most orbiting their stars in periods ranging between 9 and 30 months. 
Class F yellow-white main sequence stars of 1.1 to 1.4 sols are similar in color to the G stars, but are far brighter and emit many times more ultraviolet radiation and have a lifespan of less than five billion years. As a result, their habitable zone ranges from 1 to 3.2 AU depending on its exact mass. Life on planets orbiting these stars could exist underground or in the ocean given a plentiful ozone layer, as the Bomure did early in their history. For colonization purposes, artificial radiation shielding could be constructed around colony sites, and radiation resistant clothing could be issued as an additional precaution should one be found without shielding for brief periods of time. 
=== Upper Main Sequence Stars ===
A, B, and O type stars are considered too hot, bright, and ionizing for any life to form around them, and tend to die quickly. A type stars of masses 1.5 to 2 times Sol's mass might only live for one billion years, while a B type star of 2 to 16 solar masses might only last 100 million years, and the largest O-type stars of 16 to 100 times Sol's mass might only last for as little as ten million years. This is simply not enough time for complex life to evolve, and in addition, these stars emit massive amounts of ionizing radiation that planets orbiting them, if they were even able to form at all in the case of B and O stars, would be bathed in from the moment they were formed from the dust. 
=== Giant Stars ===
Giant stars are also considered unsuitable for habitation due to their immense luminosity and size, which will have destroyed many of the planets that might have been habitable before, and unless circumstances are perfect, this will not cause any outer planets to become habitable. 
== Terrestrial Grid ==
The current tag used to classify habitable planets is based on four categories, producing a ten-digit number known as a Habgrid ID that can be used to gain an understanding of a planet's surface conditions.
=== Atmosphere ===
The first digit of the hab-id is for the atmosphere type, assigned a value of zero through five based upon its suitability for human habitation. For instance, a score of 1 denotes an atmosphere between 0.7 and 1.5 Earth atmospheres with one part oxygen gas and four parts nitrogen gas, with a small margin for trace other gases. Points are added for higher or lower than normal atmospheric pressures, toxic gases, or poorly proportioned gases.
A "Type 0" atmosphere is similar to that of Mars before it was terraformed, an incredibly thin or nonexistent and unbreathable atmosphere that traps little to no heat, and provides no protection from solar radiation or meteorites.
Type 1 atmospheres are ideal, and are the most similar to that of Earth. A near 1 bar nitrogen/oxygen mixture with room for gases that are not toxic in trace amounts for long periods of time.
Type 2 atmospheres can support humans in both forms without the use of rebreathers or pressure suits, either having a mixture of oxygen or another nontoxic gas at around 1 bar, or a low-pressure atmosphere with the correct partial pressure for human habitation.
Type 3 atmospheres are of adequate pressure, but cannot be breathed by humans. Rebreather equipment is required for outdoor activity.
Type 4 atmospheres are both unbreathable and are outside comfortable pressures.
Type 5 atmospheres are incredibly dense, and prevent any EVA activity on their planet's surfaces.
Name	Description 	Examples
T0 	Atmospheric pressure too low to sustain humanlike life, no matter the composition 	Mercury, Luna
T1 	An approximate 4:1 ratio of nitrogen and oxygen at between 0.7 and 1.3 bar. 	Earth, Mars, Revant
T2a 	An approximate 4:1 ratio of any other inert gas and oxygen at between 0.7 and 1.5 bar. 	Yaart
T2b 	A nitrogen/oxygen atmosphere with .2 bar of partial oxygen pressure, an overall pressure of .2 bar to 0.7 bar or 1.3 bar to 3 bar, and no other human-toxic gases.	Clesti
T3 	Any non-breathable atmosphere of 0.7 and 1.5 bar, necessitating breathing equipment, but not pressure suits for untrained individuals. 	Titan
T4 	Any non-breathable atmosphere of .2 bar to 0.7 bar or 1.5 bar to 3 bar. 	Callia
T5 	A non-breathable atmosphere of above 3 bar. Human activity is not recommended. 	Oneri
=== Surface Gravity ===
Surface gravity, in Habgrid ID, is noted as a percentage of Earth's gravity. Mars' is a 037, while Earth's is a 100 and Clesti's is a 122. This is not represented on the traditional two-axis grid. Three-axis grids have been designed to represent them, but the mathematics behind their representation of planetary surface gravity is questionable at best.
Typically, a score position of 50 represents a value of 100. Each score position below 50 represents a gravitational decrease of 2%, while each position above 50 represents an increase of 10%. A score of 0 represents a lack of gravity, while a score of 100 represents a surface gravity of six gees.
Position	Gravity in Gees	Gravity in m/s2
G-000 	0 	0
G-010 	0.2 	1.961
G-020 	0.4 	3.923
G-030 	0.6 	5.884
G-040 	0.8 	7.845
G-050 	1 	9.807
G-060 	2 	19.61
G-070 	3 	29.42
G-080 	4 	39.23
G-090 	5 	49.03
G-100 	6 	58.84
=== T-O Grid ===
The T-O grid chart was created to track the relationship between average surface temperature and global ocean/sea ice coverage. Both numbers range from 0 to 100, with the first being temperature.
The vertical axis of the chart is temperature, with 0 degrees Celsius resting at the center, a score of 050. Every point gained or lost is a single degree above or below 0. Earth's temperature score before its loss at the hands of Mars in the third interplanetary civil war would have been a 065, but it currently rests at a 059. Mars' score is 040, and the frigid colony of Rece scores a dismal 018.
The second is self explanatory, as a percentage of the planet's surface that is covered by its oceans, including any sea ice, but not continental ice. Earth scores a 073, and Mars scores a 048.
Examples of full scores include...
* Earth: 1-100-059-073
* Mars: 1-037-040-048
* Rece: 1-088-018-013
== Classes by Surface Conditions ==
Class Name 	Initial	Description 	Example
Terrestrial	Te 	Applies to the habitability grid. Liquid water oceans and a breathable atmosphere that supports an ecosphere of plants and animals. 	Earth, Mars, Yaart
Titanean 	Ti 	Similar to a terrestrial environment, but in a much colder temperature range. An icy crust with a mantle of liquid water, thick nitrogen based atmospheres, cryovolcanoes, and oceans of hydrocarbons are features found on this class of world.	Titan
Oceanic 	O 	Found on the far right side of habitability grid, ranging from over 90% ocean coverage to complete cover dozens or even hundreds of kilometers deep. A breathable atmosphere is sometimes seen, but not required. 	Callia
Frozen 	F 	An Oceanic or Terrestrial planet outside the liquid water zone of its star. Atmospheres are sometimes found, but are usually frozen to the surface. 	Ceres, Europa, Enceladus
Barren 	B 	Barren planets feature no surface water and are usually found with a negligible or thin atmosphere and riddled with craters. 	Mercury, Luna, Vegran
Molten 	M 	A planet with a surface partially or completely made from molten lava. 	Dzun
Gas Giant 	G 	A large planet mostly comprised of hydrogen, helium, and other light gasses. 	Jupiter, Saturn, Lambda Prime
Ice Giant 	I 	A gas planet with a high concentration of heavy gasses like methane or nitrogen. 	Uranus, Neptune, Icari
== Classes by Mass ==
Name 	Mass
Sub-Earth 	<0.5 Earth Masses
Terrestrial 	0.5 - 2 EM
Super-Earth
Mini-Neptune	2 - 10 EM
Neptunian 	10 - 30 EM
Saturnian 	30 - 160 EM
0.1 - 0.5 Jupiter Masses
Jovian 	0.5 - 2 JM
Super-Jupiter 	2 - 13 JM
Substellar Object	13 - 78 JM
== Classes by Orbit ==
Name 	Description
Major Planet	A body that A: orbits a star, B: is rounded by its own gravity, C: makes up the majority of the mas near its orbital path.
Minor Planet	A body that orbits a star, but is not classified as a planet. Includes dwarf planets, asteroids, comets, and other small bodies.
Dwarf Planet	A body that orbits a star and is rounded by its own gravity, but has not cleared its orbit of other bodies of a similar mass.
Small Body 	Any small object that orbits a star, but is not rounded by its own gravity or shares its orbit with other, similar bodies.
Moon 	A substellar body that orbits another, much more massive substellar body.
Comet 	An icy object that follows a highly elliptical path bringing it close to a star, causing significant outgassing which creates a vibrant "tail".
Asteroid 	A small body that is not classified as a comet.
Circumbinary	A planet or moon that orbits two parent bodies.
Binary 	A pair of bodies of similar mass that orbit one another.
Trojans 	A pair of bodies that orbit in each other's L4 and L5 Lagrange points.
Rogue 	A planetary mass body that does not orbit a star.
Category:Categorization