- Being physically based. Class name must reveal the most important properties of a planet: it's size, bulk composition, surface conditions.
- Must describe all known planet types and theoretical ones, like carbon and chthonic planets.
- Being descriptive. No abstract Star Trek-style classes M, F, G etc. Class name must immediately give the user information about the basic nature of a planet. I mean that it must be a set of words, like in the current SE classification: "temperate terra with life".
- But the description also cannot be too long.
- Class names must be single-word. One can use "very hot" instead of "scorched", but we must try to avoid this, to reduce confusion and makes description more compact.
- Class names must have a scientific style. I.e. using Latin/Greek prefixes "hypo-", "meso-", "cryo-" is a good choice. Also, "terra", "selena" etc.
There are several alternate classification schemes which we have developed, and I started to implement some of them in the code. I hope your suggestions in this thread will help us to select the best one. It is very important to make this classification readable and nice-sounding in other languages. So if you are not an English speaker, try to translate the classnames in your mind, and write here if you find some issues. We shall try to change words/scheme to satisfy all languages. At least to avoid ridiculous combinations
So the planet description is made by combining several class names:
- temperature class
- atmosphere class (atmosphere pressure + breathability)
- surface volatiles class (volatiles composition, amount and physical state)
- surface bedrock composition class
- size class
- bulk composition class
- additional info (tidal locked, life etc)
Some classes could be skipped entirely, to make the description more compact. Example layouts:
"temp_class atmo_class [additional] volatiles_class surface_class size_class bulk_class".
Earth: "temperate mesobaric inhabited marine rocky terra"
Mars: "cool hypobaric hypoglacial rocky subterra"
Titan: "frigid mesobaric cryolaky icy subaquaria"
"temp_class volatiles_class surface_class size_class bulk_class [additional]".
Earth: "temperate marine rocky terra with life"
Mars: "cool hypoglacial rocky subterra"
Titan: "frigid mesobaric cryolaky icy subaquaria"
"temp_class surface_class size_class bulk_class [with volatiles_class] [with/and additional]".
Earth: "temperate rocky terra with water seas and life"
Mars: "cool rocky subterra with CO[sub]2[/sub] glaciers"
Titan: "frigid icy subaquaria with hydrocarbon lakes"
First, I'll describe the bulk and size classes, because they are the most important.
Bulk class
Describes the bulk composition of a planet, i.e. the major substance forming the planet.
terra - rocky planet (combined old terra, desert and selena classes)
aquaria - water/ice planet (combined old oceania, ice world and titan classes)
carbonia - carbon/carbid/diamond planet (new class, hypothetical carbon-dominated planet)
ferria - iron/metal planet (new class, hypothetical)
neptune - ice giant planet
jupiter - gas giant planet
chthonia - core of an evaporated ice/gas giant, or a helium-rich giant (not sure about this class)
asteroid - for asteroids, comets and dwarf moons (irregularly-shaped small bodies)
The terra class could use the alternate class name earth. The reason for this is making classification closer to modern astronomy. In SE you sometimes visit a large terrestrial planets, which will be called "superearth" - matching the astronomical term (see below).
The aquaria class could use the alternate class name: oceania or glacia/cryogenia, depending on temperature. Because frozen oceania (= ice world) will sound strange, as will warm glacia (molten, = oceania). But this is not a very good solution, because it adds messiness to the classification, and also some uncertainty exists: imagine a tidally locked planet, which have a global water ocean on a day side and a global ice glacier on a night side (TRAPPIST-1 f). What would you call it, oceania or glacia? Also, "glacia" does not have a good translation to Russian.
The ferria class could use alternate names: ironia, metallica, but they sound funny
Also, ferrum in Latin means "iron" - I think it is suitable class name, to continue the pattern (terra - ground, aqua - water, carbo - coal).The neptune and jupiter classes alternatively could be named "ice giant" and "gas giant". But it has two drawbacks: first, it makes a double-word class name, which I want to avoid (like getting rid of old "ice world" class). This also makes some trouble with adding a size class prefix (see below). Second, using the word "neptune" removes annoying questions like "how can an ice giant be hot". Also, "neptune" and "jupiter" are commonly used class names in modern astronomy.
By the way, I made an option to switch between these alternate class names for developing and debug usage. I simply can leave it in the release as a config file parameter or even a switch in the settings menu. So you could switch "jupiter" back to "gas giant" if you like.
Size class
It is proposed as a simple prefix to the bulk class:
mega - huge
super - big
(no prefix) - normal
sub - small
mini - little
micro - tiny
Examples: superterra, subaquaria, minineptune.
More specifically, this is a mass class, not size. Because mass is more important, it defines how match matter forms the planet; size (radius) depends not only on mass, but also on chemical (bulk) composition.
Possible subdivision between classes for solid planets, in Earth masses:
<2*10[sup]-6[/sup] (micro), 2*10[sup]-6[/sup]-0.0002 (mini), 0.0002-0.02 (sub), 0.02-2 (no prefix), 2-20 (super), >20 (mega)
<2*10[sup]-6[/sup] (micro), 2*10[sup]-6[/sup]-0.0002 (mini), 0.0002-0.02 (sub), 0.02-2 (no prefix), 2-10 (super), >10 (mega) - more corresponds to a scientific definition of superearth (2-20 Earth masses)
Alternate, "natural" (logarithmic). Earth in this system will be "superterra", not very nice... Shifting it by a factor of 2 is better.
<0.0001 (micro), 0.0001-0.001 (mini), 0.001-0.01 (sub), 0.01-0.1 (no prefix), 0.1-1 (super), >1 (mega)
Examples:
Kepler-10b - superterra (superearth)
Kepler-10c - megaterra? (17 Earth masses)
Earth, Venus - terra
Mars - terra (because it is > 0.02 Earth masses)
Mercury - ferria (it has an iron core 60% by mass, the whole planet is also > 0.02 Earth masses)
Moon, Io - subterra (they are < 0.02 Earth masses)
Ceres - miniterra (Ceres is rocky, it has ice as a relatively thin mantle, 25% by mass)
Europa - subterra (it is also a rocky world, the ice and subsurface water ocean is just 10% of its mass)
Ganymede, Titan - aquaria (they are by 50% composed of water, and also fall into the "no prefix" class due to mass > 0.02 Earth masses)
Callisto - subaquaria (it is < 0.02 Earth masses)
Gas giants (jupiters) must use a different scale. Possible subdivision in Earth masses:
<6 (mini), 6-60 (sub), 60-600 (no prefix), >600 (super)
The same in Jupiter masses:
<0.02 (mini), 0.02-0.2 (sub), 0.2-2 (no prefix), >2 (super)
For ice giants (neptunes), I'm not sure about the subdivision. One possible way (in Earth masses):
6-10 (sub), 10-40 (no prefix), >40 (super)
The same in Jupiter masses:
0.02-0.03 (sub), 0.03-0.13 (no prefix), >0.13 (super)
6 Earth masses is the theoretical subdivision limit between rocky planets and planets with a large gaseous atmosphere (so-called mini-neptunes), so is a good choice for the classification. But in our classification they must be called sub-neptunes, to save the "sub - (no prefix) - super" scheme. Super-neptunes are very rare transitional planets with a mass of ~60 Earth masses, similar to those of a very lightweight gas giants, but still not having the metallic hydrogen layer. Presence of metallic hydrogen is a natural physical criteria to distinguish "true" gas giants from other planets.
An example of a mini-neptune (or subneptune in our scheme) is Kepler-11f: 2.3 Mearth and 2.6 Rearth. It could be classified as a superearth or superaquaria with a large atmosphere though, so subneptune class could be omitted. Subdivision line between aquaria (icy/water planet) and neptune (icy planet with a H/He atmosphere) is not very sharp. Considering this, one could exclude the ice giants class at all - they are the same as "mega-aquaria" (>10 or >20 Mearth). But "ice giant/neptune" is the commonly used term in astronomy...
Alternatively, ice and gas giants could be merged into a single "giant" class. Then we could use this scheme (in Earth masses):
<6 (mini), 6-60 (sub), 60-600 (no prefix), >600 (super)
or the same in Jupiter masses:
<0.02 (mini), 0.02-0.2 (sub), 0.2-2 (no prefix), >2 (super)
This scaleis beautifully monotonic, but not physically-based. We omitted the criterion of the presence of metallic hydrogen. Use this for "true" gas giants only, and merge neptunes with aquaria?
Asteroids should use either different size scheme, or even omit it (call them just "asteroid", not depending on size/mass). HarbingerDawn proposed to use the same class names as for terrestrial planets for a large asteroids with differentiated interiors (thus Vesta will be microterra), and call other asteroids "asteroid" (without size class). In my system, asteroids are bodies with irregular shape smaller than 300 km (rocky) or 200 km (icy).
Temperature class
Describes temperature on a planet's surface, or equilibrium temperature for gas giants. Could be changed to equilibrium temperature for all planets, but this will make Venus and Earth in the cool class...
scorched - hot - warm - temperate - cool - cold - frozen (like in SE now)
scorched - hot - warm - temperate - cool - cold - cryogenic (like in the SE translation to Russian now)
torrid - hot - warm - temperate - cool - cold - frigid (HarbingerDawn's proposal, but the word "frigid" has a ridiculous translation to Russian)
very hot - hot - warm - temperate - cool - cold - very cold (satisfies Russian language, and removes the word "cryogenic", which could conflict with other class names; but I want to avoid double words in the class name)
The temperature ranges which are used in SE now are:
>800K (scorched), 800-400K (hot), 400-300K (warm), 300-250K (temperate), 250-200K (cool), 200-100K (cold), 100K-0K (frozen)
Atmosphere pressure class
Describes the pressure range of the atmosphere. This class name is not used for gas giants, because they all will be ultrabaric/megabaric.
airless - infrabaric - hypobaric - mesobaric - hyperbaric - ultrabaric
Proposed pressure range (in atmospheres/bars):
0-10[sup]-6[/sup] (airless) - 10[sup]-6[/sup]-10[sup]-3[/sup] (infrabaric) - 10[sup]-3[/sup]-10[sup]-1[/sup] (hypobaric) - 10[sup]-1[/sup]-10[sup]1[/sup] (mesobaric) - 10[sup]1[/sup]-10[sup]3[/sup] (hyperbaric) - >10[sup]3[/sup] (ultrabaric)
Thus Venus would be hyperbaric, Earth - mesobaric, Mars - hypobaric, Pluto - infrabaric.
Another interesting option is using the metric system prefixes to describe the atmospheric pressure: milli-, kilo- etc:
airless - nanobaric - microbaric - millibaric - centibaric - decibaric - unibaric - decabaric - hectobaric - kilobaric - megabaric
10[sup]-9[/sup]-10[sup]-6[/sup] (nanobaric) - 10[sup]-6[/sup]-0.001 (microbaric) - 0.001-0.01 (millibaric) - 0.01-0.1 (centibaric) - 0.1-1 (decibaric) - 1-10 (unibaric) - 10-100 (decabaric) - 100-1000 (hectobaric) - 1000-10[sup]6[/sup] (kilobaric) - >10[sup]6[/sup] (megabaric)
But this system has some problems. First is using exact "1.0" borders makes Earth with 1.0 atm pressure - unibaric, but a planet with 0.999 atm pressure - decibaric (because its atmospheric pressure is 9.99 decibars). Second is it produces too many classes. One can skip centi-, deci-, deca- and hecto-, but then the first problem became even worse: if Earth is unibaric, then planet with 0.999 atm will be millibaric (999 millibars).
We decided to remove the atmo pressure class from the description, to make it more compact (see below).
Atmosphere breathability class
We did not consider this much. If we were going to remove the atmo pressure class, this would be useless anyway.
toxic - unbreathable - breathable - bio-hazardous
Additional info
tidally-locked - volcanic - cryovolcanic - cometary - inhabited
Some planets could have these subclasses, some could not, depending on a planet properties. They also could be combined, for example "tidally-locked cometary jupiter" (evaporating planet). But this is not a good way, because it generates double-wording again. The class "inhabited" could be used here instead of a suffix "with life" in the end of description, like in SE 0.9.8.0.
Volatiles class
This is a double/triple-word class, describing volatiles (liquids) composition, their amount and state, which could be combined into a single word. Volatiles are substances which are in liquid form on a planetary surface - forming lakes, seas and oceans, or in a partially frozen form - forming glaciers, which still could evaporate (like water glaciers on Earth, carbon dioxide on Mars and nitrogen on Pluto). This class name is not used for gas giants.
Volatiles composition
lava/magma - water - carbon dioxide/CO[sub]2[/sub] - ammonia - methane/hydrocarbons - nitrogen (countless of them... some planets could have multiple volatiles, which makes this system too difficult)
pyro - thermo - (none) - hypo - cryo (more simple option, describing only the temperature range of a liquid; see examples below)
Volatiles amount
desertic/arid - laky - marine - oceanic
desertic/arid - laky - marine - oceanic - superoceanic (for a planets with a global 100 km deep ocean)
desertic/arid - laky - marine - oceanic - superoceanic - glacial (for a planets with glaciers, for example Pluto has nitrogen glaciers)
If we are decided to omit the atmosphere class, we could add the "airless" here as a volatiles amount class. Airless bodies couldn't have liquids on their surfaces, so always will be "desertic". They could have glaciers though...
Examples:
Venus - desertic terra (so simple
)Earth - water-marine terra / (none-)marine terra
Moon - airless subterra
Mars - CO[sub]2[/sub]-glacial + water-glacial terra / hypoglacial terra (as you can see, the first option is too messy)
Io - magma-laky subterra / pyrolaky subterra (Io has lava lakes)
Titan - hydrocarbons-laky aquaria / cryolaky aquaria (first option is not very precise, because Titan's lakes are composed of hydrocarbons and liquid nitrogen)
Pluto - nitrogen-glacial + CO-glacial subaquaria / cryoglacial subaquaria
Kepler-10b - magma-oceanic superterra / pyrooceanic superterra (example of a molten planet)
Alternate scheme (HarbingerDawn): add a description "with xxx" to the end of a planet class.
Volatiles composition:
lava/magma - water - carbon dioxide - ammonia - methane/hydrocarbons - nitrogen
Volatiles amount:
lakes - seas - oceans
lakes - seas - oceans - glaciers (combined with volatiles state)
Volatiles state:
liquid - glacial
Examples:
Earth - terra with water seas / terra with liquid water
Mars - terra with CO[sub]2[/sub] glaciers and water glaciers / terra with glacial CO[sub]2[/sub] and glacial water (oh... we probably must left only CO[sub]2[/sub] description - as the most prominent volatile on Martian surface)
Io - subterra with magma lakes / subterra with liquid magma
Titan - aquaria with hydrocarbons lakes / aquaria with liquid hydrocarbons
Pluto - subaquaria with nitrogen glaciers / subaquaria with glacial nitrogen
Kepler-10b - superterra with magma oceans / superterra with liquid magma
Surface class
Describes the main bedrock substance. Is not used for gas giants.
metallic - rocky - carbid - icy - watery
Examples:
Earth - rocky terra
snowball Earth - rocky terra
Europa - icy subterra
Hypothetical ocean planet - watery aquaria / watery terra (depending on its bulk composition)
Hypothetical carbon planet - carbid carbonia (carbon planet are theorized to have rocks made of carid instead of silicates)
Hypothetical metal planet - metallic ferria
