Astronomical Object Classification System

The **Astronomical Object Classification System** is the most prominent classification system of astronomical objects in the universe. The Astronomical Object Classification System is primarily used to classify all sorts of astronomical objects such as planets, moons, meteors and many more.

## **Planets and Moons**

### **Bulk Classification**

Describes the bulk composition of a planet or a moon, i.e. the major substance forming the world. These classifications are not at all based on the surface conditions of the world.

* Ferria: World with the majority of its composition made of iron.
* Terra: A world with the majority of its mass in silicates, and usually some iron.
* Carbonia: World with the majority of its composition made of carbon.
* Aquaria: World with a significant portion of it's mass being water or water-ice.
* Cthonia: The core of a jovia or a neptunia that has been stripped of it's atmosphere in a process called a hydrodynamic escape.
* Jovia: Gaseous world with the majority of its mass in the form of hydrogen and helium.
* Neptunia: Gaseous world with a significant fraction of its mass made of hydrogen, and another fraction made of volatiles like Water.

#### **Terra Classification**

Terrae are split into four classes (numbered using letters) according to their surface conditions.

* Class D: Worlds that have a surface consistency similar to deserts, and are usually devoid of any water.
* Class M: Worlds that resemble Earth in appearance.
* Class S: Lifeless worlds with extremely rarified atmospheres
* Class H: Worlds that are covered mostly or entirely by lava.

#### **Aquaria Classification**

* Class I: Worlds that consist largely of volatile ices, such as water ice, ammonia ice, dry ice(CO2) and methane ice.
* Class T: Worlds that have a high amount of rocky material, water ice and organic compounds along with hydrocarbons in their mass.
* Class O: Worlds that are mostly or entirely composed of water.

#### **Jovian Classification**

Jovians are split into five classes (numbered using Roman numerals) according to their modeled physical atmospheric properties.

* Class I: Jovians in this class have appearances dominated by ammonia clouds. These worlds are found in the outer regions of a planetary system. They exist at temperatures less than about 150 K.
* Class II: Jovians in class II are too warm to form ammonia clouds: instead their clouds are made up of water vapor. These characteristics are typical for worlds with temperatures below 250 K. Even though the clouds on such a world are similar to those of terrae, the atmosphere consists mainly of hydrogen and hydrogen-rich molecules such as methane.
* Class III: Jovians with equilibrium temperatures between 350 K and 800 K do not form global cloud cover, because they lack suitable chemicals in the atmosphere to form clouds. These planets appear as featureless blue globes because of Rayleigh scattering and absorption by methane in their atmospheres.
* Class IV: Above 900 K, carbon monoxide - rather than methane - becomes the dominant carbon-carrying molecule in a Jovians atmosphere. These worlds form cloud decks of silicates and iron deep in their atmospheres.
* Class V: For the very hottest of Jovians, with temperatures above 900 K the silicate and iron cloud decks are predicted to lie high up in the atmosphere.
* Class VI: Jovians that have lost most or all of their hydrogen and have a primarily helium atmosphere.

### **Size Classification**

Size classification between classes for solid worlds, in Earth masses:

* <2\*10-6 (micro)
* 2\*10-6-0.0002 (mini)
* 0.0002-0.20 (sub)
* 0.20-2 (no prefix)
* 2-10 (super)
* >10 (mega)

Size classification between classes for Jovians, in Jupiter masses:

* <0.02 (mini)
* 0.02-0.2 (sub)
* 0.2-2 (no prefix)
* >2 (super)

Size classification between classes for Neptunians, in Earth masses:

* <6 (mini)
* <6-10 (sub)
* 10-40 (no prefix)
* >40 (super)

## **Habitability Classification**

Astronomical objects are classified by their habitability into six distinct classes. This class is only used when one of the criteria below is met.

* Extinct: World that once had life, but is now extinct.
* Organic: A world that contains suitable conditions for life, but living things are either absent or unconfirmed.
* Primordial: A world with only microbial life.
* Subhabitable: A world that has life at a significant diversity but has yet to have a diversity explosion akin to the Cambrian Explosion.
* Habitable: A world in which life has had a significant diversity explosion, similar to Earth
* Superhabitable: A world on which life has had more than one significant diversity explosion without a significant decrease in diversity in between.

## **Temperature Classification**

Astronomical objects are categorized by surface temperature (or, with gaseous worlds, temperature at the 1 Atm level) into eight groups. When a world has vast differences in temperature between the night and day time, the temperature of the night and day are mixed together, like frigid-torrid.

* Scorched: >1200 K
* Torrid: 800-1200 K
* Hot: 400-800 K
* Warm: 300-400 K
* Temperate: 250-300 K
* Cool: 200-250 K
* Cold: 100-200 K
* Frigid: <100 K

## **Ring System Classification**

A ring system is a disc or ring orbiting an astronomical object. Ring systems are mainly composed of dust or small asteroids, typically called moon-lets. Ring systems are commonly found around Jovias, but small ring systems have been found on asteroids and dwarf planets. Ring systems are made from collisions or by smaller planets and moons, hitting it's Roche limit. Ring systems can also be composed of many parts parts.. Ring systems are classified into 3 distinct types, based on the ring system's material.

* Rocky: The second most common type of ring systems, the rocky ring systems are rich in various rocks. These ring systems are typically present on worlds near their host star.
* Metallic: Metallic ring systems are rare ring systems which are rich in various metals. Most commonly, hot jovians possess metallic ring systems
* icy: The most common of rings, icy ring systems possess a high amount of ice, most commonly water-ice. They are the most common type of ring systems, found around many neptunians and colder worlds.

## **Asteroid Classification**

Asteroids are simply defined as airless rocks and boulders floating through outer space. They are mainly just minor planets that were unable to obtain enough mass to enter a spherical shape, but are too small to be recognized as dwarf planets. There can be millions of asteroids in one star system, each one with different compositions. Asteroids have five distinct classes based on their composition.

* Class C: The most common type of asteroid, includes a lot of carbon in their composition
* Class S: The second most common type of asteroid, mainly made of silicates
* Class M: Very rare, made of a lot of metals
* Class I: Rather common, made mainly of ice
* Class E: The rarest, the E class asteroids have a large amount of rare elements in its composition