Planet classifications exist to provide a systematic and organized way of categorizing and understanding the diverse range of celestial bodies found throughout the universe. These classifications serve several important purposes. Firstly, they allow scientists and researchers to study and compare planets based on their shared characteristics, such as size, composition, and environmental conditions. This aids in the identification of patterns, trends, and relationships between different types of planets. Secondly, classifications help in the exploration and colonization of space by providing valuable information about the suitability of planets for human habitation and resource extraction. They guide astronomers, explorers, and future settlers in identifying planets that may have the necessary conditions to support life or provide valuable resources. Additionally, planet classifications aid in communication and the dissemination of knowledge about planets. They provide a common language for scientists, enabling them to share information, conduct research, and collaborate on a global scale. Overall, planet classifications play a crucial role in expanding our understanding of the cosmos and shaping our exploration and utilization of space resources.
A / Geothermal
| Type: | Rock |
| Age: | 0-2 Billion Years |
| Atmosphere: | Sulfer Dioxide / Carbon Dioxide |
| Radius: | 500 to 5,000 km |
| Surface: | Rocky / Partially Molten |
| Composition: | Igneous Silica and Basalt |
| Location: | Any |
| Habitability: | None |
Class A planets are small, barren worlds teeming with volcanic activity. The volcanic activity traps carbon dioxide in the atmosphere, resulting in high temperatures regardless of the planet's location within a star system. Once the volcanic activity ceases, the planet is considered "dead" and reclassified as a Class C planet. An example of a Class A planet is Gothos.
B / Geomorteus
| Type: | Rock |
| Age: | 0-10 Billion Years |
| Atmosphere: | Helium / Sodium / Oxygen |
| Radius: | 500 to 5,000 km |
| Surface: | Barren / Molten in Places |
| Composition: | Iron, Potassium, Silicon |
| Location: | Hot Zone |
| Habitability: | None |
Class B planets are typically small worlds located within a star system's Hot Zone. These planets are not suitable for humanoid life due to their thin atmospheres primarily composed of helium and sodium. The surface is molten and highly unstable, with temperatures ranging from 450° in the daylight to nearly -200° at night. Despite their small size, Class B planets are often extremely dense, with a large inner core that can make up to 55% of the planet's volume. Examples include Mercury and Nebhillium.
C / Geoinactive
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | None |
| Radius: | 500 to 10,000 km |
| Surface: | Barren and Cratered |
| Composition: | Anthracite and Basalt / Layers of Frozen Hydrocarbons & Water |
| Location: | Hot Zone / Echosphere / Cold Zone |
| Habitability: | None |
Class C planets, often referred to as "dead worlds," are characterized by their lack of geological activity and absence of an atmosphere. These rocky and barren worlds can exist in any zone of a star system, with surface temperatures largely dependent on their proximity to the central star. Typically, temperatures range from -150 to -120 degrees Celsius, although exceptions exist. Despite their seemingly inhospitable conditions, Class C planets are often rich in minerals, making them prime candidates for future mining operations.
The evolution of planets from one class to another is a fascinating aspect of planetary science. Class A and B planets, as they cool down over billions of years, often transition into Class C planets. Similarly, Class E planets can evolve into Class C if they are too close to their parent star and lose their atmosphere due to the star's heat or gravitational pull.
D / Dwarf / Plutonian
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | None / Very Tenuous |
| Radius: | 50 to 3,000 km |
| Surface: | Barren / Cratered |
| Composition: | Frozen Hydrocarbons and Ice |
| Location: | Any |
| Habitability: | None |
Class D planets, also known as Plutonian objects, are small worlds primarily composed of ice. They are generally not considered true planets. Many moons and asteroids fall into this category, as do larger objects in a star system's Kuiper Belt. Examples include Pluto, Ceres, and Eredas-II.
E / Geoplastic
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | Hydrogen Compounds |
| Radius: | 5,000 to 10,000 km |
| Surface: | Molten with High Surface Temperature |
| Composition: | Silicone, Iron, Magnesium, Aluminum |
| Location: | Any |
| Habitability: | Carbon Cycle Life |
Class E planets, often considered the infancy stage of a habitable planet, are characterized by their molten core and crust. Their location, often too close to their parent star and within the Hot Zone, subjects them to solar winds and radiation, resulting in extremely high surface temperatures. The atmosphere of these planets is typically thin, composed mainly of hydrogen and helium.
The evolution of a Class E planet is largely dependent on its proximity to its parent star. If a Class E planet forms too close to its star, it will slowly transition through the stages of Class F, G, and P worlds as it cools. After billions of years, when geological activity ceases, it will become a Class C world. If a Class E planet is within the star's habitable zone, also known as the Ecosphere, it can develop along a trajectory toward a Class M world after transitioning through Class G. This is the most common projection for a Class E world, as they exist more commonly within the Ecosphere.
Conversely, a Class E planet that develops just outside of a star's habitable zone in the cold zone follows a different trajectory. As it cools, it transitions into a cold Class F world, then Class G, eventually becoming a Class P world. If such a world is too far outside of the star's ecosphere, it dies as geological heat dissipates. Instead of developing into a Class G world, it evolves into a frozen glaciated Class P world with minimal simple life forms. Eventually, it loses its atmosphere due to the condensation and freezing of hydrocarbons, or lighter elemental gases such as hydrogen and helium bleed away into space, resulting in a transition to a Class C world.
F / Geometallic
| Type: | Rock |
| Age: | 1-3 Billion Years |
| Atmosphere: | Carbon Dioxide, Ammonia, Methane |
| Radius: | 5,000 to 10,000 km |
| Surface: | Volcanic and Barren |
| Composition: | Silicone, Iron, Magnesium, Aluminum |
| Location: | Any |
| Habitability: | Bacteria |
Class F planets are a transition stage from Class E, where the crust and core have started to solidify. These planets are characterized by their high volcanic activity, which contributes to the formation of shallow seas as the steam from volcanic eruptions condenses into water. Simple bacterial life begins to thrive in these conditions.
In the Ecosphere, the most common location for these planets, they begin to develop bacterial life. As the core cools sufficiently, the volcanic activity ceases, marking the transition of the planet to Class G. An example of a Class F planet is Janus IV.
When a Class F planet forms within the hot zone of a star, the intense heat and radiation typically prevent the development of bacterial life. Despite retaining an atmosphere, the surface becomes extremely hot. Instead of transitioning to a Class G world, it remains a Class F until it cools down to become a Class C world. This process takes billions of years. The extreme conditions of the hot zone result in a unique evolutionary path for Class F planets, distinguishing them from those that form within a star's habitable zone or ecosphere.
When a Class F planet forms just inside the cold zone of a star, it develops a protective layer of ice due to the condensation of water. Despite the cold exterior, the planet's interior remains warm enough for simple bacterial life to develop. This slow transformation of the atmosphere leads the planet to evolve into a glaciated Class P world with minimal simple life forms, rather than a Class G world.
G / Geocrystalline
| Type: | Rock |
| Age: | 3-4 Billion Years |
| Atmosphere: | Carbon Dioxide, Oxygen, Nitrogen |
| Radius: | 5,000 to 10,000 km |
| Surface: | Rocky and Mostly Barren |
| Composition: | Silicone, Iron, Magnesium, Aluminum |
| Location: | Any |
| Habitability: | Vegetation / Simple Organisms |
Class G planets represent a significant step in the evolution of a habitable planet. Once the core of a Class F planet has cooled sufficiently, and volcanic activity has lessened, the planet transitions into a Class G. At this stage, the atmosphere contains oxygen and nitrogen in some abundance, which fosters the growth of increasingly complex organisms. Primitive vegetation, such as algae, begins to appear, along with simple animal life forms akin to sponges and jellyfish. As the surface continues to cool, a Class G planet can evolve into a Class H, K, L, M, N, O, or P world. Delta Vega is a notable example of a Class G planet.
When a Class G planet forms within the cold zone of a star, it develops a protective layer of ice due to the condensation of water. The planet's interior remains warm, allowing for the growth of bacteria and potentially some simple plant life under the ice. However, the transformation of the atmosphere occurs at a slower pace compared to a planet within the ecosphere. As the planet cools, it transitions into a frozen, glaciated Class P world with minimal simple life forms.
In contrast, a Class G planet forming within the hot zone of a star faces a different fate. The intense heat and radiation create a barrier that prevents the planet from retaining an atmosphere as it cools. Life on such a planet would be exceedingly rare, if not impossible. As the planet cools it remains a Class G until it cools down enough and geological activity ceases to become a Class C world, a process that takes billions of years.
H / Desert
| Type: | Rock |
| Age: | 4-10 Billion Years |
| Atmosphere: | Oxygen, Nitrogen, Argon, and Metals |
| Radius: | 5,000 to 10,000 km |
| Surface: | Hot / Arid with < 20% Surface Water |
| Composition: | Silicone, Iron, Magnesium, Aluminum |
| Location: | Ecosphere |
| Habitability: | Drought-Resistant Plants & Animals |
Class H planets, also known as desert worlds, are characterized by their minimal water coverage, with less than 20% of their surface being water. The primary characteristic of a Class H world is its aridity, with little precipitation received. While many Class H worlds are covered in sand, it is not a requirement for this classification.
The life forms on these planets have adapted to the harsh conditions, with drought-resistant plants and animals being common. In fact, many Class H worlds are inhabited by humanoid populations. While most Class H worlds are hot and arid, conditions can vary greatly. Examples of Class H planets include Nimbus III and Ocampa.
I / Ice Giant / Uranian
| Type: | Gas Giant |
| Age: | 2-10 Billion Years |
| Atmosphere: | Hydrogen and Helium |
| Radius: | 15,000 to 50,000 km |
| Surface: | Rock, Ice, Methane, and Ammonia |
| Composition: | Hydrogen, Helium |
| Location: | Cold Zone |
| Habitability: | None |
Ice Giants, also known as Uranian planets, are the most common class of gaseous giants with a composition distinct from other giant worlds. The core of these planets is primarily composed of rock and ice, surrounded by a thin layer of liquid methane, water, and ammonia. One of the defining characteristics of Ice Giants is their sharply inclined magnetic field, which is not aligned with the axis of rotation. These planets typically form on the fringes of a star system, far from the central star. Their formation and evolution processes are influenced by the colder temperatures and different material availability in these outer regions.
J / Jovian
| Type: | Gas Giant |
| Age: | 2-10 Billion Years |
| Atmosphere: | Hydrogen , Helium |
| Radius: | 25,000 to 250,000 km |
| Surface: | Liquid Metallic Hydrogen |
| Composition: | Gaseous and Liquid Hydrogen & Helium / Liquid Metallic Hydrogen |
| Location: | Cold Zone |
| Habitability: | None |
Class J planets, also known as gas giants, are massive spheres primarily composed of liquid and gaseous hydrogen, with small cores of metallic hydrogen. They are characterized by their extremely turbulent atmospheres, where wind speeds can reach up to 600 kph in the most severe storms. Many Class J planets also boast impressive ring systems, primarily composed of rock, dust, and ice. These planets typically form in the Cold Zone of a star system, albeit much closer than Class I planets. Their strong magnetic and gravitational fields can pose a navigational hazard to nearby vessels. Moreover, these fields can make the extraction of Hydrogen more challenging than on Class I worlds.
Despite the harsh conditions, the sheer size and unique composition of Class J planets make them a subject of great interest for scientific exploration and study. Examples of Class J planets include Jupiter and Saturn in our own solar system.
K / Adaptable
| Type: | Rock |
| Age: | 4-10 Billion Years |
| Atmosphere: | Oxygen, Nitrogen, Argon |
| Radius: | 2,500 to 7,500 km |
| Surface: | Barren and Cratered |
| Composition: | Silicone, Iron, Magnesium, Aluminum |
| Location: | Ecosphere |
| Habitability: | Adaptable |
Class K planets, also known as adaptable planets, are characterized by their barren surface with little or no surface water and a thin atmosphere primarily composed of carbon dioxide. These planets, which are typically found within the ecosphere of a star system, have an age that ranges from four to ten billion years. Lifeforms on Class K planets are limited to single-celled organisms. However, these planets can be adapted for humanoid life through the use of pressure domes. Despite the harsh conditions, Class K planets like Mars have been colonized by humanoids using pressure domes, and are often prime candidates for terraforming.
L / Marginal
| Type: | Rock |
| Age: | 4-10 Billion Years |
| Atmosphere: | Argon & Oxygen with Trace Elements |
| Radius: | 5,000 to 7,500 km |
| Surface: | Rocky with Little Surface Water |
| Composition: | Silicone, Iron, Magnesium, Aluminum |
| Location: | Ecosphere |
| Habitability: | Vegetation Only |
Class L planets, also known as marginal planets, are barely habitable worlds that can have varying types of atmospheres. Some of these atmospheres are suitable for humanoid life, while others are not without additional means. These planets typically have higher concentrations of carbon dioxide than Class M worlds. Vegetation is common on Class L worlds, but they are usually devoid of fauna. Despite the harsh conditions, Class L planets are considered to have a breathable atmosphere but are environmentally hostile. These planets are prime candidates for colonization and potential terraforming. They have ages that range from four to ten billion years. Marginal planets are located within the ecosphere of a star system. They are characterized by a rocky and barren surface with little surface water. Native lifeforms are limited to plant life, although the majority of Class L planets are suitable for humanoid colonization. Examples of Class L planets include Indri VIII and the crash site planet of the USS Olympia.
M / Minshara / Terrestrial
| Type: | Rock |
| Age: | 4-10 Billion Years |
| Atmosphere: | Oxygen, Nitrogen, Argon |
| Radius: | 5,000 to 10,000 km |
| Surface: | Abundant Surface Water, Temperate Climate |
| Composition: | Silicone, Iron, Magnesium, Aluminium |
| Location: | Ecosphere |
| Habitability: | Prime conditions for large populations of animal, planet, and humanoid life. |
Class M planets, also known as terrestrial or Earth-like planets, are the most hospitable to carbon-based life forms and are therefore the most interesting to astrobiologists. These planets are characterized by their silicate-rock composition and are typically located within a star system's habitable zone, allowing for the presence of liquid water on their surfaces.
The climate of Class M planets is generally temperate, with surface temperatures that can support the existence of liquid water. The surface of these planets is usually between 20% and 80% water, allowing for the existence of vast oceans and wide swaths of verdant forest. However, conditions can vary greatly between Class M worlds. Some may be dry and rocky, while others may be cold and snowy, but as long as the climate is generally temperate and the atmosphere is composed of oxygen and nitrogen, they can be classified as Class M. Despite the variations in conditions, Class M planets are well-suited for humanoid colonization and are often prime candidates for terraforming. They are the most similar to Earth in terms of environmental conditions and the potential for supporting life.
N / Reducing
| Type: | Rock |
| Age: | 3-10 Billion Years |
| Atmosphere: | Carbon Dioxide and Sulfides |
| Radius: | 5,000 to 10,000 km |
| Surface: | Barren with High Surface Temperatures |
| Composition: | Silicone, Iron, Magnesium, Aluminium |
| Location: | Ecosphere |
| Habitability: | None |
Class N planets, also known as reducing planets, are terrestrial planets characterized by high surface temperatures and a dense, acidic atmosphere due to a greenhouse effect. Water exists only in the form of vapor on these planets. The high surface temperature is fueled by the greenhouse effect, and the extremely dense atmosphere is comprised of carbon dioxide and sulfides. These planets, which range in age from 3 to 10 billion, are typically located in the ecosphere of their parent stars. Venus is a textbook example of a Class N planet.
A reducing atmosphere, as found on Class N planets, is an atmospheric condition in which oxidation is prevented by the removal of oxygen and other oxidizing gases or vapors, and which may contain actively reducing gases such as hydrogen, carbon monoxide, and gases such as hydrogen sulfide that would be oxidized by any present oxygen. This type of atmosphere is considered to be more conducive to life, as it can lead to the formation of organic compounds necessary for the origin of life.
Despite these conditions, life as we know it is not possible on Class N planets due to the extreme surface temperatures and atmospheric pressure, which is more than 90 times that of a Class M world. The dense, carbon dioxide-rich atmosphere and the presence of sulfides make these planets inhospitable to most forms of life. These worlds can be terraformed and with the use of artificial environments like pressure domes, they can be colonized.
O / Oceanic / Pelagic
| Type: | Rock |
| Age: | 3-10 Billion Years |
| Atmosphere: | Oxygen, Nitrogen, Argon |
| Radius: | 5,000 to 10,000 km |
| Surface: | 80% Water & Archipelagos |
| Composition: | Silicone, Iron, Magnesium, Aluminium |
| Location: | Ecosphere |
| Habitability: | Vegetation, Cetacean, Animal, Humanoid |
Class O planets, often referred to as Pelagic or Oceanic planets, are characterized by their vast, global oceans. Over 90% of their surface is covered in water, making them similar to Class M planets but with a significantly higher water-to-land ratio. These planets are located within a star system's habitable zone, or ecosphere, which allows for the existence of liquid water on their surface. The vast oceans of Class O planets give rise to a unique ecosystem, teeming with aquatic life forms. The minimal landmasses that do exist are often small islands or archipelagos. Despite the predominance of water, these planets can support a breathable atmosphere for many life forms, including humanoids. The scarcity of land can pose challenges for colonization and resource extraction. Despite these challenges, Class O planets are often of scientific interest due to their unique ecosystems and potential for discovering new aquatic species. Examples of Class O planets include Alarin III, Ciden II, and Indri VII.
P / Glaciated
| Type: | Rock |
| Age: | 3-10 Billion Years |
| Atmosphere: | Oxygen, Nitrogen, Argon |
| Radius: | 5,000 to 10,000 km |
| Surface: | Cold, Glaciated |
| Composition: | Silicon, Iron, Magnesium, Ice |
| Location: | Ecosphere and Cold Zone |
| Habitability: | Varied; Cold-Resistant Vegetation, Animal, and Humanoid / Bioluminescent Single-Celled Organisms / Possibly None |
Class P planets, also known as Glaciated worlds, exist on the distant edge of a star system's ecosphere. These habitable planets, while still numerous, are starkly different from the lush garden worlds found closer to the center. Class P worlds are characterized by their cold, barren, and glaciated surfaces, covered in solid ice. While some may possess narrow stripes of green along the equator, where hearty plant and animal life can flourish, many glaciated worlds remain entirely frozen. Despite the harsh conditions, humanoid life can thrive on these frigid planets.
When a Class P planet forms within the ecosphere of a star, it tends to develop some form of cold-resistant life forms. During this phase, the planet is still kept warm by geological activity rather than direct sunlight. Bioluminescent bacteria and other single-celled organisms can survive deep within the planet, where geological heat maintains a layer of liquid water. However, as the planet continues to cool, this layer of liquid water eventually freezes, and the world effectively enters a dormant state. These worlds typically retain their atmosphere, with heavier diatomic elements like oxygen and nitrogen. Over time, thick layers of permafrost build up, covering the frozen surface.
Despite the challenging conditions, Class P worlds have the potential for terraforming. If the ice were to thaw, dormant single-celled bacteria and similar life forms may revive and propagate. However, the freezing of the planet into a Class C world is the most likely outcome after several billion years. The geological heat diminishes, the atmosphere becomes thinner, and the surface freezes completely. These worlds represent a fascinating evolutionary journey, from the formation of cold-resistant life forms to the eventual freezing and transformation into Class C worlds.
Examples of Class P worlds include Andorra and Rita Penthe, which showcase the diversity and unique characteristics of these frigid and glaciated planets.
Q / Variable
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | Varies - Nitrogen, Oxygen, Argon Ranging from Thin to Very Dense |
| Radius: | 2,000 to 7,500 km |
| Surface: | Varies - Molten, Frozen, Jungle, etc. |
| Composition: | Silicon, Iron, Magnesium |
| Location: | Any |
| Habitability: | None |
Class Q worlds, rare and enigmatic, are planetoids that typically form in highly eccentric orbits or near stars with variable outputs. The conditions on the surface of these planets are characterized by extreme variations. Deserts and rainforests can exist within just a few kilometers of each other, while glaciers may be found in close proximity to the equator. The constant instability and unpredictability of the environment make it virtually impossible for life to thrive on Class Q worlds.
The wide range of temperatures and ecological disparities make these planets inhospitable to complex organisms. The erratic climate and geological conditions create an ever-changing landscape, where extreme temperature fluctuations and geological upheavals are the norm. The lack of a stable and consistent environment prevents the development and sustenance of ecosystems and organisms.
Examples of Class Q worlds include the Genesis Planet, which showcases the dramatic and volatile nature of these planetoids. The Genesis Planet exhibits the striking coexistence of contrasting environments, from lush forests to barren deserts, in close proximity to each other.
R / Rogue
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | Volcanic Outgassing |
| Radius: | 7,500 to 10,000 km |
| Surface: | Hot, Temperate, or Cold |
| Composition: | Silicate Compounds and Iron |
| Location: | Interstellar Space |
| Habitability: | Non-Photosynthetic Plants and Animals if Any |
Class R planets, intriguing and rare, have a distinct origin and evolution. These planets typically form within a star system but undergo a significant shift in their trajectory at some point in their evolution. The expulsion of a Class R planet can occur due to catastrophic events such as a massive asteroid impact or the destruction of another planet within the system. Additionally, the gravitational influence of high-mass objects like black holes passing close to the planet can lead to its ejection from its original orbit.
The expulsion of a planet from its star system radically alters its evolutionary path. While many ejected planets become lifeless and inhospitable, geologically active Class R planets can sustain a habitable surface through volcanic outgassing and geothermal venting. These processes contribute to the heating of the planet's atmosphere, allowing for the possibility of minimal environments conducive to the evolution of non-photosynthetic organisms. These unique conditions often involve perpetual darkness and rely on geothermal energy for sustenance.
Class R planets are exceptionally rare, and the ability of an ejected planet to support or evolve life is even rarer. In most cases, an expelled planet transitions to the classifications of Class C3, Class D3, or becomes a rogue planet (Class C or D) based on specific subclassifications. To be classified as a Class R planet, it must possess an atmosphere heated by geothermal energy and no longer orbit a star.
The study of Class R planets provides valuable insights into the diversity of planetary systems and the potential for life to persist or adapt in extreme and unconventional environments. While the circumstances for the development and sustenance of life on Class R planets are challenging, they serve as a reminder of the resilience and adaptability of life in the universe.
S / Gas Supergiant
| Type: | Gas Giant |
| Age: | 2-10 Billion Years |
| Atmosphere: | Hydrogen and Helium |
| Radius: | 250,000 to 50,000,000 km |
| Surface: | Liquid Metallic Hydrogen |
| Composition: | Gaseous and Liquid Hydrogen & Helium / Liquid Metallic Hydrogen |
| Location: | Cold Zone |
| Habitability: | None |
Class S planets, known as Super Giants, are characterized by their immense size and share many similarities with Class J planets, also known as Jovian planets. These colossal worlds feature a core composed of liquid metallic hydrogen, surrounded by an atmosphere predominantly made up of hydrogen and helium. Class S planets are typically found in the cold zone of a star system and often exhibit spectacular ring systems, as well as host numerous moons.
One of the significant roles of giant worlds like Class S planets is their function as "shields" for the inner terrestrial planets within a star system's ecosphere. Due to their massive gravitational fields, these planets have the capacity to divert comets and asteroids away from the interior of the star system, providing a protective barrier for the habitable worlds. This gravitational influence helps to reduce the frequency and impact of potentially catastrophic celestial objects on the inner planets.
Class S planets, with their striking presence and gravitational influence, contribute to the dynamic and complex dynamics of star systems. Their ability to attract and interact with celestial bodies adds a layer of complexity to the overall structure and stability of the system. The study of Class S planets provides insights into the formation and evolution of star systems, as well as the factors that contribute to the habitability and protection of inner planets.
T / Transitional
| Type: | Gas Giant / Rock Hybrid |
| Age: | 2-10 Billion Years |
| Atmosphere: | Frozen Hydrocarbons, Ice, Hydrogen, Helium |
| Radius: | 250,000 to 25,000,000 km |
| Surface: | Liquid Metallic Hydrogen |
| Composition: | Osmium, Iridium, Platinum, Tungsten |
| Location: | Cold Zone |
| Habitability: | None |
Class T planets, often referred to as gas dwarfs, occupy a size range between the ice giants of Class I and the super-terrestrial worlds of Class V. These planets are characterized by their significant size and strong gravitational pull, allowing them to retain a thick atmosphere composed of hydrogen, helium, and hydrocarbons.
The atmospheric composition of Class T planets transitions into oceans consisting of semiliquid compressed hydrogen combined with semisolid ice or hydrocarbon compounds. Beneath these vast hydrogen and ice layers lies a core made up of metallic ores. Despite being called gas dwarfs, the term is somewhat misleading considering their substantial size and the complex composition of their interiors.
Class T planets showcase the diversity of planetary formations and highlight the various states of matter that can exist within their atmospheres and interiors. The combination of hydrogen, helium, and hydrocarbons in the atmosphere, along with the presence of semiliquid hydrogen and ice oceans, creates a unique environment different from other classes of planets.
U / Gas Ultragiant
| Type: | Gas Giant |
| Age: | 2-10 Billion Years |
| Atmosphere: | Hydrogen and Helium |
| Radius: | 25,000,000 to 60,000,000 km |
| Surface: | Liquid Metallic Hydrogen |
| Composition: | Gaseous and Liquid Hydrogen & Helium / Liquid Metallic Hydrogen |
| Location: | Cold Zone |
| Habitability: | None |
Class U planets, also known as ultragiants, represent the pinnacle of planetary mass. These colossal worlds are predominantly found in the Cold Zone of a star system and share structural similarities with Class S and J planets, albeit on a much grander scale. Most Class U planets remain content to reside in the outer regions of a star system, exerting their gravitational influence on the surrounding celestial bodies. However, if a Class U planet reaches a sufficient mass, approximately 13 times that of Jupiter, a remarkable transformation occurs. The deuterium within the planet's core ignites nuclear fusion, leading to the birth of a red dwarf star. This extraordinary event creates a binary star system, with the ultragiant planet now shining as a companion to its stellar sibling.
The immense mass of ultragiants can occasionally disrupt their orbital dynamics, causing them to spiral inward towards the central region of the star system. In this scenario, the ultragiant becomes a "Hot Jupiter," a gas giant that orbits in close proximity to its parent star. This disruptive process can lead to the ejection of smaller planets from the system into interstellar space, ultimately resulting in the transformation of the Class U planet into a desolate and barren Class X world.
Class U planets exemplify the extremes of planetary existence, pushing the boundaries of what is possible in terms of size, mass, and cosmic interactions. Their presence within a star system can have far-reaching effects, shaping the dynamics of planetary systems and offering a glimpse into the immense diversity of celestial bodies in the universe.
V / Super-Terrestrial
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | Carbon Dioxide, Oxygen, Hydrogen, Helium |
| Radius: | 10,000 to 15,000 km |
| Surface: | High Pressure / Temperature |
| Composition: | Iron, Iridium, Tungsten, Nickel |
| Location: | Ecosphere / Cold Zone |
| Habitability: | Pressure Resistant Planet / Animal Life |
Class V planets, often referred to as "super-Earths," occupy an intermediate size range between terrestrial planets and ice giants. These large rocky or metallic worlds possess higher gravity, enabling them to retain dense atmospheres rich in hydrogen. Surface conditions on Class V planets are characterized by high temperatures and pressures, making them inhospitable for humanoid habitation. However, the extreme environment can give rise to complex life forms that are resistant to the harsh conditions, making these planets potentially viable for colonization using specialized structures such as pressure domes.
One notable characteristic of Class V planets is their elevated surface temperature, a consequence of the higher gravity, pressure, and temperature that prevail on these worlds. The combination of these factors creates an environment where only life forms capable of withstanding extreme conditions can survive and evolve. Even when Class V planets form in the Cold Zone of a star system, their higher gravity may allow them to maintain suitable environments for life, albeit with unique adaptations to cope with the challenging circumstances. The gravitational pull experienced on these planets can be significantly stronger than that on Earth, presenting additional challenges for potential colonization efforts.
In rare instances, the surface environment on Class V planets may reach such extreme conditions that certain compounds undergo phase transitions and revert to a plasma state due to the intense heat and pressure. This further underscores the hostile nature of these worlds and the need for specialized adaptations and technologies to enable survival and exploration.
W / Divided / Locked
| Type: | Rock |
| Age: | 0-10 Billion Years |
| Atmosphere: | Oxygen / Sodium / Hydrogen |
| Radius: | 500 to 10,000 km |
| Surface: | Half Barren / Molten and Half Cold, Glaciated |
| Composition: | Iron, Potassium, Silicon |
| Location: | Hot Zone / Ecosphere |
| Habitability: | None |
Class W worlds, also known as tidally locked planets, are rocky planets that experience a gravitational interaction with other bodies in their star system, causing them to become permanently locked in a synchronous rotation. As a result, one side of the planet is constantly facing the parent star or sister planet, while the other side remains in perpetual darkness.
The illuminated side of a Class W planet is subjected to intense heat and overexposure to stellar radiation, giving rise to molten areas and a burnt, desert-like surface. The extreme conditions make this region inhospitable for most forms of life as the surface temperatures can be exceedingly high. In contrast, the far side of the planet remains shrouded in perpetual darkness and experiences extreme cold. However, if the planet possesses a dense atmosphere, there may be a temperate zone separating the illuminated and dark sides, where conditions are more moderate.
Despite the challenging environment, Class W planets have the potential for colonization and may even harbor native life that has adapted to the extreme conditions in unique ways. The presence of a dense atmosphere can play a crucial role in mediating the heat distribution and creating habitable regions along the temperate dividing line. In these areas, life forms may have evolved specialized adaptations to survive in the stark contrast between light and dark, utilizing alternative energy sources or developing robust protective mechanisms.
Class W worlds offer intriguing opportunities for scientific exploration and the study of extremophile life forms. The colonization of these planets would require careful consideration and the development of advanced technologies to mitigate the harsh environmental conditions. Nonetheless, the presence of native life that has adapted to the extreme environment highlights the resilience and adaptability of organisms in the face of challenging circumstances.
X / Chthonian
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | None |
| Radius: | 500 to 5,000 km |
| Surface: | Barren & Extremely Hot |
| Composition: | Molten Iron |
| Location: | Hot Zone |
| Habitability: | None |
Class X worlds, also known as stripped planets, are a unique category of celestial bodies that arise from the failed development of Class S or U planets in the Hot Zone of a star system. These planets experience a catastrophic event that leads to the stripping away of their hydrogen/helium atmosphere, leaving behind only a dense, metal-rich core.
Unlike their gas giant counterparts, Class X planets lack an atmosphere and possess a small, barren surface akin to a Class B planet. The absence of an atmosphere renders these worlds inhospitable for life as they lack the protective shield and atmospheric conditions necessary for sustaining complex organisms. The dense, metal-rich core distinguishes them from other planet types, and their barren nature makes them uninhabitable for humanoid colonization.
Class X planets are rare and hold significant scientific and economic value. Despite their desolate nature, their metal-rich composition can make them targets for resource extraction and mining operations. However, their fate is ultimately sealed, as their proximity to the parent star renders them susceptible to absorption over time. The gravitational pull from the star eventually engulfs the Class X planet, leading to its demise.
Y / Demon
| Type: | Rock |
| Age: | 2-10 Billion Years |
| Atmosphere: | Turbulent with Toxic Radiation |
| Radius: | 5,000 to 7,500 km |
| Surface: | Barren & Extremely Hot |
| Composition: | Molten Iron & Sulphur, Deuterium, Silicates |
| Location: | Hot Zone |
| Habitability: | None |
Class Z planets, also known as Demon Class planets, represent some of the most inhospitable and environmentally unfriendly celestial bodies in the galaxy. These planets, often found in the hot zone of star systems, possess highly toxic atmospheres, violent storms, and extreme surface conditions that make them uninhabitable for life as we know it.
The defining characteristic of Class Z planets is their thick, toxic atmosphere, which is filled with harmful gases and subjected to violent thermionic radiation discharges. The atmospheric composition and extreme conditions create an environment that is lethal to most known forms of life. Surface temperatures on these planets can exceed 200°C, and winds can reach staggering speeds of 500 kph, further contributing to the hostile conditions.
While Class Z planets are generally unremarkable in terms of their physical characteristics and average size, their harsh atmospheres make them stand out as exceptionally hostile environments. The surface of these planets is typically barren, composed primarily of iron, deuterium, and silicate rocks.
It is worth noting that life on Class Z planets is exceedingly rare. In fact, the discovery of a type of biomimetic life form on a Class Z planet in the Delta Quadrant in 2374 stands as the only recorded instance of life found in such an extreme environment.
Specialized Sub-Classes
These sub-classes are applicable to certain types of planets in special conditions.
1 / Retinal
Applicable to Class H, L, M, O, and P.
On most planets, indigenous vegetation utilizes chlorophyll-based photosynthesis, resulting in a familiar world with blue oceans and green forests. However, terrestrial planets in orbit of red dwarf stars receive insufficient light for chlorophyll-based photosynthesis. Instead, vegetation on these planets relies on retinal-based photosynthesis, resulting in a world covered in purple vegetation.
For example, a Class M planet in orbit of a red dwarf star is operationally identical to a Class M planet in orbit of any other star. Hence, a terrestrial planet in a red dwarf star system retains its primary classification as Class M, but with the addition of the retinal subclass as a secondary classification. A Class M planet in this context is identified as Class M1 or sometimes Class M (Retinal).
2 / Satellite
Applicable to nearly any rocky world, Class A, B, C, D, E, F, G, H, K, L, M, N, O, P, Q, and Y.
When a celestial body orbits another planet, it is labeled as a satellite, commonly referred to as a moon. Moons come in various shapes and sizes. While many are small, barren chunks of rock, some moons can be habitable Class M worlds that would be considered planets if they were in orbit around a star. Class Q2 satellites are more common than full Class Q worlds due to the irregular exposure to the central star of a system resulting from the moon's orbital path around a gaseous planet.
Regardless of their shape and size, all moons are assigned the satellite subclass. For example, a Dwarf-class planet (Class D) in orbit of another planet would be designated as Class D2, Class D Satellite, or Class D Moon. Normally, if a moon is a typical non-life-bearing moon with unremarkable features (such as Earth's Moon in the Sol system), its official class is not needed. The same applies to asteroidal moons that exhibit typical characteristics (such as the two moons of Mars in the Sol system).
3 / Ejected / Rogue
Applicable to worlds unable to maintain their surface temperature to become a Class R or are gas giants, Class C, D, I, J, S, T, U, and V.
When a planet is ejected from its orbit around a star, such as in the case of a Class R, but cannot sustain its surface temperature, it falls under subtype 3. These planets rapidly cool when no longer exposed to the heat of a star. Rock worlds typically become Class C or D, while gas giants retain their original class but are designated as Rogue, denoting their existence in interstellar space. In rare cases, a Class U planet slowly accumulates enough mass to ignite fusion, becoming a dwarf star in its own right. Rock planets lacking geothermal heat and an atmosphere are classified as Ejected/Rogue. Refer to Class R for further details.
Class T or V worlds that are ejected from their natural orbits can maintain surface temperatures not through geothermal emissions but rather due to the intense pressure provided by their size and incredibly strong gravitational fields. Such worlds are exceedingly rare, even more so than Class R worlds with intelligent life, as Class T or V worlds are scarce to begin with.
These planets are classified as Class I3, Ejected Class I, or Rogue Class I.
4 / Large / Heavy
Applicable to nearly any rocky world, Class A, B, C, D, E, F, G, H, K, L, M, N, O, P, Q, and Y.
Some planets do not fit precisely into an existing classification. The Large subclass specifically identifies a planet that otherwise fits an existing classification but is unusually large or heavy. These planets possess all the characteristics of their respective classes, except for their size/mass. Such worlds are not rare, but this subclass is primarily used for precise cataloging purposes. It may be used explicitly to differentiate them from other classifications, especially when other planets in the system share the same class but fall within size/mass guidelines. These worlds often have thicker atmospheres and higher gravity compared to their more common counterparts. While these planets tend to deviate from the ideal conditions of Class M or O, they are often classified as Class N, H, K, L, or P.
Examples include Class E4, Heavy Class E, or Large Class E.
5 / Small / Light
Applicable to nearly any rocky world, Class A, B, C, D, E, F, G, H, K, L, M, N, O, P, Q, and Y.
Some planets do not fit precisely into an existing classification. The Small subclass specifically identifies a planet that otherwise fits an existing classification but is unusually small or light. These planets possess all the characteristics of their respective classes, except for their size/mass. Such worlds are not rare, but this subclass is primarily used for precise cataloging purposes. It may be used explicitly to differentiate them from other classifications, especially when other planets in the system share the same class but fall within size/mass guidelines. These worlds often have thinner atmospheres and lower gravity compared to their more common counterparts. Unlike subclass 4 worlds, many of these planets do not reach Class M or O status and tend more towards Class H, K, L, N, or P. This is primarily due to their smaller gravitational pull, which is insufficient to retain the thicker atmospheres required for Class M/O classification. These planets are rarer than their larger counterparts, unless they possess an unusually dense core capable of retaining more atmosphere and water.
Examples include Class L5, Light Class L, or Small Class L. While the term "Dwarf" is occasionally used colloquially, it is not considered an official designation to avoid confusion with Class D.
6 / Artificial Ocean
Applicable only to Class O worlds.
This is a specific type of classification. Class O worlds require over 80% of their surface to be covered in water, even though worlds with 100% water coverage still possess a dense molten rock core that generates the gravitational field necessary to maintain an atmosphere and pressure for liquid water. However, this is not the case for subtype 6 worlds. Also known as Class O6 or Artificial Class O, these worlds are not naturally occurring. They are "Ocean Worlds" held together not by gravity, but by a containment field generated at their core, and they consist entirely of water. As such, the age, size, and evolutionary history of these worlds do not conform to most known standards. The size of an Artificial Ocean world depends entirely on the size of the containment field. Even if life is seeded on these artificial ocean worlds, its evolutionary path would be unique, just like any other planet.
Only one such world has ever been discovered, referred to as The Waters by the Monean in the Delta Quadrant.