Terrestrial planet

A **terrestrial planet**, also called a **telluric planet** or a **rocky planet**, was a planet that was composed primarily of silicate rocks or metals. They are often characterized by having a solid planetary surface, differentiating them with the larger gas giant planets.

## Overview

A planet's relationship to its sun affects its climate and makeup. Terrestrial planets are formed from solid materials because their closeness to their star made conditions more favorable for rock and metal to condense there. Colder conditions farther out from stars mean that lighter, gaseous substances like hydrogen, helium, and water vapor gathered into the huge envelopes of atmosphere which make up gas and ice giants.

Surface conditions on terrestrial planets can vary wildly depending on a variety of factors, from temperate Class-M planets to hellish Class-Y planets. Most sentient species in the Milky Way evolved on terrestrial worlds, and nearly all of the planets considered "habitable" for the majority of species are terrestrial.

## Classes

There are a variety of classifications used by the Federation which categorize various types of terrestrial planets/dwarf planets/planetoids.

* **Class-A:** Geothermal planet
	+ **Age:** 0-2 billion years
	+ **Diameter:** 1,000-10,000 km
	+ **Orbital zone:** Ecosphere/cold zone
	+ **Surface conditions:** Partially molten
	+ **Atmosphere:** Primarily hydrogen compounds
	+ **Progression:** Cools to become C, E, F, G, H, K, L, M, N, O, P, Q, R, or Y-class
	+ **Native lifeforms:** None
	+ **Example:** Gothos
* **Class-B:** Geomorteus planet
	+ **Age:** 0-10 billion years
	+ **Diameter:** 1,000-10,000 km
	+ **Orbital zone:** Hot zone
	+ **Surface conditions:** Partially molten, high surface temperature
	+ **Atmosphere:** Extremely tenuous, few chemically active gases
	+ **Native lifeforms:** None
	+ **Example:** Mercury
* **Class-C:** Geinactive planet
	+ **Age:** 2-10 billion years
	+ **Diameter:** 1,000-10,000 km
	+ **Orbital zone:** Ecosphere/cold zone
	+ **Surface conditions:** Low surface temperature
	+ **Atmosphere:** Frozen
	+ **Native lifeforms:** None
	+ **Example:** LV-426, Psi 2000
* **Class-E:** Geoplastic planet
	+ **Age:** 0-2 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Molten, high surface temperature
	+ **Atmosphere:** Hydrogen compounds and reactive gases
	+ **Progression:** Cools to become F or G-Class
	+ **Native lifeforms:** Carbon-cycle or silicon-based life
	+ **Example:** Excalbia
* **Class-F:** Geometallic planet
	+ **Age:** 1-3 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Volcanic eruptions due to molten core
	+ **Atmosphere:** Hydrogen compounds
	+ **Progression:** Cools to become G-Class
	+ **Native lifeforms:** Silicon-based life
	+ **Example:** Janus VI
* **Class-G:** Geocrystalline planet
	+ **Age:** 3-4 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Crystalizing
	+ **Atmosphere:** Carbon dioxide, some toxic gases
	+ **Progression:** Cools to become H, K, L, M, N, O, or P-Class
	+ **Native lifeforms:** Single-celled life
	+ **Example:** Delta Vega
* **Class-H:** Desert planet
	+ **Age:** 4-10 billion years
	+ **Diameter:** 8,000-15,000 km
	+ **Orbital zone:** Hot zone/ecosphere/cold zone
	+ **Surface conditions:** Hot and arid, little surface water
	+ **Atmosphere:** May contain heavy gases and metal vapors
	+ **Native lifeforms:** Draught and radiation-resistance plant and animal life, silicon or carbon-based
	+ **Example:** LV-223, Klendathu, Carrow, Rigel XII, Tau Cygna V, Tuchanka
* **Class-K:** Adaptable planet
	+ **Age:** 4-10 billion years
	+ **Diameter:** 5,000-10,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Barren, little or no surface water
	+ **Atmosphere:** Thin, mostly carbon dioxide
	+ **Native lifeforms:** Single-celled life, adaptable to colonization through terraforming technologies
	+ **Example:** Mars
* **Class-L:** Marginal planet
	+ **Age:** 4-10 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Rocky and barren, little surface water
	+ **Atmosphere:** Oxygen/argon, high concentration of carbon dioxide
	+ **Native lifeforms:** Varying plant and animal life, rarely sentient: suitable for colonization
	+ **Example:** Indri VIII
* **Class-M:** Minshara-type planet
	+ **Age:** 3-10 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Surface water abundant; if water or ice covers more than 80% of surface, plant is considered O or P-Class
	+ **Atmosphere:** Primarily oxygen and nitrogen, sometimes other gases
	+ **Native lifeforms:** Varying plant and animal life, often sentient; suitable for colonization
	+ **Example:** Earth, Orum, Vulcan, Cardassia, Kzin, Sangheilios, Janjur Qom, Doisac, Palaven, Sur'Kesh, various others
* **Class-N:** Reducing planet
	+ **Age:** 3-10 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** High surface temperature due to greenhouse effect, water exists only as vapor
	+ **Atmosphere:** Extremely dense, carbon dioxide and sulfides
	+ **Native lifeforms:** Unknown
	+ **Example:** Venus
* **Class-O:** Pelagic planet
	+ **Age:** 3-10 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Liquid water covers 80% or more of surface area
	+ **Atmosphere:** Nitrogen, oxygen, trace elements
	+ **Native lifeforms:** Varying plant and animal life, often sentient
	+ **Example:** Andoria, Kahje, Alonis, Argo
* **Class-P:** Glaciated planet
	+ **Age:** 3-10 billion years
	+ **Diameter:** 10,000-15,000 km
	+ **Orbital zone:** Ecosphere
	+ **Surface conditions:** Water ice covers 80% or more of surface area
	+ **Atmosphere:** Nitrogen, oxygen, trace elements
	+ **Native lifeforms:** Hardy plant and animal life, rarely sentient
* **Class-Q:** Variable planet
	+ **Age:** 2-10 billion years
	+ **Diameter:** 4,000-15,000 km
	+ **Orbital zone:** Hot zone/ecosphere/cold zone
	+ **Surface conditions:** Ranges from molten to water and/or carbon dioxide ice, due to eccentric orbit or variable output of star
	+ **Atmosphere:** Ranges from tenuous to very dense
	+ **Example:** Genesis
* **Class-R:** Rogue terrestrial planet/dwarf planet/planetoid
	+ **Age:** 2-10 billion years
	+ **Diameter:** 1,000-15,000 km
	+ **Orbital zone:** Interstellar space, cometary halos
	+ **Surface conditions:** Varying; may be temperate due to geothermal heating
	+ **Atmosphere:** Varying, from nonexistent to volcanic outgassing
	+ **Example:** Dakala
* **Class-Y:** Demon planet
	+ **Age:** 2-10 billion years
	+ **Diameter:** 10,000-50,000 km
	+ **Orbital zone:** Hot zone/ecosphere/cold zone
	+ **Surface conditions:** Temperatures can exceed 500 °K
	+ **Atmosphere:** Turbulent, saturated with toxic chemicals and thermionic radiation