Types of Planet

This page lists the types of planets currently discovered in the Milky Way.

## List

* Carbon Planet - A planet formed largely of carbon in a carbon-rich, oxygen-poor system. Likely to form near the galactic core, or around white dwarfs and neutron/pulsars. Devoid of water, full of carbon dioxide and monoxide smog.

* Chthonian Planet - A former gas giant whose atmosphere has been stripped away due to close proximity to a star.
* Desert Planet - A habitable, terrestrial world with very little water. The habitability zone of desert planets is far larger than traditional garden worlds.
* Double Planet - Two planets who orbit each other.
* Dwarf Planet - A small planet which has not cleared the neighborhood around its orbit. Mass ranges from 0.0001 Earth Masses to 0.1 Earth Masses. Radius ranges from 0.03 Earth radii upwards. Often found in the resonance with the final gas giant of the system. Eccentricity should be less than 0.25 and inclination should be between 10 and 25 degrees.
* Eccentric Jupiter - A Jovian planet with an eccentric orbit.
* Garden World - A habitable terrestrial planet similar to Earth.
* Gas Dwarf - A planet of up to 10 Earth masses composed primarily of hydrogen and helium. Found beyond 1 to 1.2 AU plus the frost line of the system.
* Gas Giant - A massive planet composed primarily of hydrogen and helium. Found beyond 1 to 1.2 AU plus the frost line of a system. Mass ranges from 10 Earth masses to 13 Jupiter Masses (1 Jupiter Mass = 317.8 Earth Masses). Neptune-sized gas giants have a radius of 2-6 Earth radii and Jupiter-sized gas giants have a radius of 6-15 Earth radii. Gas giants above 2 Jupiter Masses will have a radius very close to 1 Jupiter radius (11.209 Earth Masses).
* Hot Jupiter - A Jovian planet of incredible heat due to proximity (between 0.04-0.5 AU) to a star. Eccentricity close to 0.
* Hot Neptune - A Neptune-type planet of incredible heat due to proximity (less than 1 AU) to a star. Eccentricity close to 0.
* Ice Dwarf - An Ice Giant-type planet of up to 10 Earth masses
* Ice Giant - A Uranus/Neptune-type giant planet consisting of far more heavy elements than a Jovian-type planet
* Ice Planet - A planet covered in ice. The existence of life in sub-surface liquid water is possible.
* Iron Planet - An iron-rich terrestrial planet with little or no mantle, such as Mercury
* Lava Planet - A terrestrial planet covered largely in molten lava.
* Ocean Planet - A planet where a significant portion of its mass is made up of water.
* Puffy Planet - A gas giant of low density and large radius. Must be below 2 Jupiter masses. Likely to be closer to the star.
* Super Jupiter: A large gas giant. Found between 0.04 AU and 1 to 1.2 AU plus the frost line of the system.
* Terrestrial Planet - A planet of between 0.1 to 10 Earth masses. Largely composed of rock and metals. Radius less than 1.25 Earth masses (Super Earths may reach 2 Earth radii).

## Worldbuilding Considerations

### Habitability

* Mass between 0.1 and 3.5 Earth masses
* Radius between 0.5 and 1.5 Earth radii
* Surface gravity between 0.4 and 1.6

## Planet Statistics

* Density (p) = M/R^3 (in Earth masses and Earth radii)
* Surface Gravity (g) = M/R^2 = Rp
* Escape Velocity (ev) = sqrt(M/R)
* Circumference = 2piR
* Surface Area = 4piR^2
* Volume = 4/3(piR^3)
* Semi-Major Axis (a) = (q+Q)/2
* Semi-minor axis (b) = asqrt(1-e^2)
* Equation of an ellipse: x^2/a^2 + y^2/b^2 = 1
* Eccentricity (e) : 0 < e < 1
* Periapsis (q) = a(1-e)
* Apoapsis (Q) = a(1 + e)
* Inclination (i) : 0 degrees < i < 180 degrees [0-90 degrees = prograde orbits, 90-180 = retrograde orbits] Should be +-10 degrees of orbital plane
* Ascending and Descending Nodes: the points of intersection of a planetary orbit (orbiting counter-clockwise) with the equatorial plane of a star.
* Longitude of the Ascending Node (@) : 0 degrees < @ < 360 degrees [refers to the angle between the point of reference and the ascending node]
* Argument of Periapsis (w) : 0 degrees < w < 360 degrees [refers to the angle between the periapsis and the ascending node]
* True Anomaly (#) : 0 degrees < # < 360 degrees [refers to the angle between the periapsis and the planet]
* Orbital period (P) = sqrt(a^3/mass of star)

* Orbital velocity (ov) = sqrt(mass of star/R)

## See also

* Artifexian on Orbits
* Orbital Calculator