Planemo

A **planetary-mass object**, otherwise known as a **planemo** or **world**is a body too small to engage in hydrogen fusion like a star, and is large enough to be in hydrostatic equilibrium and rounded into the shape of a spheroid by its own gravity. The class of planemos includes planets, dwarf planets, round satellites, rogue planets, sub-brown dwarfs, and brown dwarfs. Small objects not in hydrostatic equilibrium and therefore don’t qualify as planemos are called asteroid-class objects (ACOs), which includes asteroids, comets, non-rounded satellites. Objects not in hydrostatic equilibrium yet are round such as Iapetus and Mimas qualify as planemos as an object does not have to be in equilibrium to qualify as a planemo, just large enough to attain equilibrium.

The largest planemo in our solar system is the gas giant Jupiter. The smallest known planemo in our Solar System is Mimas. One of the largest known objects that currently almost makes it as a planemo is the very large asteroid and former planemo Vesta, whose shape is very close to a spheroid and is around the mass required for hydrostatic equilibrium. Vesta, along with many Trans-Neptunian objects are at the border of being considered a planemo due to their mass and possibly round shape.

## **List of Planemos**

The list contains all objects in our Solar System with a radius greater than 150 km, which can function as an estimate for a lower bound to how small planemos can get (although radius is not necessarily a factor in determining planemo status).

### **Inner Solar System**

#### True Planemo

* Mercury (planet)
* Venus (planet)
* Earth (planet)
* Moon (satellite)
* Mars (planet)

#### Gallery

Mercury, a planetVenus, a planetEarth, a planetThe Moon, a satellite and planemoMars, a planet
### **Asteroid Belt**

#### Borderline Planemo

* Vesta (asteroid, former planemo)
* Hygiea (asteroid)

#### Large ACO

* Pallas (asteroid)
* Interamnia (asteroid)
* Europa (asteroid)
* Davida (asteroid)
* Eunomia (asteroid)
* Juno (asteroid)
* Euphrosyne (asteroid)
* Herculina (asteroid)
* Juno (asteroid)
* Cybele (asteroid)
* Psyche (asteroid)
* Patientia (asteroid)
* Bamberga (asteroid)
* Doris (asteroid)
* Egeria (asteroid)
* Iris (asteroid)

#### Gallery

Ceres, an asteroid and dwarf planetVesta, an asteroid and borderline planemoHygiea, an asteroid and dwarf planet candidate
### **Outer Solar System**

#### True Planemo

* Jupiter (planet)
* Io (satellite)
* Europa (satellite)
* Ganymede (satellite)
* Callisto (satellite)
* Saturn (planet)
* Mimas (satellite)
* Enceladus (satellite)
* Tethys (satellite)
* Dione (satellite)
* Rhea (satellite)
* Titan (satellite)
* Iapetus (satellite)
* Uranus (planet)
* Miranda (satellite)
* Ariel (satellite)
* Umbriel (satellite)
* Titania (satellite)
* Oberon (satellite)
* Neptune (planet)
* Triton (satellite)

#### Large ACO

* Hektor (asteroid)
* Hyperion (satellite)
* Phoebe (satellite, former planemo)
* Proteus
* Nereid (satellite)

#### Gallery

Jupiter, a planetSaturn, a planetUranus, a planetNeptune, a planet
### **Kuiper Belt**

#### True Planemo

* Pluto (dwarf planet)
* Charon (satellite)
* Orcus (dwarf planet)
* Salacia (dwarf planet)
* 2002 MS4 (dwarf planet)
* Haumea (dwarf planet)
* Quaoar (dwarf planet)
* Makemake (dwarf planet)

#### Planemo Candidates

* 2003 AZ84 (possible dwarf planet)
* Varuna (possible dwarf planet)
* Varda (possible dwarf planet)
* 2002 AW197 (possible dwarf planet)

#### Large ACO

* Hi'iaka (satellite)
* S/(225088) 1 (satellite)

### **Scattered disc**

#### True Planemo

* Gonggong (dwarf planet)
* Eris (dwarf planet)

#### Planemo Candidates

* Dysnomia (satellite)
* Gǃkúnǁʼhòmdímà (asteroid)

## **References**

1. ↑ https://en.wikipedia.org/wiki/Planet#Planetary-mass\_objects
2. ↑ http://www.polytope.net/hedrondude/worlds.htm