DWARF PLANET

A dwarf planet is a celestial body that fulfills the following conditions: (a) it orbits about the Sun; (b) it possesses enough mass as so that its own gravity dominates the present forces like rigid body, what implies a form approximately rounded determined by the balance hidrostático; (c) it has not cleaned his orbit of other objects; (d) is not a satellite of a planet. This way, Pluto (overdraft in the year 1930 for C. Tombaugh), Ceres (the first asteroid, found in the year 1801 for G. Piazzi) and Eris (or Éride, identified in 2005 for M. Brown) happens to be dwarf planets. In particular, Pluto loses his status as planet because it does not fulfill one of the characteristics that yes present eight planets of the Solar system: it is not the domineering object in his region of the space or, said otherwise, it has not managed to sweep his orbit, but he shares the area with multitude of other objects of the same type, the bodies that shape the objects belt transneptunianos.

Pluto has turned into the prototype of the plutoides, which would consist of those dwarf planets (therefore, from similar characteristics to those of Pluto) located beyond the orbit of the planet Neptune (which distance is approximately 30 times the one that separates the Earth of the Sun, or 30 astronomical units). This way, the plutoides are dwarf planets transneptunianos. Therefore, Ceres placed in the belt of asteroids (approximately 2.8 au), would not enter inside this category.
At present alone Pluto, Eris, Makemake and Haumea are considered officially plutoides. In principle, any object transneptuniano that has an approximate diameter of approximately 800 km is a candidate for being considered to be a plutoide and a name will be assigned to him as if it was. One hopes that more plutoides should receive names as the science progresses and new discoveries should be realized.

Ceres, a dwarf planet, and Vesta, an asteroid of big size. Both are between the orbits of Mars and Jupiter, in the Belt of Asteroids, where there is located multitude of objects of different masses and forms. Credits: Image of Ceres of J. Parker (NASA, THAT ONE), Vesta's image of L. McFadden (NASA, THAT ONE).

Glossary: "100 basic concepts of Astronomy”