Definition
A dwarf planet is a type of celestial object that orbits a star and has sufficient mass for its gravity to shape it into a nearly spherical form (hydrostatic equilibrium). Unlike planets, it has not cleared other bodies sharing its orbital zone. It is not a natural satellite of another body.
Orbital characteristics
Dwarf planets follow orbits around their primary star, sometimes highly eccentric or inclined. Their trajectory may take them through or near regions with small bodies such as the asteroid belt or the Kuiper Belt. Their orbital stability is ensured by their own mass and interactions with nearby bodies.
Internal structure
The internal structure of dwarf planets varies with their composition. Some are rocky with a differentiated core, others partly icy or composed of mixed materials. Their modest size often limits full differentiation, but several show signs of past geological activity.
Environment and companions
Some dwarf planets have natural satellites, sometimes multiple. They may be surrounded by rings, a thin atmosphere, or a dusty environment. Their gravitational interaction with other small bodies is limited, which distinguishes them from dominant planets.
Classification and status
Dwarf planets form an intermediate category between classical planets and small bodies. Their recognition is based on criteria of shape, orbit, and mass. The status of an object as a dwarf planet depends on the evolution of astronomical classification criteria.