Why is Eris not a planet?

Answer 1

Even though Eris is spherical, it didn't clear its orbit from other objects.

The classification "dwarf planet" was created because many objects like Eris have been, and are being discovered.

Answer 2

Eris is not a Star as it does not have the required mass or composition to begin Nuclear Fussion turning Hydrogen into Helium. Although it is point of light in the sky it is only the light being reflected back to us from sun, not light of its own making.

Answer 3

The International Astronomical Union (IAU) has identified, and classified, eight planets and five dwarf planets orbiting the Sun (Sol).

Under IAU protocols, both planets and dwarf plants are orbiting bodies that have enough mass to be shaped by their own gravities, however the difference between the two is that dwarf planets have not "cleared" their respective "neighborhoods" of other objects or debris.

At one time Eris was classified as Sol's tenth planet, due to it having a larger mass than Pluto, but since the IAU separated planets from dwarf planets, and Eris shares its orbit with other objects, it has been classified as a dwarf planet. Eris is still considered a major planetary body by the International Astronomical Union, however.

Sol's other dwarf planets are Ceres, Pluto, Haumea and Makemake.

Answer 4

A planet is defined as a rocky

, or gaseous, spherical, celestial body, that orbits the sun, but does not emit its own light. A planet is also considered to be a celestial body that has sufficient mass, therefore, it has its own gravity that overcomes unyielding body forces, and is formed into a hydrostatic equilibrium, or round, shape. It is neither a star nor a satellite of another planet.

A dwarf planet is also a spherical body orbiting the sun; however, to be a dwarf planet, it must be smaller than 3031 miles in diameter, but heavy enough to bear a resemblance to a planet. In addition, a dwarf planet is not big enough to have a distinct orbital path, nor does it orbit another object, like a moon.