Eris

Eris (catalog designation 136199 Eris) is a small dwarf planet that orbits the Sun in a region far beyond Neptune. It is one of the largest known objects beyond Neptune's orbit and is comparable in size to Pluto.

The discovery of Eris in the mid-2000s prompted astronomers to reconsider the definition of the term 'planet'. The International Astronomical Union (IAU) issued a new definition in 2006, which placed both Pluto and Eris in the category of 'dwarf planet'.

Discovery and naming

Eris was identified from telescope observations made in California by a team led by astronomer Mike Brown. The name comes from Eris, the Greek goddess of discord in ancient mythology. This name was considered fitting given the scientific debate surrounding the definition of a planet.

Orbit and characteristics

Eris has a highly elliptical orbit, which means the distance between it and the Sun varies considerably. It takes many centuries to complete one orbit. Its surface is described as very bright, suggesting that it is covered by frozen gases.

The moon Dysnomia

Eris has a moon called Dysnomia. Observations of this moon's orbit have made it possible to calculate Eris's mass with precision, which is why Eris is known to be more massive than Pluto despite having a similar diameter.