Eris is the largest dwarf planet in the Solar System, and the ninth largest body orbiting our Sun. Sometimes referred to as the “tenth planet,” its discovery is responsible for upsetting the traditional count of nine planets in our Solar System, as well as leading the way to the creation of a new astronomical category.

fun facts

  • The dwarf planet was named for Eris, the Greek goddess of strife and discord. This is quite fitting, as there was some dispute over the classification when it was discovered. Rejected names for the planet include Xena (from the TV show), Lila, and Persephone (Pluto/Hades’ wife in Greek mythology)
  • Eris has one satellite (moon) which is called Dysnomiaand takes 16 Earth days to complete a full orbit. Dysnomia is named for the daughter of the goddess Eris in Greek mythology and is the Greek goddess of lawlessness.
  • Eris was once considered to become the tenth planet of the solar system before the reclassification of Pluto in 2006. This is due to the large size of Eris, which exceeds Pluto’s mass by 28%.
  • All of the objects inside the asteroid belt, located between the orbits of Mars and Jupiter, could fit inside Eris – even though it is only 2/3 the diameter and 1/3 the volume of Earth’s Moon.
  • Eris is so far from the Sun that its atmosphere sometimes freezes due to lack of sunlight. Over the course of the hundreds of years it takes the dwarf planet to orbit the Sun, it thaws as it gets closer to the Sun’s heat.
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extar facts

Eris was first observed in 2003 during a Palomar Observatory survey of the outer solar system by a team led by Mike Brown, a professor of planetary astronomy at the California Institute of Technology. The discovery was confirmed in January 2005 after the team examined the pictures obtained from the survey in detail.