Eris Worksheets

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Key Facts & Information

  • Eris is the most distant dwarf planet which is located beyond the orbit of Neptune. It is the second-largest dwarf planet discovered, and it caused Pluto and it to be reclassified from planet to dwarf planet.
  • It was first discovered in 2005 as a planet. It is the same size as Pluto and three times further than the Sun.
  • Mike Brown’s team of astronomers discovered Eris while they were analyzing some pictures that were taken in 2003.
  • It was publicly announced in 2005. It caused problems because it was first thought that Eris was bigger than Pluto. It triggered a debate that led to the decision of the  IAU to clarify the definition of planet in 2006. Now, Eris and Pluto are considered as dwarf planets.
  • Xena is the informal name of Eris used internally by the discovery team. This name was already saved to be used by the time they discovered an object that would be bigger than Pluto.
  • The names Eris was decided on in 2006. Like the other planets, it deserved to be given a name which comes from Greek or Roman mythology because it was known as a planet for a long time.
  • Eris is the goddess of strife and discord. It symbolically represented the discord in the astronomical community caused by the debate over their classification.


  • Eris is a member of objects that orbit in a disc-like zone beyond the orbit of Neptune called the Kuiper Belt and Eris is the only dwarf planet that orbits it.
  • The faraway realm is covered with miniature icy worlds formed early in the history of our Solar System about 4.5 million years ago.

Distance, Size & Mass

  • Eris is about 68 AU away from the Sun, and currently 95.1 AU from the Earth. It takes about 13 hours for light to travel from Eris to us.
  • It has a radius of about 722 mi or 1,163 km, which makes it ⅕ of the Earth’s radius.
  • It is also a bit smaller than our moon, like Pluto. If Earth is a nickel, Eris would be a popcorn kernel. It has a diameter of 2,326 km or 1,445 mi.
  • It is slightly smaller than Pluto, but Eris is 27% more massive and denser. Eris has been placed as the 10th largest object to orbit the Sun and remains the 9th largest by mass.

Orbit & Rotation

  • It takes about 558 years for Eris to make one trip around the Sun. It completes one rotation every 25.9 hours. Its maximum distance from the Sun is 97.65 AU and the minimum distance is at 37.91 AU. Its orbit is highly inclined and tilted at about 44 degrees to the ecliptic. It is estimated that in 800 years, it will be closer to The Sun than Pluto.

Structure, Surface & Atmosphere

  • Eris has an estimated albedo of 0.96 which is higher than any other large body in the Solar System, except for Enceladus, the sixth-largest moon of Saturn.
  • It has a high albedo because of its surface ices that are being replenished due to the temperature fluctuations as Eris’ eccentric orbit takes it closer and farther from the Sun.
  • It has a density of 2.52±0.07 g/cm3, it is believed that it is largely composed of rocky materials. It is suggested to have an internal ocean of liquid water at the mantle-core boundary due to the internal heating via radioactive decay.
  • Methane ice is present in Eris, which indicates that its surface is very similar to Pluto and Triton, the largest moon in Neptune. Its eccentric orbit is also one of the factors that makes its surface temperature between -243.2 and -217.2 celsius. Pluto and Triton have reddish surfaces, while Eris has white. 
  • Eris is three times farther away from the Sun than Pluto. It approaches close enough to the Sun that some of the ices on the surface might warm enough to sublime.
  • Methane is a highly volatile substance. Its presence shows either that Eris has always resided in the distant reaches of the Solar System, where it is cold enough for methane ice to exist, or, it can also be that the celestial body has an internal source of methane to replenish gas that escapes from its atmosphere.


  • Eris has one satellite moon discovered in 2005 which was named as Dysnomia after the daughter of the goddess Eris.
  • It was first named as Gabrielle, the sidekick of Xena, a warrior princess in a TV show.
    • It is the second-largest moon of a dwarf planet. The first-largest moon is Pluto’s, which is called Charon. It was discovered after the adaptive optics team in Hawaii carried out observations using a newly commissioned laser guide star adaptive optic system.
    • It believed to be made completely out of ice. Its diameter is at around 700 +/-115 km. It has as, albedo of 0.04+0.02/-0.01 and a semi-major axis of 37,460 km / 23,276 mi. Its circular orbit lasts about 16 days. It has a very dark colored surface compared to Eris.

Life Habitability

  • It seems unlikely that life could exist here due to the extremely cold temperatures.

Did You Know?

  • Eris is currently located in the Cetus Constellation and will enter the Pisces Constellation in 2036.
  • It is about ⅔ of the Moon’s diameter and ⅓ of its volume, which means all of the objects in the Asteroid Belt could fit inside it.
  • Eris has a surface size similar to that of Russia.
  • Standing on Eris will make you feel 11 times lighter because its gravity is 11 times weaker than that of Earth. Even if it has a weaker gravity than the Earth, it has the strongest gravity out of all the dwarf planets with 0.82m/s2.
  • If a person could stare at the sky from Eris, they would have a sharp view of the Milky Way and the stars, since atmosphere can’t get in the way. The most spectacular view would be that of Dysnomia, its moon, which is pretty close to Eris.
  • Eris’ moon orbits ten times closer its parent planet than the Earth’s moon.