Facts About Eris - The Most Massive Dwarf Planet


Eris (centre) with its moon Dysnomia (left)
Eris (centre) with its moon Dysnomia (left)

Eris is the most massive and second-largest dwarf planet in the solar system. It is named after the Greek goddess of chaos, strife and discord. When discovered, Eris and its moon was the most distant known object in the solar system. Distant than three times of Pluto's distance from the Sun, it is located in a cold region beyond Neptune known as the scattered disk. With a diameter little more than the width of the half of the United States, it is the tenth-largest object that is in direct orbit to the Sun.

Eris Profile

Name Eris
Known Satellite 1
Distance from Sun (avg) 10.125 billion km (68 AU)
Radius 1163±6 km
Volume 6.59 × 109 km3
Mass 1.66 × 1022 kg
Surface area 17 million km2
Gravity 0.82 m/s2
Max Temperature -217℃ or -358°F
Min Temperature −243°C or -405°F
Length of day 25.9 hours
Length of year 559 Earth days
Discovered on January 5, 2005

Quick Facts About Eris

  1. Eris is the largest object in the solar system that has not been visited by spacecraft.
  2. Eris will be closer to the sun than Pluto in roughly 800 years.
  3. The atmosphere is highly variable. When it is farther from the sun, its atmosphere freezes and fall like snow on earth.
  4. When it is at its closest point to the sun, the atmosphere converts back into gas.
  5. The sunlight takes more than nine hours to reach Eris.
  6. Its day-length similar to our Earth that is 25.9 hours.
  7. Its surface is highly reflective, which makes it the second most reflective body in the solar system after Saturn's moon Enceladus.
  8. The surface can reflect 96% of the light that hits its surface, which enables it to be seen through amateur telescopes.
  9. It is the ninth most massive body that is directly revolving around the Sun.
  10. Eris is 27% more massive than Pluto, making it the most massive dwarf planet.
  11. After its classification as a minor planet, its new designation is 136199 Eris.

Detailed Facts About Eris

  • Eris was once recognised as the tenth planet

Samuel Oschin telescope - Telescope that was used to discover Eris
Samuel Oschin telescope - Telescope that was used to discover Eris 
© Wikimedia

A team of Mike Brown, Chad Trujillo, and David Rabinowitz were searching for objects in the outer solar system. They discovered Eris On January 5, 2005, after re-analyzing images taken on October 21, 2003, at Palomar Observatory. After completing observations and calculation, the discovery was officially announced with another dwarf planet Makemake on July 29, 2005.

Though, initially, Eris appeared to be larger than Pluto, so NASA considered it as the tenth planet (after Pluto). After the discovery of similar objects, IAU re-classified it along with other objects which have similar characteristics as a dwarf planet in 2006.
  • Eris had the nickname "Xena"

Eris - Godess of strife and discord
Eris - goddess of strife and discord

Since its discovery in 2005, the discovery team gave it an informal name Xena after the title character of the television series Xena: Warrior Princess. The team did not confirm whether the planet would be classified as a planet or a small planet, so they used to call it as Xena until its classification. However, this name became very popular among the public.

On September 6, 2006, Michael E. Brown, a member of the discovery team, suggested the name Eris after the Greek goddess of strife and discord. Seven days after the proposal, on September 13, 2006, IAU declared the name Eris as the official name for the planet. The reason behind the name was that Eris had been recognised as the planet, so Brown thought that a name from Greek or Roman mythology should be given to it as other planets have.
  • Eris was once considered larger than Pluto

Image of Eris that was used to measure its size captured by Hubble telescope
Image of Eris that was used to measure its size captured by Hubble telescope 

When the Eris was first discovered, due to its higher reflective surface than Pluto, the discoverer thought that it was larger than Pluto. Further in December, Hubble telescope measured it for the first time. It detected its diameter to be nearly 2,397 km or 1,490 miles, which is slightly larger than Pluto.

The team then measured it again by observing a stellar occultation in Nov 2010. In the stellar occultation, they observed Eris passing in front of a star. So by calculating the time taken by it to pass in front of the star can give a more precise data of its size. The occultation provided the diameter of 2,336 km or 1,451 miles with a plus or minus of 12 km or 7 miles.
  • Eris has a small moon

Artist's impression of Eris and its moon Dysnomia
Artist's impression of Eris and its moon Dysnomia
© Wikimedia

In September 2005, a team at the Keck telescopes in Hawaii discovered the only known moon of Eris - Dysnomia by utilising the newly made laser guide star adaptive optics system. The diameter of Dysnomia is estimated to be about 700 km with a plus or minus of 115 km. Its shape is harder to detect because it is much fainter than Eris. However, it is envisaged that to be spherical in shape due to its large size as the three ellipsoidal moons of Saturn and Uranus have.

Brown suggested the name Gabrielle for the newly found moon, after the sidekick of Xena in the serial. Later IAU gave Eris its official designation, Brown suggested name "Dysnomia" for the moon, after Eris's daughter who was the Greek goddess of lawlessness. The primary reason behind the name was that he wanted to give it a name that is similar to her wife's name, Diane.
  • Eris is located in an extremely dark and cold region

Objects in the outer solar system
Objects in the outer solar system
© Wikimedia

Eris is the largest member of the scattered disk that is located far beyond the Kuiper belt. The small icy objects in both of the discs are the leftover after the formation of planets. The objects in the scattered disk have a highly eccentric orbit. They can come close as 30 AU to the sun and can go far as 100 AU. The highest possible temperature on Eris is estimated to about -217 °C or -359 °F that can be drop to -243 °C or -405 °F.
  • Eris also has a highly eccentric orbit

Orbit of Eris
Orbit of Eris
© Wikimedia

Eris completes its orbit with an orbital period of 559 earth years. The orbit takes it to 37 AU at its closest point to the sun (perihelion) and 97 AU at its farthest (aphelion). Between the year 1698 to 1699, it was closest to the sun and will again return to perihelion approximately in the year 2256 to 2258. The orbit is also highly inclined at 44° rather than plan as earth, and other planets have.

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