Eris

Eris is a dwarf planet, even further out than Pluto and almost the same size. Its discovery was the reason why Pluto is no longer a planet.

▶ View Eris in the 3D model

Fact file

Type: Dwarf planet
Diameter: 2,326 km
Distance from the Sun: 10,125,000,000 km
Orbital period: 558.1 years
Temperature: -231 °C on average (from -243 to -217 °C)
Mass: 0.0028 Earth masses
Gravity: 0.08 times as strong as on Earth
Escape velocity: 1.4 km/s
Length of day: About 15.8 Earth days
Number of moons: 1

Interesting facts about Eris

Eris is almost as big as Pluto but about 27% more massive – its discovery in 2005 triggered the redefinition of the term “planet” that made Pluto a dwarf planet in 2006.
A year on Eris lasts 558 Earth years; on its strongly elliptical orbit, its distance from the Sun varies between 38 and 98 AU (Earth = 1 AU).
Its surface reflects almost 96% of the sunlight – one of the brightest surfaces in the Solar System. It is named after the Greek goddess of discord, and its moon is called Dysnomia.

Frequently asked questions about Eris

How big is Eris?

Eris has a diameter of 2,326 km. That is about 18% of the diameter of Earth.

How far is Eris from the Sun?

Eris is on average 10.13 billion km from the Sun. That is 67.68 astronomical units (AU). Sunlight takes about 9.4 hours to cover this distance.

How long is a year on Eris?

Eris takes 558.1 Earth years to travel once around the Sun.

How cold or warm is it on Eris?

On Eris the average temperature is −231 °C. The temperature ranges from −243 to −217 °C.

Name and discovery

After the Greek goddess of discord – because its discovery set off the great dispute over Pluto's status as a planet.

Discovered on 5 January 2005 by Mike Brown, Chad Trujillo and David Rabinowitz on images from 2003.

Formation

Eris probably formed closer to the Sun and was flung by the migration of the giant planets onto its present orbit, strongly elliptical and tilted by 44°, in the “scattered disc” beyond the Kuiper Belt.

Atmosphere

Very thin to non-existent; near the Sun, nitrogen and methane could briefly turn to gas and form a wafer-thin atmosphere that later freezes out again.

Exploration

No probe so far; observed with the Hubble telescope, among others, and by a stellar occultation in 2010 that fixed its diameter at about 2,326 km.

Compared with Earth

At 2,326 km across, Eris is about two thirds of the Moon's diameter, but on average almost 68 times further from the Sun than Earth.

Moons of Eris

DysnomiaDysnomia is the only known moon of the dwarf planet Eris, around 600 km across.

Test your knowledge of Eris

Which dwarf planet is about the size of Pluto but even heavier – and was discovered in 2005?

Eris. Eris is about 27% more massive than Pluto. Its discovery led directly to the new definition of a planet.

The full quiz with points and badges is in the 3D model under “Explore”.

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