Eris

Eris is the biggest known dwarf planet in the solar system. It is about the same size as Pluto but three times farther from the Sun.

When discovered, Eris appeared to be larger than Pluto. This triggered a debate in the scientific community that led to the dwarf planet definition change in 2006. Pluto, Eris and similar objects are now classed as dwarf planets due to this change.

Originally being designated the name 2003 UB313 (and nicknamed for the television warrior Xena by the discovery team), Eris is named after the Greek goddess of discord and strife.

## Exploration

Eris was first spotted by Mike Brown, Chad Trujillo and David Rabinowitz during the Palomar Observatory survey of the outer solar system.

## Discovery

Eris was discovered on October 21, 2003 at the Palomar Observatory by M.E. Brown, C.A. Trujillo and D. Rabinowitz.

## Size and Distance

With a radius of 722 miles (1,163 kilometres), Eris is 1/5 the radius of Earth. Eris is a little bit smaller than Earth's moon along with Pluto. Eris would be the size of a popcorn kernel if Earth were a nickel.

Eris is 68 astronomical units away from the Sun, with an average distance of 6,289,000,000 miles (10,125,000,000 kilometres). One astronomical unit (abbreviated as 'AU') is the equal distance from the Sun to Earth. Sunlight takes more than nine hours to travel to Eris from this distance.

## Orbit and Rotation

A year on Eris takes 557 Earth years (the time it takes to complete on trip around the Sun). Eris' orbit is way out of the plane of the solar system's planets and extends farther than the Kuiper Belt, a disc-like zone beyond Neptune.

During Eris' orbit, the dwarf planet completes one rotation every 25.9 hours, making its dy-length very similar to ours.

## Formation

Eris is part of a group of objects that sit in a disc-like zone beyond the orbit of Neptune called the Kuiper Belt. This realm is populated with thousands of miniature icy worlds which formed in the early history of our solar system, about 4.5 billion years ago. These objects are called Kuiper Belt objects, transneptunian objects or plutoids.

## Structure

Scientists know very little about Eris' internal structure.

## Surface

Eris has a rocky surface similar to Pluto. Scientists think temperatures can reach to -243 degrees celsius.

## Atmosphere

Eris is so far from the Sun that it can its atmosphere could freeze and collapse, thus resulting in snow. As the dwarf planet reaches closer to the Sun, the atmosphere thickens.

## Magnetosphere

Scientists know nothing about Eri's magnetosphere.

## Moons

Eris has one very small moon in its orbit, Dysnomia. It has a orbit that lasts 16 days and has a circular orbit. The moon is named after Eris' daughter, the demon goddess of lawlessness

Moons like Dysnomia allow astronomers to calculate the mass of the parent. Dysnomia plays a key role in determining how Eris and Pluto are alike.

## Human Life

Eris' surface is extremely cold so it's very unlikely for any life form to adapt to it.

## Significant Dates

**8 January 2005** - Scientist use images from ground telescopes and announce they have discovered a Pluto-like world billions of miles beyond Neptune. They nickname the discovery Xena after a TV fictional character. The discovery builds up a huge debate about what should be classed as a planet.

**September 2005** - Scientists announce Xena has a small moons in its orbit, which they give the name Gabriella (Xena's sidekick on a show about a warrior princess).

**26 August 2006** After months of debate, the International Astronomical Union votes to change the definition of a planet. The new ruling system classifies Pluto, Haumea, Makemake, Ceres and Eris as a dwarf planet.

**14 September 2006** - The IAU (International Astronomical Union) announces that the new discovery, Xena, will now be known as Eris. The small moon is renamed to Dysnomia. This is fitting since the demotion of Pluto continued the debate of why Pluto is no longer a planet.