5th January: Dwarf Planet Eris

Ten years ago today in 2005, Eris, the largest known dwarf planet in the solar system, was discovered. Here are 10 facts about Eris:

1. Eris may be larger than Pluto (we can't be sure as it's apparently very difficult to get an accurate measure of how big such distant planets actually are) and it was initially described as the tenth planet. It was the discovery of Eris that first sparked the debate over the definition of a planet, which led to Pluto being demoted to "dwarf planet" along with Eris.
2. It is thought that Eris was originally an object in the Kuiper Belt which was thrown into its unusual and distant orbit by the gravitational effects of Neptune.
3. It is the most distant known object in the solar system apart from comets and space probes. It is 100 times further from the Sun than Earth is, and three times as far away as Pluto. It is so far away that if a person could stand on its surface and look at the sun, the sun would be no bigger than any other star.
4. It's very cold there. The surface temperature is close to absolute zero, which is about -459ºF or -273ºC.
5. It takes 558 years for Eris to orbit the sun, in a highly eccentric orbit.
6. Eris appears Grey in colour, probably due to the methane ice on its surface. Nothing else is known about the surface of Eris, because no instrument that could observe it has been invented yet.
7. There were a number of alternative names put forward for Eris, and also nicknames. When scientists first suspected there might be another planet there, they referred to it as "Planet X". When they started observing it, but before it could be given an official name, the team nicknamed it "Xena" after TV's warrior princess (whose name conveniently began with X). Why not call it after a TV character, they argued, since Pluto is named after a cartoon! However, convention dictated that a planet must be named for a Greek or Roman deity. Names that were considered were Persephone, Pluto's wife (but there was already an asteroid called that) Lila (a Hindu concept which just happened to sound like the name of the discoverer's daughter). Eris had somehow managed to escape having an asteroid named after her already, so Eris it was.
8. Eris has a moon, Dysnomia, named after the daughter of the goddess Eris. (Moons are usually named after lesser deities associated with the one the planet is named for, hence Jupiter's moons are named after Jupiter's lovers and Saturn's are named after Titans. During the time that Eris was being referred to as "Xena", the moon was appropriately nicknamed "Gabrielle" after Xena the warrior princess's companion. Dysmonia means "lawlessness", and since Xena was played by Lucy Lawless, it seemed especially fitting.)
9. In mythology, Eris is known as a goddess of discord and directly responsible for the Trojan war. Even before this, she was a troublemaker and hence was left off the guest list for the wedding of Peleus and Thetis. Highly offended, Eris decided she would cause trouble anyway, by sending an apple to the party, labelled "for the fairest" which naturally started a fight between Hera, Athena and Aphrodite who all thought the gift was for them. Paris was given the task of deciding which was the most fair goddess. Aphrodite bribed him by promising him the hand of Helen of Sparta, the most beautiful human woman. Helen was already married, but Paris carried her off anyway, which led to the war. Again a fitting name since its discovery sparked off the debate about whether Pluto was a planet or not.
10. The discovery of a new planet is always exciting for western astrologers (western astrology is the only system that accepts new planets) and since the discovery of Eris there has been much discussion about what it means. So far, various astrologers have concluded that Eris represents the development of the feminine to counterbalance the aggression of Mars (Eris's brother); strife, discord, quarrels and battles; rivalry, jealousy, revenge; resourcefulness; keeping a clear head in a crisis; working for happiness; eternal youth and regeneration; genetic sciences and longer life spans.