The dwarf planet that demoted Pluto was nicknamed Xena
Eris earned its name. Found in 2005 and first hailed by NASA as a tenth planet, it forced astronomers to define the word planet for the first time, and the 2006 ruling demoted Pluto along with it. Its discoverer Mike Brown picked the Greek goddess of strife, noting that this world had stirred up quarrels too.
The discovery nearly slipped past. Brown's team at Palomar Observatory photographed it on 21 October 2003, but their software ignored anything crawling slower than 1.5 arcseconds an hour to cut false alarms. After spotting Sedna moving at 1.75, they lowered the threshold, combed rejected images by eye, and in January 2005 caught Eris creeping against the stars. They meant to wait before going public but rushed the announcement on 29 July 2005, after a Spanish team controversially announced Haumea, another object Brown's group had been tracking, two days earlier. Older images later traced Eris back to 1954.
Naming had to wait for the planet ruling, so the team's joke nickname leaked. Brown had saved Xena, after the television warrior princess, for the first find bigger than Pluto; it began with X, as in Planet X, and sounded mythological. He let it slip to a New York Times reporter who was an old college friend. He had privately liked Lila, after a Hindu concept of the cosmos as a divine game and a homophone of his newborn daughter's name, but dropped it after the web address gave it away. Persephone topped a New Scientist poll but was already taken by an asteroid.
Eris measures about 2,326 kilometres across, a whisker smaller than Pluto, yet it carries 27 percent more mass, worked out from the orbit of its moon Dysnomia. Of all the bodies circling the Sun that no probe has reached, none is larger. Its orbit is tilted about 44 degrees and stretched: one lap takes 558 years, swinging between about 38 and 98 times Earth's distance from the Sun. Its closest approach came around 1699 and its farthest point around 1977; the next close pass is due on 6 December 2257.
For more than a decade Eris and Dysnomia held the title of remotest known natural bodies orbiting the Sun, long-period comets aside, until 2018 VG18 was discovered.
Source: Eris (dwarf planet)
