Eris (dwarf planet)
On the 5th of January 2005, a team led by Mike Brown at Palomar Observatory announced the discovery of Eris. The object had actually been captured in images taken on the 21st of October 2003, but its slow motion across the sky caused automated software to discard it. The system excluded any object moving slower than 1.5 arcseconds per hour to reduce false positives. When Sedna was found later that year, it moved at 1.75 arcsec/hour, prompting the team to re-examine their old data with a lower speed limit. They manually sorted through previously rejected frames and found Eris in January 2005. The announcement came on the 29th of July 2005, coinciding with reports about other large trans-Neptunian objects. Precovery images were eventually traced back to the 3rd of September 1954, showing the object decades before its official recognition.
The Caltech team proposed the name Eris on the 6th of September 2006, after an unusually long period where the object carried the provisional designation 2003 UB313. Before this decision, the public knew it as Xena, an informal nickname inspired by the television series Xena: Warrior Princess. Brown had reserved the name Xena for the first body larger than Pluto. He initially wanted to call the object Lila, referencing a Hindu concept of cosmic play and honoring his newborn daughter. His personal webpage listed /~mbrown/planetlila, but he forgot to update it during the chaos surrounding Haumea's discovery. The name Persephone was also considered but rejected because minor planet 399 already bore that title. The IAU accepted Eris on the 13th of September 2006. NASA adopted the Hand of Eris symbol from Discordianism, while Moscow State University used a variation resembling the all rights reversed symbol.
NASA initially described Eris as the Solar System's tenth planet following its discovery in 2005. This classification created uncertainty about how many planets existed in our solar system. The International Astronomical Union formed a group to define the term planet precisely. On the 24th of August 2006, they approved a new definition that reclassified both Eris and Pluto as dwarf planets. This decision reduced the number of known planets to eight, matching the count before Pluto's discovery in 1930. Brown later stated his approval of this classification. The IAU added Eris to its Minor Planet Catalogue with the designation (136199) Eris. The redefinition addressed ongoing debates about whether Pluto should remain classified as a planet given the discovery of similarly sized objects like Eris.
Eris has an orbital period of 561 years with an aphelion of 97.7 astronomical units and a perihelion of 38.4 AU. Its orbit is highly inclined at approximately 44 degrees relative to the ecliptic plane. Numerical integration by JPL Horizons shows it reached perihelion around 1699 and will return on the 6th of December 2257. As of 2007, Eris had an apparent magnitude of 18.7, making it detectable by some amateur telescopes. A stellar occultation event in November 2010 provided preliminary data suggesting Eris was smaller than previously thought. Final results announced in October 2011 estimated its diameter at 2,326 kilometers. This made Eris slightly smaller than Pluto but more massive. Based on Dysnomia's orbital period of 15.774 days, scientists calculated Eris to be 27% more massive than Pluto. The density of 2.43 grams per cubic centimeter indicates substantial rocky composition.
Spectroscopic observations from the 25th of January 2005, using the Gemini North Telescope revealed methane ice on Eris's surface. Infrared light showed similarities to Pluto and Neptune's moon Triton. Near-infrared spectroscopy by the James Webb Space Telescope in 2022 detected deuterated methane ice with lower abundances than Jupiter-family comets like 67P/Churyumov, Gerasimenko. Substantial quantities of nitrogen ice were also found, estimated at one-third the volume of methane. Unlike Pluto's reddish surface, Eris appears almost white and uniform due to methane condensation covering any tholin deposits. Surface temperature varies between approximately -240°C and -228°C. Methane and nitrogen can sublime to form a temporary atmosphere when Eris approaches closer to the Sun. Spectroscopic data supports the idea that the surface is continually refreshed through radiogenic convection or glacial movement similar to Pluto's Sputnik Planitia.
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Common questions
When was the dwarf planet Eris officially announced by Mike Brown?
The team led by Mike Brown at Palomar Observatory announced the discovery of Eris on the 5th of January 2005. The object had actually been captured in images taken on the 21st of October 2003, but its slow motion across the sky caused automated software to discard it.
What date did the IAU accept the name Eris for the dwarf planet?
The International Astronomical Union accepted the name Eris on the 13th of September 2006. Before this decision, the public knew the object as Xena, an informal nickname inspired by the television series Xena: Warrior Princess.
On what day were both Pluto and Eris reclassified as dwarf planets?
The International Astronomical Union approved a new definition that reclassified both Eris and Pluto as dwarf planets on the 24th of August 2006. This decision reduced the number of known planets to eight, matching the count before Pluto's discovery in 1930.
How does the mass of Eris compare to the mass of Pluto?
Scientists calculated Eris to be 27% more massive than Pluto based on Dysnomia's orbital period of 15.774 days. Final results announced in October 2011 estimated its diameter at 2,326 kilometers, making Eris slightly smaller than Pluto but more massive.
When will the dwarf planet Eris return to perihelion after reaching it around 1699?
Numerical integration by JPL Horizons shows that Eris reached perihelion around 1699 and will return on the 6th of December 2257. The object has an orbital period of 561 years with an aphelion of 97.7 astronomical units and a perihelion of 38.4 AU.