Eris

Eris (minor-planet designation: 136199 Eris) is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-
Neptunian object (TNO) in the scattered disk and has a high-eccentricity orbit. Eris was discovered in January 2005 by a Palomar Observatory–based team led by Mike Brown and verified later that year. It was named in September 2006 after the Greco–Roman goddess of strife and discord. Eris is the ninth-most massive known object orbiting the Sun and the sixteenth-most massive overall in the Solar System (counting moons). It is also the largest known object in the solar system that has not been visited by a spacecraft. Eris has been measured at 2,326 ± 12 kilometres (1,445 ± 7 mi) in diameter; its mass is 0.28% that of the Earth and 27% greater than that of Pluto, although Pluto is slightly larger by volume. Both Eris and Pluto have a surface area that is comparable to that of Russia or South America.
Discovery 	Discovery 	 	 	 	
Discovered by 	
* M. E. Brown
* C. A. Trujillo
* D. L. Rabinowitz	 	 	 	
Discovery date 	January 5, 2005 	 	 	 	
Designations 	Designations 	 	 	 	
MPC designation 	(136199) Eris 	 	 	 	
Pronunciation 	/ˈɛrɪs/, /ˈɪərɪs/ 	 	 	 	
Named after 	Ἔρις Eris 	 	 	 	
Alternative designations 	2003 UB313
Xena (nickname)	 	 	 	
Minor planet category 	
* Dwarf Planet 	 	 	 	
Adjectives 	Eridian 	 	 	 	
Symbol 	(Mostly astrological) 	 	 	 	
Orbital characteristics 	Orbital characteristics 	 	 	 	
Epoch May 31, 2020
(JD 2459000.5)	Epoch May 31, 2020
(JD 2459000.5)	 	 	 	
Earliest precoverydate 	September 3, 1954 	 	 	 	
Aphelion 	97.457 AU(14.579 Tm) 	 	 	 	
Perihelion 	38.271 AU (5.725 Tm) 	 	 	 	
Semi-major axis 	67.864 AU (10.152 Tm) 	 	 	 	
Eccentricity 	0.43607 	 	 	 	
Orbital period (sidereal) 	559.07 yr (204,199 d) 	 	 	 	
Average orbital speed 	3.434 km/s 	 	 	 	
Mean anomaly 	205.989° 	 	 	 	
Mean motion 	0° 0m 6.307s / day 	 	 	 	
Inclination 	44.040° 	 	 	 	
Longitude of ascending node	35.951° 	 	 	 	
Time of perihelion 	≈ December 1, 2257
±11 days	 	 	 	
Argument of perihelion 	151.639° 	 	 	 	
Known satellites 	1 (Dysnomia) 	 	 	 	
Physical characteristics 	Physical characteristics	 	 	 	
Mean diameter 	2326±12 km 	 	 	 	
Mean radius 	1163±6 km 	 	 	 	
Surface area 	(1.70±0.02)×107 km2 	 	 	 	
Volume 	(6.59±0.10)×109 km3 	 	 	 	
Mass 	
* (1.6466±0.0085)×1022 kg(system)
* (1.638±0.014)×1022 kg(Eris only)
* 0.0027 Earths; 0.22 Moons	 	 	 	
Mean density 	2.43±0.05 g/cm3 	 	 	 	
Equatorial surface gravity 	0.82±0.02 m/s2
0.084±0.002 g	 	 	 	
Equatorial escape velocity 	1.38 ± 0.01 km/s 	 	 	 	
Sidereal rotation period 	15.786 d(synchronous) 	 	 	 	
Axial tilt 	≈ 78.3° to orbit (assumed)
≈ 61.6° to ecliptic(assumed)	 	 	 	
Geometric albedo 	0.96+0.09
−0.04 [sic] geometric
0.99+0.01
−0.09 Bond	 	 	 	
{| class="fandom-table" 	
{| class="fandom-table"	Surface temp.	min 	mean	max
(approx) 	30 K 	42 K 	56 K	 	
Eris has one large known moon, Dysnomia. In February 2016, Eris's distance from the Sun was 96.3 AU (14.41 billion km; 8.95 billion mi), more than three times that of Neptune or Pluto. With the exception of long-period comets, Eris and Dysnomia were the most distant known natural objects in the Solar System until the discovery of 2018 AG37 and 2018 VG18 in 2018.
Because Eris appeared to be larger than Pluto, NASA initially described it as the Solar System's tenth planet. This, along with the prospect of other objects of similar size being discovered in the future, motivated the International Astronomical Union (IAU) to define the term planet for the first time. Under the IAU definition approved on August 24, 2006, Eris, Pluto and Ceres are "dwarf planets", reducing the number of known planets in the Solar System to eight, the same as before Pluto's discovery in 1930. Observations of a stellar occultation by Eris in 2010 showed that it was slightly smaller than Pluto,which was measured by New Horizons as having a mean diameter of 2,377 ± 4 kilometres (1,477 ± 2 mi) in July 2015.