Image Credit & Copyright: NASA/ESA Hubble Space Telescope.

Discovered on January 5, 2005 by Mike Brown (AKA Pluto Killer) and his team of Chad Trujillo and David Rabinowitz from the California Institute of Technology (Caltech) discover minor planet 136199 Eris at the far reaches of the outer solar system.  No big deal right?  Well that’s until you start to discover a few things about it that get your attention not to mention the naming facts are really fun.  Let’s have a look.

First off it’s a sphere so that means it’s big enough to have undergone hydrostatic equilibrium which is what creates spheres out of anything in space with enough mass.  Upon further investigation it was realized that Eris is actually bigger than Pluto and almost 30% more massive making it the largest of the dwarf planets and the 9th largest solar system body to orbit the Sun.

Its orbit is another story all together.  A year on Eris is 558 Earth years or to put it another way; it takes Eris 558 Earth years to make one orbit of the Sun as it traverses a wildly elliptic orbit.  Its semi-major axis or average distance to the Sun is about 68 astronomical units (AU).  That’s 69 times the distance from the Sun to the Earth.  At its closest (perihelion) it reaches 38 AU which crosses the orbit of Pluto.  The last time this happened was in 1698 and will occur again around 2257. In roughly 800 years it won’t just cross the orbit of Pluto; it will actually be closer to the Sun than Pluto for a time.  At its most distant (aphelion) it stretches to 97.6 AU which is three times further away than Pluto.  The last time this happened was in 1977.  Its orbit is also highly inclined, almost 44 degrees to the ecliptic.

Originally cataloged as 2003 UB313 and minor planet 136199 the team named this object Xena after “Xena: Warrior Princess” which allowed for a name that leads with an “X” for planet “X” or the tenth planet.  This was more of a fun name the team kept to themselves while awaiting an official International Astronomical Union (IAU) name which came on September 13, 2006.  Eris; the Greek goddess of chaos, strife and discord.  Keeping in line with the dark names of some of the outer solar system bodies like Pluto and its moons.

Eris also has a moon; Dysnomia, with an orbital period of 16 days.  Of course the Caltech team had an initial name for that as well; Gabrielle after Xena’s sidekick on the television show.  The IAU handed down the official name of Dysnomia; the daughter of Eris and the Greek goddess of lawlessness.  Lawlessness…what was the actresses last name that played Xena on the television show? (mic drop)

NAME?: Eris, 136199 Eris, S/2005 (2003 UB313), or Xena & moon, Dysnomia, S/2005 (2003 UB313), Gabrielle.

WHAT IS IT?: Dwarf planet, Kuiper Belt Object (KBO).

HOW BIG IS IT?: 2326 km or 1445 mi. in diameter and 27% more massive than Pluto.

HOW FAR AWAY IS IT?: Average distance from the Sun is 67.8 AU with a perihelion of 38 AU and an aphelion of 97.6 AU.  That’s closer to the Sun than Pluto at its perihelion and more than 3 times more distant at its aphelion.


DISCOVERY: January 5, 2005 by Mike Brown and team from Caltech.

ORBITAL PERIOD: 558 years.

MOONS: Dysnomia, formerly S/2005 (2003 UB313) and Gabrielle.  It has an orbital period of 16 days.

NASA Hubblesite News Center page for this image:

Mike Brown’s Planets:

Mike Brown Twitter:

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