Eris
Dwarf Planet· orbits the Sun
Eris is the most massive known dwarf planet — slightly heavier than Pluto — orbiting in the scattered disc far beyond the Kuiper belt. Its 2005 discovery prompted astronomers to formally define 'dwarf planet'. It has one moon, Dysnomia. Surface temperature is estimated near 30 K.
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Key facts
Mass
1.66 × 10²² kg
0.226 Moon masses
Radius
1,163 km
18% of Earth's radius
Surface gravity
0.819 m/s²
8% of Earth's gravity
Day length
15.8 days
Year
560 Earth years
204,365 Earth days
Distance from Sun
67.9 AU
Moons
1
Dysnomia
Science
Physical
- Mass
- 1.66 × 10²² kg · 0.226 Moon masses
- Radius
- 1,163 km · 18% of Earth's radius
- Density
- 2,519 kg/m³ · 2.5× water
- Computed from mass and radius
- Surface gravity
- 0.819 m/s² · 8% of Earth's gravity
- Computed from mass and radius
- Escape velocity
- 1.38 km/s · 12% of Earth's escape velocity
- Computed from mass and radius
Orbital
- Distance from the Sun
- 95.5 AU
- Computed from the position at the selected time
- Semi-major axis
- 67.9 AU
- Computed from the cached state vector
- Eccentricity
- 0.4389
- Computed from the cached state vector
- Inclination
- 64.08 °
- Computed from the cached state vector
- Orbital period
- 559.52 years
- Computed from the cached state vector
- Perihelion
- 38.1 AU
- Computed from the orbital elements
- Aphelion
- 97.7 AU
- Computed from the orbital elements
- Mean orbital velocity
- 3.61 km/s
- Computed from the orbital elements
Rotation
- Rotation period
- 15.8 days
Composition
- Bulk composition
- A highly reflective surface of methane and nitrogen ices over a large rocky interior, inferred from spectroscopy and a high bulk density (~2.4 g/cm³). The deep interior is unconstrained — no spacecraft has visited.
- Surface imagery
- No real surface imagery exists — this object has never been visited; color is approximate, inferred from spectroscopy.
Radiation & temperature
- Insolation
- 0.000217 S⊕ · 1/4,610 of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
- Geometric albedo
- 0.96
- V-band geometric albedo ≈ 0.96 — among the most reflective bodies known; Bond albedo not directly measured.
- Equilibrium temperature
- 15 K (-258 °C)
- Computed from albedo + distance from the Sun (airless black body); uses the geometric albedo as an estimate
Discovery & history
- Discovered
- January 5, 2005
- By
- Mike Brown, Chad Trujillo and David Rabinowitz
- Method
- Photographic plates
- Name
- The Greek goddess of strife and discord — apt, given the controversy it caused.
Eris was found in 2005 in images from Palomar Observatory and, being more massive than Pluto, forced astronomers to decide what counts as a planet. The result was the IAU's 2006 definition that demoted Pluto and created the 'dwarf planet' category. Eris, in the scattered disc far beyond Neptune, has a moon, Dysnomia, and one of the most reflective surfaces in the Solar System.
Images
Images from open archives · credit shown per image