Eris
Reference data for dwarf planet Eris: 559-year scattered-disc orbit, 2,326 km occultation diameter, 27% greater mass than Pluto, and 0.96 albedo.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Apparent Magnitude (V) | 18.7 mag | ± 0.05 mag | Currently near aphelion at 95.7 AU from the Sun in Cetus. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Sidereal Orbital Period | 204199 d | ± 50 d | Equivalent to 559.1 Julian years. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Semi-Major Axis | 67.864 AU | ± 0.01 AU | JPL Horizons DE440/441 planetary and satellite ephemeris solution | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Orbital Eccentricity | 0.4361 dimensionless | ± 0.0002 dimensionless | Ranges from 38.27 AU at perihelion to 97.46 AU at aphelion, inclined 44.0° to the ecliptic. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mean Radius | 0.1823 R⊕ | ± 0.0009 R⊕ | Stellar occultation chord measurement: 1,163 ± 6 km (diameter 2,326 km; Sicardy et al. 2011). | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
| Mass | 0.00277 M⊕ | ± 0.00003 M⊕ | 1.6466 × 10²² kg (127% of Pluto's mass), derived from the 15.79-day orbit of its moon Dysnomia. | definitive | NASA/JPL Solar System Dynamics & Planetary Fact Sheets |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Eris (136199 Eris) — Scattered-Disc Dwarf Planet at RA 01h 58m 00.00s, Dec -00° 45′ 00.0″ within Cetus, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Identified on January 5, 2005, by Michael Brown, Chad Trujillo, and David Rabinowitz from Palomar Observatory survey images captured in October 2003, 136199 Eris (provisionally nicknamed 'Xena' for 2003 UB313) catalyzed the 2006 International Astronomical Union resolution that created the 'dwarf planet' category. Orbiting in the detached scattered disc with a 44-degree orbital inclination and a 559-year period, Eris currently sits near aphelion roughly 95.7 astronomical units from the Sun—more than three times farther out than Neptune.
Adaptive-optics and Hubble tracking of Eris's 615-kilometer satellite, Dysnomia, across its circular 15.786-day synchronous orbit pinned Eris's mass at 1.65 × 10²² kilograms—27 percent more massive than Pluto. Yet when Eris occulted a faint background star in Cetus in November 2010, chord timings revealed a diameter of 2,326 ± 12 kilometers, slightly smaller than Pluto's 2,377 kilometers. This implies a high rocky-rich bulk density of 2.43 grams per cubic centimeter and a dazzling geometric albedo of 0.96, maintained as a tenuous atmosphere snows fresh methane and nitrogen frost across its ~30 K surface.
Recent precision photometry combined with ALMA thermal measurements of Dysnomia demonstrated that Eris has been tidally braked by its relatively massive moon into a synchronous 15.79-day rotation—matching the Pluto-Charon double-synchronous state.
Practical Visual Observing Guide
- At magnitude V = 18.7 in northern Cetus, Eris is far beyond visual amateur telescopes, except for 24-inch+ instruments under exceptional mountain skies.
- Readily captured in 5-to-15-minute exposures with 8-inch to 14-inch amateur CCD/CMOS astrographs; its slow retrograde opposition motion is ~1.5 arcseconds per hour.
- Moves so slowly across the sky that it spends decades traversing Cetus and Pisces.
Catalog Cross-Identifications & Aliases
Common Aliases: 136199 Eris · 2003 UB313 · Xena
| Catalog Authority | Identifier |
|---|---|
| SIMBAD | Eris |
Related Objects, Comparisons & Guides
Pluto (134340 Pluto) — Kuiper Belt Dwarf Planet
Reference data for Pluto: 247.9-year resonant orbit, 2,376.6 km diameter from New Horizons, Charon binary dynamics, and nitrogen glaciers.
Neptune — Outermost Ice Giant Reference Data
Reference data for Neptune: 164.8-year orbit at 30.07 AU, 17.15 Earth masses, supersonic winds, and Triton observing guide.
Ceres (1 Ceres) — Main-Belt Dwarf Planet Data
Reference data for dwarf planet 1 Ceres: 4.60-year orbit at 2.77 AU, 939.4 km diameter from Dawn, Occator crater salt deposits, and visual magnitude.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Measurement Uncertainty & Optics in Astronomy
How random vs systematic errors, asymmetric error bars, model dependencies, and optical aperture/exit-pupil limits shape astronomical measurements.
Scientific Sources & Dataset Provenance
- NASA/JPL Solar System Dynamics & Planetary Fact Sheets (DE441 (2021/2026)): Park, R. S., et al. 2021, AJ, 161, 105 (The JPL Planetary and Lunar Ephemerides DE440 and DE441) — NASA Jet Propulsion Laboratory / GSFC