Eris is one of the largest known dwarf planets in the Solar System and is located in the scattered disk, a distant and relatively sparsely populated region beyond the Kuiper Belt. Discovered in 2005, Eris has contributed significantly to our understanding of the outer reaches of the Solar System and has played a role in the reclassification of Pluto as a dwarf planet. With its extreme distance from the Sun, highly elliptical orbit, and reflective surface, Eris provides valuable clues about the formation and evolution of Kuiper Belt objects.

1. 1. Size and Composition

• • • Diameter: Eris has an estimated diameter of about 2,326 km (1,445 miles), making it slightly smaller than Pluto but still one of the largest known dwarf planets.
    • Mass: Eris is roughly 27% more massive than Pluto. Its mass is about 1.66 x 10^22 kg.
    • Composition: Eris is composed mostly of rock and ice, with a surface that includes a significant amount of methane ice. Its composition suggests it has a mixture of rock and a thick icy crust.

 

1. 2. Orbit

• • • Orbit around the Sun: Eris orbits the Sun in a highly elliptical path, taking about 561 Earth years to complete one orbit. Its orbit is tilted, and eccentric compared to the planets, which means it has a highly variable distance from the Sun.
    • Distance from the Sun: Eris’s distance from the Sun varies greatly from about 38 AU (astronomical units) at perihelion (closest approach) to about 97 AU at aphelion (farthest distance). One AU is the average distance from Earth to the Sun.

 

1. 3. Surface and Atmosphere

• • • Surface features: Eris has a highly reflective surface due to the presence of methane ice, which reflects much of the sunlight that reaches it. This makes it one of the most reflective objects in the Solar System.
    • Atmosphere: Eris has a thin atmosphere that is primarily composed of nitrogen, with traces of methane. The atmosphere is thought to be extremely tenuous and freezes out onto the surface when Eris is farthest from the Sun.

 

1. 4. Temperature

Eris is incredibly cold, with surface temperatures estimated to be around -243°C (-405°F). The low temperatures are a result of its great distance from the Sun and its low solar energy absorption.

 

1. 5. Moon

Eris has one known moon, Dysnomia, which was discovered in 2005, the same year as Eris. Dysnomia is much smaller than Eris, with a diameter of about 700 km (430 miles). It orbits Eris at approximately 37,000 km (23,000 miles), completing an orbit roughly every 16 days.

 

1. 6. Interior

Eris likely has a rocky core surrounded by a thick icy mantle. Given its density, it’s inferred that it contains a significant amount of rock in addition to its icy surface.

 

1. 7. Discovery and Classification

• • • Discovery: Eris was discovered on January 5, 2005, by a team led by Mike Brown at the Palomar Observatory. The discovery of Eris was instrumental in the debate over Pluto’s planetary status, leading to the redefinition of the term “planet” by the International Astronomical Union (IAU) in 2006.
    • Dwarf Planet Status: Eris was classified as a dwarf planet due to its size, shape, and orbit. Like Pluto, Eris meets two of the three criteria for being a planet but does not clear its orbit of other debris.

 

1. 8. Orbital Characteristics

• • • Eccentric Orbit: Eris’s orbit is highly elliptical, meaning its distance from the Sun varies widely. This results in significant changes in its surface temperature and atmospheric conditions over time.
    • Inclination: Eris’s orbit is also highly inclined compared to the plane of the Solar System, which adds to its unique orbital characteristics.

 

1. 9. Scientific Significance

Eris has been an important object of study for understanding the outer Solar System and the nature of icy dwarf planets. Its discovery has provided insights into the composition, structure, and dynamics of distant Solar System objects.

 

1. 10. Interesting Facts

• • • Eris’s name: The dwarf planet is named after Eris, the Greek goddess of strife and discord. The name reflects the controversy and debate that surrounded the reclassification of Pluto as a dwarf planet.
    • Surface Brightness: Eris is one of the most reflective objects in the Solar System, with a surface brightness that reflects about 96% of the sunlight that hits it, primarily due to its methane ice.