Sedna is a trans-Neptunian object (TNO) and a possible dwarf planet located in the outer reaches of the Solar System. It was discovered on 14 November 2003 by a team led by Mike Brown, Chad Trujillo, and David Rabinowitz using the Samuel Oschin Telescope at Palomar Observatory.
Discovery and designation
- Provisional designation: 2003 VB₁₂.
- Permanent minor‑planet number: 90377.
- Official name: Sedna, after the Inuit goddess of the sea.
Orbital characteristics (as of the J2000 epoch)
- Semi‑major axis: ~519 AU (average distance from the Sun).
- Perihelion (closest approach to the Sun): ~76 AU.
- Aphelion (farthest distance): ~937 AU.
- Orbital period: ≈ 11 500 Earth years.
- Eccentricity: ≈ 0.85, indicating a highly elongated orbit.
- Inclination to the ecliptic: ~11.9°.
Sedna’s orbit is detached from the Kuiper Belt and is not significantly influenced by the known giant planets, leading to hypotheses about past stellar encounters or the presence of unseen massive objects shaping its trajectory.
Physical characteristics
- Estimated diameter: ~1 000 km (range 900–1 050 km, based on thermal observations).
- Albedo (reflectivity): ~0.32, inferred from infrared measurements.
- Surface composition: Spectroscopic data indicate the presence of water ice, methane, and possibly nitrogen ices.
- Color: Very red, consistent with a surface coated by tholins produced by cosmic radiation.
Classification
The International Astronomical Union (IAU) has not formally designated Sedna as a dwarf planet, but its size and mass place it within the range of known dwarf planets such as Pluto and Eris. Consequently, many scientific sources refer to Sedna as a “dwarf planet candidate.”
Observational history
Sedna is extremely faint (apparent magnitude ~21) due to its great distance and small size, requiring large telescopes for detection and follow‑up observations. Its slow apparent motion across the sky necessitates long‑term monitoring to refine orbital parameters.
Scientific significance
Sedna’s distant, detached orbit provides insight into the dynamical history of the outer Solar System, contributing to models of planet formation, migration, and potential external perturbations (e.g., passing stars or a hypothesized distant massive planet). Its surface composition also offers clues about the chemical inventory of primordial Solar System material.
