90377 Sedna - Classification

Classification

The Minor Planet Center, which officially catalogs the objects in the Solar System, classifies Sedna as a scattered object. However, this grouping is heavily questioned, and many astronomers have suggested that it, together with a few other objects (e.g. 2000 CR₁₀₅), be placed in a new category of distant objects named extended scattered disc objects (E-SDO), detached objects, distant detached objects (DDO) or scattered-extended in the formal classification by the Deep Ecliptic Survey.

The discovery of Sedna resurrected the question of which astronomical objects should be considered planets and which should not. On March 15, 2004, articles on Sedna in the popular press reported that a tenth planet had been discovered. This question was answered under the International Astronomical Union definition of a planet, adopted on August 24, 2006, which mandated that a planet must have cleared the neighborhood around its orbit. Sedna has a Stern–Levison parameter estimated to be much less than 1, and therefore cannot be considered to have cleared the neighborhood, even though no other objects have yet been discovered in its vicinity. To qualify as a dwarf planet, Sedna must be shown to be in hydrostatic equilibrium. It is bright enough, and therefore large enough, that this is expected to be the case.