Sednoid

A sednoid is a trans-Neptunian object with a perihelion greater than 7012747989353500000♠50 AU and a semi-major axis greater than 7013224396806050000♠150 AU. Only two objects are known from this population, 90377 Sedna and 2012 VP113, both of which have perihelia greater than 7013112198403025000♠75 AU, but it is suspected that there are many more. These objects lie outside an apparently nearly empty gap in the Solar System starting at about 50 AU, and have no significant interaction with the planets. They are usually grouped with the detached objects. Some astronomers, such as Scott Sheppard, consider the sednoids to be inner Oort cloud objects (OCOs), though the inner Oort cloud, or Hills cloud, was originally predicted to lie beyond 2,000 AU, several times as far as the aphelia of the two known sednoids.

Unexplained orbits

The sednoids' orbits cannot be explained by perturbations from the giant planets, nor by interaction with the galactic tides. If they formed in their current locations, their orbits must originally have been circular; otherwise accretion (the coalescence of smaller bodies into larger ones) would not have been possible because the large relative velocities between planetesimals would have been too disruptive. Their present elliptical orbits can be explained by several hypotheses: