Sednoid

A sednoid is a trans-Neptunian object with a perihelion well beyond the Kuiper cliff at 47.8 AU. Only four objects are known from this population: 90377 Sedna, 2012 VP113, 541132 Leleākūhonua (2015 TG₃₈₇), and 2021 RR205, but it is suspected that there are many more. All four have perihelia greater than 55 AU. These objects lie outside an apparently nearly empty gap in the Solar System and have no significant interaction with the planets. They are usually grouped with the detached objects. Some astronomers 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, beyond the aphelia of the four known sednoids.

One attempt at a precise definition of sednoids is any body with a perihelion greater than 50 AU and a semi-major axis greater than 150 AU. However, this definition applies to objects such as 2013 SY99, which has a perihelion at 50.02 AU and a semi-major axis of about 700 AU but it is thought to not belong to the Sednoids, but rather to the same dynamical class as 474640 Alicanto, 2014 SR349 and 2010 GB174.

With their high eccentricities (greater than 0.8), sednoids are distinguished from the high-perihelion objects with moderate eccentricities that are in a stable resonance with Neptune, namely 2015 KQ174, 2015 FJ345, (612911) 2004 XR190 ("Buffy"), 2014 FC72 and 2014 FZ71.