Trans-Neptunian Objects

A trans-Neptunian object (TNO) is any object in the solar system that orbits the Sun at a greater average distance than Neptune, hence including objects in the Oort Cloud (more later) as well as the Kuiper belt. Sedna is a large trans-Neptunian object, which in 2012 was about three times as far from the Sun as Neptune. Like other TNOs its surface is largely a mixture of water, methane and nitrogen ices, though it is also one of the reddest in the solar system. It is probably a dwarf planet. Sedna’s exceptionally long and elongated orbit, taking approximately 11,400 years to complete, and distant point of closest approach to the Sun, at 76 AU, have led some astronomers to conclude that it is the first known member of the inner Oort cloud