Trans-neptunian Object (tno)

Any object with a mean orbital diameter larger than that of Neptune. Pluto and its moon Charon are both TNOs, as are all the objects in the Kuiper BeltRegion in the outer solar system beyond Neptune's orbit that contains billions of small, icy planetesimals from the original protoplanetary disc that failed to coalesce into planets. The Kuiper Belt extends from Neptune's orbit at 30 AU to ~55 AU. It is ~20x wider and 20-200x more massive than the and the Oort CloudVast spherical swarm ~1012-1013 long-period comets orbiting the Solar System with semimajor axes between 1,000 and 50,000 AU, typically with low orbital eccentricity. The Oort cloud, while roughly spherical at the largest radius, is wedge-shaped where it merges with the outer planet region in the vicinity of the Kuiper belt. A list of the known TNOs is given at: http://www.cfa.harvard.edu/iau/lists/TNOs.html.