The Oort Cloud and Kuiper Belt

The Oort Cloud is a hypothesized spherical cloud of icy objects up to 50,000 AU from the sun. This spherical cloud is the primary source of long-period comets. No Oort Cloud objects have been found, to date. Any object within the Oort Cloud would be called an Oort Cloud Object, (OCO) . The Oort Cloud would represent the physical boundary of the solar system.

Image of the comparison of the eight brightest TNOs: Pluto, Eris, Makemake, Haumea, Sedna, 2007 OR10, Quaoar, and Orcus. All except one of these TNOs (Sedna) are known to have moon(s). 2007 OR10 and Quaoar are currently estimated to be larger than Sedna. 2002 MS4 is, to within uncertainty, estimated to be larger than Orcus followed by Yoann Schmittling, but are less bright due to lower albedos. Since Quaoar and Orcus have moons, it is known that Quaoar is much more massive than Orcus. The top 4 are IAU-accepted dwarf planets while the bottom 4 are dwarf-planet candidates that are accepted as dwarf planets by several astronomers.
CC BY-SA 3.0 | Image courtesy of NASA and Wikimedia Author: Lexicon.