8.5 Trans-Neptunian Objects, the Kuiper Belt, and the Oort Cloud

Trans-Neptunian Objects (TNO) are any solar system minor planet that orbits the sun at a greater average distance than Neptune. Pluto is now considered a TNO, as is Eris. As of July 2014, over 1,500 trans-Neptunian Objects have been cataloged and of these, some 200 have been designated as dwarf planets. From Earth, astronomers study TNO heat emissions, colours, and spectra.The Kuiper Belt is a region beyond the orbit of Neptune at 30 Astronomical Units (AU) to about 50 AU from the sun. It is sometimes called the Edgeworth–Kuiper Belt. The Kuiper Belt is much larger than the Asteroid Belt. It’s about twenty times as wide and twenty to two hundred times as massive. Kuiper Belt Objects, called KBOs , are composed of rock and metal, like the asteroids, but also frozen ices like ammonia, methane, and water. Trans-Neptunian Objects are Kuiper Belt Objects (KBOs), but KBOs are not TNOs because the distance range of KBOs from the sun is much farther out in the solar system. At least two moons – Saturn’s Phoebe and Neptune’s Triton – are believed to be captured KBOs. To date, over 1,000 KBOs have been discovered and around 100,000 KBOs are suspected to exist.

KBOs are fragments from the original solar system’s protoplanetary disc that did not combine to form the more-massive and larger bodies. Astronomers believe that belts of fragments like the solar system’s Kuiper Belt are present around other stellar systems being studied.

Beyond Neptune

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.
Figure 8.27. Comparison of the largest TNOs: Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Orcus, Salacia, and 2002 MS4. All but two of these TNOs (Sedna and 2002 MS4) are known to have at least one moon. The top four are IAU-accepted dwarf planets while the bottom six are dwarf-planet candidates that are accepted as dwarf planets by several astronomers.
Largest known Trans Neptunian Objects by Lexicon, CC BY-SA 3.0.

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.

Attribution

“100 Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud” and “101 The Oort Cloud and Kuiper Belt” from Introduction to Astronomy by Florida State College at Jacksonville and Dr. Mike Reynolds are licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Fanshawe College Astronomy Copyright © 2023 by Dr. Iftekhar Haque is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.