Trans-Neptunian Object (TNO)

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GCSE Astronomy (Lawrence Smallman, YouTube Playlist)


Trans-Neptunian Object (TNO) is any minor planet in the Solar System that orbits the Sun at a greater average distance (semi-major axis) than Neptune, 30 astronomical units (AU). Twelve minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known, which are called extreme trans-Neptunian objects (ETNOs).

The first trans-Neptunian object to be discovered was Pluto in 1930. It took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly, 15760 Albion. As of February 2017 over 2,300 trans-Neptunian objects appear on the Minor Planet Center’s List of Transneptunian Objects. Of these TNOs, 2,000 have a perihelion farther out than Neptune (30.1 AU). The most massive known trans-Neptunian object is Eris, followed by Pluto, 2007 OR10, Makemake and Haumea. The Kuiper belt, scattered disk, and Oort cloud are three conventional divisions of this volume of space, though treatments vary and a few objects such as Sedna do not fit easily into any division. — Wikipedia




Voyager Program is an American scientific program that employs two robotic interstellar probes, Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to fly near them while collecting data for transmission back to Earth. After launch the decision was taken to send Voyager 2 near Uranus and Neptune to collect data for transmission back to Earth. As of 2022, the Voyagers are still in operation past the outer boundary of the heliosphere in interstellar space. They collect and transmit useful data to Earth. — Wikipedia

Persistent Plasma Waves in Interstellar Space Detected by Voyager 1 (Stella Koch Ocker, et al., Nature Astronomy)
Voyager Mission (JPL, NASA)

Interstellar Boundary Explorer (IBEX or Explorer 91 or SMEX-10) is a NASA satellite in Earth orbit that uses energetic neutral atoms (ENAs) to image the interaction region between the Solar System and interstellar space. The mission is part of NASA’s Small Explorer program and was launched with a Pegasus-XL launch vehicle on 19 October 2008. IBEX is in a Sun-oriented spin-stabilized orbit around the Earth. — Wikipedia

Interstellar Boundary Explorer Mission (IBEX, NASA)

200 Transneptunian Objects (Harvard-Smithsonian Center for Astrophysics)

Trans-Neptunian Object (Wolfram Alpha)




Mathematical Discovery of Planets (J J O’Connor and E F Robertson)
Planets beyond Neptune (Wikipedia)


Melvil Decimal System # 523.49 Trans-Neptunian Objects (Library Thing)
Library of Congress Subject Heading: Trans-Neptunian Objects (Library Thing)

Library of Congress # QB701 Trans-Neptunian Object (UPenn Online Books)

WorldCat, Library of Congress, UPenn Online Books, Open Library




Trans-Neptunian Object (Astronomy Magazine)
Trans-Neptunian Object (
Trans-Neptunian Object (NPR Archives)


Trans-Neptunian Object (ISBNdb)



Trans-Neptunian Object (


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Here are links to pages about closely related subjects.

Knowledge Realm


Law (Constant) Relativity
Force Gravity, Electromagnetism (Light, Color)
Matter (Microscope) Molecule, Atom (Periodic Table), Particle

Universe (Astronomical Instrument)
Galaxy Milky Way, Andromeda
Planetary System Star, Brown Dwarf, Planet, Moon

Our Neighborhood
Solar System Sun
Terrestrial Planet Mercury, Venus, Earth (Moon), Mars
Asteroid Belt Ceres, Vesta
Jovian Planet Jupiter, Saturn, Uranus, Neptune
Trans-Neptunian Object
Kuiper Belt Pluto, Haumea, Makemake
Scattered Disc Eris, Sedna, Planet X
Oort Cloud Etc. Scholz’s Star
Small Body Comet, Centaur, Asteroid


1.   The resources on this page are are organized by a classification scheme developed exclusively for Cosma.