Trans-Neptunian object

Artistic comparison of Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Orcus, Salacia, 2002 MS4, and Earth along with the Moon

Illustration of the relative sizes, albedos and colours of some large TNOs

A trans-Neptunian object (TNO), also written trans Neptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au).

Typically, TNOs are further divided into the classical and resonant objects of the Kuiper belt, the scattered disc and detached objects with the sednoids being the most distant ones. As of October 2020, the catalog of minor planets contains 678 numbered and more than 2,000 unnumbered TNOs.

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. The most massive TNO known is Eris, followed by Pluto, Haumea, Makemake, and Gonggong. More than 80 satellites have been discovered in orbit of trans-Neptunian objects. TNOs vary in color and are either grey-blue (BB) or very red (RR). They are thought to be composed of mixtures of rock, amorphous carbon and volatile ices such as water and methane, coated with tholins and other organic compounds.

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).

List of notable TNOs

• Pluto, Eris, Haumea and Makemake. The 4 TNOs that are dwarf planets based on the IAU opinion.
• Orcus, Quaoar, Gonggong and Sedna. 4 TNOs that are considered by most astronomers to be dwarf planets.
• Salacia, 2002 MS4, 2002 AW197, Varda, 2013 FY27 and Ixion. Notable TNOs due to their large size.
• 15760 Albion, the first TNO discovered after Pluto.
• Lempo, a trinary system consisting of a central binary pair of similar size, and a third outer circumbinary satellite.
• Arrokoth, a contact binary cubewano encountered by the New Horizons spacecraft in 2019.
• 2018 VG18 "Farout", the first trans-Neptunian object discovered while beyond 100 au (15 billion km) from the Sun.
• 2018 AG37 "FarFarOut", most distant observable trans-Neptunian object at 132 au (19.7 billion km) from the Sun.
• Varuna, a large cubewano, also known for its rapid rotation (6.3 h) and elongated shape
• Gǃkúnǁʼhòmdímà, for its unusual name.

Gallery

Pluto the only dwarf planet visited by a space probe along with Ceres. Also the most massive known TNO

Arrokoth the only TNO (along with Pluto) to be visited by a space probe

Eris is the most massive and second largest known dwarf planet and TNO

Haumea one the only 2 TNO (along with Quaoar) to have rings

Sedna the dwarf planet with most eccentric orbit

2018 AG37 "FarFarOut", the further TNO discovered as of now