astronomy

List of trans-Neptunian objects

List of trans-Neptunian objects is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand List of trans-Neptunian objects rather than just read about it. In short: This is a list of trans-Neptunian objects (TNOs), which are minor planets in the Solar System that orbit the Sun at a greater distance on average than Neptune, which means all of their orbits have a semi-major axis greater than 30.1 astronomical units (AU). The Kuiper belt, scattered disc, and Oort cloud are three conventional divisions of this volume of space.

Key takeaways

List of trans-Neptunian objects belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect List of trans-Neptunian objects to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of List of trans-Neptunian objects from memory before moving on to harder problems.

Reference excerpt

This is a list of trans-Neptunian objects (TNOs), which are minor planets in the Solar System that orbit the Sun at a greater distance on average than Neptune, which means all of their orbits have a semi-major axis greater than 30.1 astronomical units (AU). The Kuiper belt, scattered disc, and Oort cloud are three conventional divisions of this volume of space. As of May 2026, the catalog of minor planets contains 1,049 numbered TNOs. In addition, there are 4,969 unnumbered TNOs, which have been observed since 1993. This list consists of all types of TNO subgroups: classical Kuiper belt objects, also known as "cubewanos", the resonant trans-Neptunian objects with their main and higher-order resonant subgroups, the scattered disc objects (SDOs), and the extreme trans-Neptunian objects including the ESDOs, EDDOs, and sednoids, which have a semi-major axis of at least 150 AU and a perihelion (closest approach to the Sun) greater than that of Neptune. The list also contains several centaurs, if the object's orbit has a sufficiently large semi-major axis (a). Centaurs have unstable orbits in which the perihelion (q) is well inside of Neptune's orbit but the farthest point (aphelion, Q) is very distant. The first TNO to be discovered was Pluto in 1930. It became the namesake of a larger group of resonant objects called plutinos (another such resonant subgroup are the twotinos). It took more than 60 years to discover a second TNO, Albion (provisionally known as 1992 QB1), in 1992. The largest known trans-Neptunian objects are Pluto and Eris, followed by Haumea, Makemake, Gonggong, Quaoar, Sedna, and Orcus, all of them being officially recognized as dwarf planets by the IAU except for Gonggong, Sedna, and Orcus. There are also many possible dwarf planets, such as Salacia, Máni, Varda, Ixion, and Varuna. Most TNOs have low albedos typically around 0.09. Their color varies from blue-grey to very red (classes BB, BR, IR and RR). The following list also gives an object's full designation, mean-diameter (D), and discovery circumstances (date, discoverer and discovery site), as well as its orbital inclination (i) and eccentricity (e).

List

This list includes all numbered trans-Neptunian objects with a semi-major axis greater than 30.1 astronomical units (AU), Neptune's average orbital distance from the Sun. The data is sourced from MPC's "List of Trans Neptunian Objects", "List Of Centaurs and Scattered-Disk Objects", "List of Neptune Trojans", "List Of Other Unusual Objects", and "Database Search", completed with remarks and information from Johnston's Archive (diameter, class, binary, albedo, spectral taxonomy and B–R color index).

Unnumbered TNOs

There are 4,969 unnumbered trans-Neptunian objects, defined here as minor planets with a semi-major axis larger than 30.1 AU (Neptune's average orbital distance from the Sun). The data is sourced from MPC's "List of Trans Neptunian Objects", "List Of Centaurs and Scattered-Disk Objects", "List Of Other Unusual Objects", and "Database Search", completed with information from Johnston's Archive (diameter, class, binary status, etc.). For the list of numbered TNOs, see § List.

Trans-Neptunian satellites

A growing number of TNOs are revealed to be binary systems with a minor-planet moon orbiting its primary. There are also several multiple systems with more than one satellite.

Diagram: orbital classes

Trans-Neptunian objects colorized by their orbital subclass and plotted in the orbital parameter space (eccentricity and inclination versus semi-major axis). The plot for the entire region contains 1418 objects including plutinos (#185), twotinos (#36), other resonant objects (#124), cubewanos (#420), inner (#40) and outer classical objects (#6), SDOs (#289), sednoids (#11), centaurs (#101) and other TNOs (#206).

See also Lists of astronomical objects List of centaurs (small Solar System bodies) List of minor planets List of the brightest Kuiper belt objects List of Solar System objects by greatest aphelion List of Solar System objects most distant from the Sun Planet Nine

Notes

References

External links How many dwarf planets are there in the outer solar system?, Michael Brown, Caltech OSSOS TNODB by the Outer Solar System Origins Survey Minor Planet Center: List of Transneptunian Objects Minor Planet Center: List of Centaurs and Scattered-Disk Objects Johnston's Archive: List of Known trans-Neptunian Objects Johnston's Archive: Trans-Neptunian Objects Known extreme outer solar system objects, Scott Sheppard, Carnegie Science Center Minor Planet Center Database Search: Objects with a semi-major axis at least 30.1 AU

Illustrations

Worked examples

Example 1 — a first encounter with List of trans-Neptunian objects

Start with the simplest possible case. Write down what List of trans-Neptunian objects claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to List of trans-Neptunian objects before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about List of trans-Neptunian objects ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of List of trans-Neptunian objects

In research: List of trans-Neptunian objects appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses List of trans-Neptunian objects in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: List of trans-Neptunian objects is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lists of small Solar System bodies, Lists of trans-Neptunian objects, Trans-Neptunian objects, so understanding it makes those chapters shorter.
In everyday life: Look for List of trans-Neptunian objects outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study List of trans-Neptunian objects in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what List of trans-Neptunian objects means in your own words.
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Work through the three examples above with pen and paper.
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Frequently asked questions

What is List of trans-Neptunian objects in simple terms?

Why does List of trans-Neptunian objects matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study List of trans-Neptunian objects?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on List of trans-Neptunian objects.