What Are Trans-Neptunian Objects?

Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will discuss trans-Neptunian objects, the Kuiper belt, Kuiper belt objects, dwarf planets, and plutinos, as well as where they are found in our solar system.

The Asteroid Belt

Most of you are likely all too aware of the asteroid belt. The asteroid belt is a region in our solar system that's located between Mars and Jupiter and is filled with lots of asteroids, simple as that.

Asteroids are the most important small celestial objects of the inner solar system. However, they are not so dominant in the outer solar system. In this lesson, we'll go over what is dominant over there, what they're called, and which famous celestial body you're certainly aware of that's part of them.

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  • 0:02 The Asteroid Belt
  • 0:32 Trans-Neptunian Objects
  • 1:56 Kuiper Belt Objects & Plutinos
  • 3:41 Lesson Summary
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Trans-Neptunian Objects

The outer solar system is filled with trans-Neptunian objects (TNOs). These are small planetary bodies whose orbits are found beyond the orbit of Neptune. Since the prefix 'trans-' means 'beyond' in Latin, it's going to be kind of easy to remember that they are beyond the orbit of Neptune in our solar system.

The largest TNOs are called dwarf planets. A dwarf planet is a celestial body orbiting around the sun that isn't a satellite of a planet, and one that is massive enough to form a more-or-less spherical shape but not massive enough to clear away all or almost all other bodies in the vicinity of its orbit.

The most famous such dwarf planet is none other than Pluto. Of course, there are other dwarf planets, like Eris and Ceres.

Dwarf planet or not, over 1,000 trans-Neptunian objects have been found to date, and more are being discovered all of the time. Astronomers estimate there are many more. So many more that they believe the mass of all of the TNOs is several hundred times greater than the mass of all the asteroids in the inner solar system. Oh, and by the way, all of these objects orbit the sun in the same direction as the planets.

Kuiper Belt Objects and Plutinos

As the intro implied, asteroids are found in the asteroid belt. Well, most TNOs are found within a band called the Kuiper belt. The Kuiper belt is a region of space, filled with small, icy bodies, which is found stretching from 30 AU (just beyond the orbit of Neptune) to at least 100 AU from the sun. An object found in the Kuiper belt is appropriately called a Kuiper belt object (KBO).

The Kuiper belt objects are icy leftovers of the outer solar nebula. Such objects likely formed at about the same time as the planets in our solar system. However, as per the prior definitions, they never got big enough to sweep out their orbital areas of pesky planetesimals. Thus, instead of being free and clear of such celestial bodies, they remained trapped within a massive amount of other such objects in the Kuiper belt.

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