Nomenclature Nightmare: TNOs

Hi there, loyal readers! As school here in CUNY resumes itself, I find myself preparing for my classes, and going over some of my old notes (I do this because I like to use the same book for multiple classes, so I end up reading over some things). While doing this, I remembered something that has always bothered me; I hate bad scientific nomenclature. In general, people who aren’t scientists often find science to be very confusing and intimidating…and to be honest, I often get intimidated just by looking at the names. Have you ever attended a biology talk? I can never understand what they’re talking about unless they tell me in non-latin terms.

Notice that "Intimidation" is 5 syllables long.

I’m not just talking about Biology…that just wouldn’t be fair. It’s all over the place. Even in my own field of Astronomy, confusion abounds. One of the worst things is our naming system for various types of rocky bodies farther out than Neptune. I’m going to name a few of them…and yes, there will be a quiz at the end. So pay attention. Ok…no quiz…but seriously, pay attention.

As most people are aware, Pluto is no longer a planet (and for good reason: see older post for explanation), but objects like it are the victims of an overabundance of nomenclature. To illustrate what I mean, I’m going to tell you every category Pluto fits into. Are you ready?

These aren’t even all the categories. But let’s now examine these particular categories in more detail, because most likely, you don’t know what most of them are, and would easily confuse them if someone referenced them in conversation (because clearly the latest plutino discovery makes for fantastic discussion on your third date). I’m not going to talk about dwarf planets — for explanation see older post “Pluto is Not a Planet”.

To change things up, I’m going to work up the list. A “Kuiper Belt Object” is self-explanatory…it is an astronomical body (object) that resides in the Kuiper Belt, which, similar to the asteroid belt, is a doughnut shaped region past Neptune with many “small” objects. There is a similar region slightly farther out which scientists now like to call the “Scattered Disk”…this region contains Eris, the hated dwarf planet bigger than Pluto. Now of course, all Kuiper Belt objects and Scattered Disk objects are part of a grander category called “Trans-Neptunian Objects” (TNOs), which are objects orbiting the Sun that are farther out than Neptune.

Pluto happens to be a Resonant TNO, which means that it is in orbital resonance with Neptune. In easier terms, Pluto’s orbit is affected by Neptune in such a way that for every 3 orbits Neptune makes, Pluto makes 2. Hence, they are in 2:3 orbital resonance with each other. As you may imagine, there are other objects that share a 2:3 orbital resonance with Neptune…these objects are the ones known as “plutinos”. My favorite plutino is the dwarf planet named Orcus, which has almost the exact opposite orbit of Pluto, and so it is also known as the Anti-Pluto. TNOs can have other orbital resonances as well (e.g. 1:2 resonant bodies called “twotinos”, 1:1 resonant bodies called “Neptune Trojans”).

Now for the last one on the list…plutoids. To me, the category of “Plutoid” is completely unnecessary, and downright confusing. According to the International Astronomical Union (IAU), “Plutoids are celestial bodies in orbit around the Sun at a semimajor axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit. Satellites of plutoids are not plutoids themselves.” So basically, this means that Plutoids are the exact same as Dwarf Planets, the only difference is that they are farther than Neptune. That’s it. So take a list of all the dwarf planets, and cut out all those closer than Neptune. Isn’t that the most stupid idea we’ve had in a while? In addition to being of little use, it’s so similar to “Plutino” and “Pluto” that it is easily confused.

I’m sure there are plenty of arguments as to why it might be useful to make such overlapping categories as to find similar properties of objects. But a couple of them, like Plutoids, seem redundant, and if you are going to have so many similar categories, then at least use names that won’t be so easily confused with each other! Using Pluto as a name for two separate, similar categories just seems like poor nomenclature choice. I like to call this problem the “Nomenclature Nightmare.” And that’s not ambiguous.

There are many other nomenclature nightmares, but for the sake of time, I’ll save other examples for a different entry. If you guys have examples of the Nomenclature Nightmare, comment and tell us about it! It’s a big problem, and we need to make sure to make people aware of the issue, and at the very least, educate each other as to how to survive the system (changing the system isn’t likely once it’s established, we just have to deal with it). If you have trouble with TNOs, just remember this entry! And so, I will see you next time for more science!

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3 Responses to Nomenclature Nightmare: TNOs

  1. Kelle says:

    In this particular case, I think the nomenclature nightmare reflects a rapidly changing field of study and a lack of consensus rather than an attempt of anyone to make useful overlapping categories. I think that as the nature of the outer Solar System is better understood, the nomenclature will converge.

    In brown dwarf astronomy, people will call an object with a mass estimate of ~10 M_Jupiter, a “planetary-mass brown dwarf”, a “free-floating planet” if it’s not a binary system, or a “planet” if it’s connected to something more massive, even just another brown dwarf. Which nomenclature one uses depends on which “club” they belong to and is also varies by geography (US vs. Europe).

    And you’re exactly right. It’s a big struggle for young students to learn all of the jargon and it’s best to learn how to deal with it rather than spend any effort at all trying to change it. Just wait till you start to try to decipher the alphabet zoo of instruments, telescopes, and space missions!

  2. ojimori says:

    Thanx information
    The flagship Science Magazine web site provides the total text of the journal’s news stories, analysis reports, and commentary articles in a very searchable database, enhanced by extra data, links, multimedia, and user services, further as a database of scientific-product data.

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