Almost two years ago, during the same contentious meeting in which Pluto was demoted from a full-fledged planet to a “dwarf planet,” a few other votes were taken, but mostly forgotten. One of the forgotten votes that was actually approved was that Pluto was to be declared the” prototype of a new class of objects”. OK. Done. What exactly that means is a bit hard to say. As far as I could tell it was an attempt to be nice to Pluto after the indignity of its demotion. Who would vote “no” to that?
The next vote that was taken was about what to call this new class of objects. The proposal, if I remember correctly, was to call them “Plutonian objects.” The proposal was voted down by a very small margin. Why, again? Hard to say. People were in funny moods.
The class of objects, then, remained unnamed, with a promise – a threat – that a committee would come up with something and there would then be no vote.
The committee has spoken! After the close vote on “Plutonian objects”, the committee deliberated for almost two years and settled on “Plutoids” and now it is settled. A “Plutoid” is a dwarf planet (meaning it must be large enough to be round) that is beyond Neptune.
But wait! There’s more! The committee did more than promised! They added one more twist to the rule. While originally all dwarf planets beyond Neptune were to be part of this new category, the committee decided to restrict the definition to the brightest of the dwarf planets. For now the only ones that count are Pluto itself, as well as three of my babies: Eris, 2005 FY9, and 2003 EL61.
I have been asked: will there be controversy? Will there be bickering? Will people fight and contend?
I suspect the answer is, in fact, that there will mostly be nothing.
The class of objects was supposed to get a name, now it has a name. The name seems pretty non-controversial, if also a bit clunky.
The one thing that almost no one will even notice is the part that I find the most odd, though, which is the restriction that the object be a particular brightness. Not a particular size: a particular brightness.
That makes for some funny situations. If you take Pluto and cover it with dirt it would no longer be a Plutoid. Or take something much smaller and cover it was snow instead of rocks and it might be a Plutoid. Or, may favorite example, if you take Eris, which is currently the intrinsically brightest object, bring it closer to the sun (where it will be in 290 years), melt some of the ice on the surface, and exposure some of the darker substrate, it might just get dark enough to no longer be a Plutoid. Now you see it; now you don’t.
But, OK, it’s a definition. And I can at least understand the committee’s feeling that they wanted to put a concrete brightness limit instead of a harder to determine roundness limit.
What does anyone else think?
There is still a small but extremely vocal group of astronomers who remain incensed about Pluto’s demotion. They will use this as a soapbox to repeat their initial complaints about Pluto.
Other astronomers are likely to yawn. Plutoids? Sure, why not. Most astronomers have moved well beyond the Pluto-debate and the semantics associated with it. If Pluto is happy being a Plutoid then it is probably OK with the rest of us.