If I understand the argument correctly, the population based approach consists of matching like with like. And Pluto is indeed a Kuiper belt object: its orbit is off the solar plane and even crosses Neptune’s orbit at times.
But that’s an odd way to define a planet, unless you believe that planets only exist in our solar system. And that doesn’t appear to be common usage either among astronomers or the general public. I can imagine fixing a cutoff of size, mass, atmosphere, geologic characteristics or (as I prefer) shape to designate a planet. But location is fairly odd.
(Note “Dynamically dominate” is a little better than “Clear its neighborhood”, which technically Earth doesn’t even do in its own orbit, though it does a better job than Pluto by orders of magnitude. See upthread discussion.)
Another argument says that if we admit Pluto, we will have to admit hundreds of other objects. I think I showed in post 40 that this is not necessarily the case. That said and to repeat definitions are arbitrary and characteristics matter more than labels; this thread was intended as a decent entry point into planetary science for non-experts. I’ve learned a lot anyway. I presume that those familiar with the subject roll their eyes a little. My WAG is that roundness isn’t a criteria because it is difficult to measure relative to its scientific importance.
Meanwhile, scientists debate which trans-Neptune object they will send the New Horizons spacecraft towards: the decision is expected next month. All 3 potential targets are 20-55 kilometers across. If all goes well one of them would be visited in 2018-2019.
Then biological taxonomy is the thing for you! Once someone’s named a species, that’s IT, even if everything they thought about it was wrong (other than it being the first specimen of a previously unnamed species). This path leads to confusion, too.
I call Pluto “one of the historical 9 planets.” I think that gives it proper homage. But I also call it a dwarf planets. For some silly reason, I’d like to know the names of all the planets, and that list above just isn’t going to cut it! And seriously, there is a significant distinction between the 8 planets and the dwarf planets, and it doesn’t hurt to give that distinction a name.
But, it’s all semantics. We’re not arguing science, just nomenclature, so it really doesn’t matter.
Well …
So, as it turns out, those newsheads aren’t necessarily wrong after all, unless they’re talking about the mythical figure.
But I find that I was pronouncing them both wrong in my head all these years, thinking the stress was on the second syllable, and that the ‘o’ was long. Ignorance fought!
That’s far from the case. Species are reclassified into different genera all the time, which often causes a change in the specific (second) name because its Latin gender is different from the new genus. Also, the specific name may have to be changed entirely if it is preoccupied by another species in the new genus. And while mistakes made in the original naming of species are generally retained, inadvertent spelling errors can be corrected at a later date.
Every year, I have to update my species lists because of changes and revisions issued by the American Ornithologists’ Union. It drives me crazy.
Thanks for the correction. I was thinking of the “type specimen” system (where the first one found and preserved is named and all other examples are referenced to that – even if the first is in poor shape or missing a lot), but clearly even with that system things change.
Perhaps they should just give each species a UUID, and then it’d be easy to update name references. You’d still have to update things when one species turns out to be (judged to be) two, or vice-versa. Since there’s no objective criteria for what constitutes a species, I imagine this happens enough to be a nuisance.
In older literature, sometimes a describer failed to designate a single type specimen from among a group of specimens, which can be a problem with cryptic species in which specimens of two species may have both been included in the type description. A few years ago I had to designate what’s called a lectotype for a subspecies which was described on the basis of 14 specimens selecting a specific one.
Actually, a DNA bar-coding system is being developed for species, but this depends on sections of the genetic code rather than designating an UUID.
Hygiea … discovered in 1849, … is much more spherical than we originally thought.
In order to be a dwarf planet, an object must satisfy four criteria: it has to orbit the sun, it cannot be a moon, it must not have swept up all the smaller objects in its orbit, and it must have enough mass that its own gravity has pulled it into a spherical shape. We already knew that Hygiea satisfied the first three, and the new images taken by Miroslav Brož at Charles University in Prague and his colleagues show that it satisfies the fourth.
Has link to other discussions on “roundness,” definitions…
I thought another criteria for a planet wasclearing the neighborhood of its orbit.. That’s why Ceres isn’t a planet, it shares the neighborhood of its orbit with umpteen other asteroids.
What a planet is not is something decided by the IAU. If they want to invent new categories for celestial bodies they can come up with their own words.
My understanding is that Hygiea was thought to have partially melted because of that collision, which means it would have been in a rough hydrostatic equilibrium until it resolidified.
Anyway, it’s not a dwarf planet until so declared by the IAU. They came up with the category, so they own it. Note that they haven’t added any to the list since the original five, even though there are many likely candidates. My guess is that no one there is enthused about the category, so no action. It certainly isn’t a scientificly useful category.
Please be informed that members of family Columbidae, aka pigeons, have been reclassified as planets due to their general roundness and tendency to clear their local area of neighbors. Henceforth, the family name Planetidae shall be used.
–President, American Ornithologists Union
