- #1
Jupiter60
- 79
- 22
After all, dwarf stars are a subset of stars and dwarf galaxies are a subset of galaxies, shouldn't a dwarf planet be a type of a planet?
Dwarf main sequences stars are not a subset of main sequence stars, nor are dwarf galaxies a subset of galaxies. They are simply smaller stars, smaller galaxies, and smaller planets. Red dwarf (spectral type M) stars should not be confused with degenerate white dwarf stars. While they are both very small stars, one still fuses hydrogen (the red dwarf), whereas the other is a dead star (the white dwarf) and no longer fuses hydrogen.Jupiter60 said:After all, dwarf stars are a subset of stars and dwarf galaxies are a subset of galaxies, shouldn't a dwarf planet be a type of a planet?
ogg said:Why "should" they? Would that change in structure of the categorization lead to a change in their physical properties? Of course not. The utility of a categorization is to enable generalization (abstraction) and/or improve communication. Which purpose would that change address and how? Your question seems to me to be equivalent to asking whether the word "planet" should be capitalized. What possible difference would it make? Many (if not most) of their similarities with the planets are known, so there seems to be no good reason to invent a more general category which includes both planets and dwarf planets and nothing else. You may want to read more about the criticisms of the IAU definition of planet - Wikipedia article of that name discussed it, iirc.
Why? What difference does it make?Jupiter60 said:If dwarf planets are not planets, they should call them by some other name, not "dwarf planets".
This is a red herring argument. Interestingly, red herrings are almost always neither red nor herrings.Jupiter60 said:If dwarf planets are not planets, they should call them by some other name, not "dwarf planets".
Every science has its oxymoronic terms, including astronomy. For example, neutron star and Martian geology.Ken G said:I don't know of a single other case in all of astronomy where a "X Y" is not a type of Y, except for "dwarf planet."
Not amongst dynamicists. Your hopes are most likely as moot as were those of the discoverers of the first four asteroids, which were categorized as planets for the first half of the 19th century.I think it's quite a silly way to build a category and I hope they come to their senses soon. But it's rather moot, because most actual practitioners of planetary astronomy certainly do consider dwarf planets to be planets, indeed they consider moons to be planets also.
All the same, neither of those are counterexamples to my point.D H said:Every science has its oxymoronic terms, including astronomy. For example, neutron star and Martian geology.
So your logic is, if you can cite a subset of astronomers who care about the official meaning of "planet", and I can cite a subset who don't care at all what other people regard as "planets", that makes my point moot? I don't follow that logic. What I'm saying is, there is an entire subfield of astronomy called "planetary astronomy" which, in general, includes essentially zero interest in the IAU classification of "planet", but a whole lot of interest in the common physics, and contrasts, among objects that are of interest to "planetary astronomy." In that latter camp, a "dwarf planet" is very much a subclass of "planet", expressly because of the interesting physics they share with what the IAU might wish to call a "planet." For them, it makes no difference at all how many planets we count in the solar system, it is their physics that they care about.Not amongst dynamicists. Your hopes are most likely as moot as were those of the discoverers of the first four asteroids, which were categorized as planets for the first half of the 19th century.
Dwarf planets are not considered full-fledged planets because they do not meet all the criteria set by the International Astronomical Union (IAU) for a planet. According to the IAU, a planet must orbit around the sun, have enough mass to form a spherical shape, and have cleared its orbit of other objects. Dwarf planets, on the other hand, do not have enough mass to clear their orbit of other objects.
Dwarf planets are different from regular planets in terms of size, shape, and orbital characteristics. They are much smaller than regular planets and often have irregular shapes. Additionally, they do not have enough mass to clear their orbit of other objects, unlike regular planets.
While dwarf planets do orbit the sun, this is not the only criteria for being considered a planet. As mentioned earlier, the IAU has set specific criteria for a celestial body to be classified as a planet, and dwarf planets do not meet all of these criteria. Therefore, they cannot be considered a subset of planets.
The IAU changed the definition of a planet in 2006 to exclude dwarf planets because the discovery of new celestial bodies, such as Eris and Ceres, raised questions about how to classify them. The IAU wanted to create a clear and specific definition for a planet to avoid confusion and inconsistencies in classification.
It is unlikely that dwarf planets will be reclassified as regular planets in the future. The IAU definition of a planet is based on scientific research and consensus, and any changes to this definition would require significant evidence and agreement from the scientific community. However, the classification of celestial bodies is always evolving, so it is possible that new discoveries may lead to changes in the definition of a planet.