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| Planet Definitions |
 Title text: Under the 'has cleared its orbital neighborhood' and 'fuses hydrogen into helium' definitions, thanks to human activities Earth technically no longer qualifies as a planet but DOES count as a star. |
Explanation
This comic addresses the controversy of whether of Pluto is a planet and explores many definitions, most of them humorous and nonsensical, of what a planet could be.
- Traditionalist
- Pluto is a planet (9 planets)
- In modern times, there was no formal definition of a "planet" prior to 2006. However, it was generally accepted as a colloquialism that there were nine planets around the Sun, Pluto included, primarily starting with Pluto's discovery in 1930, based upon that time's scientific consensus that there ought to be another planet to account for peculiarities in the the orbits of the other outer planets. As more sophisticated methods of mapping the Solar System were developed and Eris was discovered to be even more massive than Pluto (which may not have been as significant as the theories that led to its discovery suggested) it became clear to astronomers that a more standardized definition was needed. In 2006 the International Astronomical Union (IAU) published their formal redefinition of a "planet" to require a planet to be gravitationally dominant within its orbit, disqualifying Pluto (and Eris) which is now considered a "dwarf planet". This has been subject to push back from countless people, including some planetary scientists, but in mostly nostalgic laypeople dissatisfied with Pluto being "demoted" or otherwise relegated when schoolchildren and adults alike have 'known' that there are nine planets for the most part of the last century (and tradition has previously been referred to as whatever was current during "Baby Boomers' childhoods").
- Ironically, some of the latest study of the outer solar-system includes the possibility of yet another Planet Nine, but only time will tell if such an object exists and whether it would cross the IAU's current threshold or even require the threshold itself to be reassessed once more.
- Modern
- Pluto is not a planet (8 planets)
- When the IAU redefined what a planet is in 2006, Pluto no longer qualified as a planet (since it wasn't able to clear its neighborhood around its orbit). Using the modern, and recently official, definition of a planet, only eight celestial objects qualified: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- Expansive
- Dwarf planets are planets (17+ planets)
- It is likely that since the term "dwarf planet" contained "planet" in its name, Randall considered those as also planets under this category.
- It is also likely that the number of planets includes the ones that are considered planets and the ones that are considered to have compacted into fully solid bodies, as defined by Grundy et al., those being Ceres, Pluto, Eris, Makemake, Haumea, Gonggong, Quaoar, Orcus and Sedna.
- The basis for this viewpoint is the possible alternative re-evaluation that the IAU could have adopted, in that all newly discovered things like Pluto (being considered a planet) should therefore be considered a planet. Indeed, Ceres had been observed some time before Pluto and had been called a planet (or a "minor planet") within both scientific and public realms.
- Ultratraditionalist
- Only the classical planets are planets (5 planets)
- The classical planets are objects found and considered by the Greek astronomers in classical antiquity to be considered planets. Their definition of "planet" considered visible objects that move across the sky relative to the fixed stars, the original word itself being translated as "wanderer". There are seven classical planets, but if one were to only consider the ones that fall under the IAU's definition of a planet (this being less traditional), then there would only be five. (The Sun and the Moon would be disqualified.)
- Being (mostly) true to the spirit of the historic naming convention, this would be a conservative but 'valid' version of the criterion. Notably, Earth itself is not considered a planet by these criteria, as (from the prospective of anyone who might even consider such things), it was not even wandering the heavens, or in the night skies at all, but always underfoot.
- Condescending
- Only giant planets are planets; the rest are big asteroids (4 planets)
- This definition may refer to the giant planets, planets much larger than the Earth. Only the four outer (IAU-defined) planets fall under this definition.
- Relegation of anything smaller, including our own planet, is an extreme attitude, but most of the initial exoplanets discovered were, by practical necessity in their detection, also only of the "giant planet" kind.
- Simplistic
- Anything gravitationally round is a planet (37+ planets)
- Using the Wikipedia list of gravitationally rounded objects of the Solar System, there are 37 objects listed. That includes the Sun, 8 planets, 9 dwarf planets and 19 moons, but falls short of also highlighting all of the smallest visible objects (as per Universalist, below).
- This definition is essentially part of the actual current definition of a planet, leaving out the main factor that specifically disqualifies Pluto.
- Grounded
- Only objects a spaceship has landed on are planets (10 planets)
- This list includes objects in the Solar System that a spacecraft has performed a soft landing on. The list includes Venus, Earth, Mars, the Moon, Titan, Eros, Itokawa, Ryugu, Bennu and Churyumov-Gerasimenko.
- The justification for this seems to be that we must 'touch' the object before we consider it as worthy of being classified as more than a mere blob (or dot) in space.
- Regolithic
- Anything covered in dirt and ice and stuff is a planet (infinite)
- This list excludes the Gas Giants and the Ice Giants. The list would likely include dwarf planets, asteroids, moons and comets. This is effectively the opposite of the "condescending" definition: every object in the solar system is included in one definition or the other (except for the Sun).
- This is also an extension on the prior classification. In this case we could meaningfully touch the object, with predominantly atmospheric bodies being not considered so.
- Lunar
- You can't be a planet if you don't have a moon (12+ objects)
- Only some objects in the solar system have known and acknowledged moons orbiting them. The value given may be the number of planets and dwarf planets that have moons, when excluding Haumea for not reaching hydrostatic equilibrium despite having moons. The Sun is excluded because its satellites are not moons, because ... oh, look, a Squirrel!
- Adopting this definition would suggest that a planetary body is not worthy of the name if it doesn't (with no matter for what reason) demonstrably have the means to dominate its local area by being the overwhelming focus of all adjacent bodies' own orbits.
- Solipsistic
- Earth is the only planet (1 planet)
- Solipsism is the idea that only one's own mind is sure to exist. Randall extrapolated this idea to mean that only one's own planet that they are standing on is sure to exist.
- This projects (and relies upon) a more philosophical and/or semiotic assessment than any scientific one.
- Judgemental
- Only the prettiest ones are planets (6 planets)
- This list is likely formulated from Randall's own perception of the prettiest planets in the Solar System. Strangely, seven objects are highlighted:
- Earth
- Jupiter
- One of Jupiter's moons (unclear)
- Saturn
- One of Saturn's moons (unclear, possibly Titan)
- Neptune's moon (probably Triton)
- Pluto
- The subjectivity of this version of the definition makes it unlikely that a consensus of this form could be established.
- Empiricist
- Only worlds that I, author of this table, have personally seen are planets (12 planets)
- This list may refer to the celestial objects in the Solar System that have been made visible at night, probably using an optical telescope (a hobbyist one, perhaps Randall's, or from time borrowed on a major institutional installation). Jupiter's four largest moons are technically visible to the naked eye but hard to distinguish due to Jupiter's brightness, while Neptune is considered too faint to see (even if you know where to look). It may also be the case that Randall has never taken the time to look for Neptune while using a telescope. Apparently Randall has seen Uranus, which technically is visible to the naked eye under the very best viewing conditions, but these conditions are rare and it again requires knowing exactly where to look.
- The omission of the Sun from the list of worlds that Randall has personally seen is interesting. Yes, people are not supposed to stare at the Sun[citation needed], but it is not too uncommon to accidentally look in its direction for a split-second before instinctively closing one's eyes and turning one's head away.
- As a different form of subjectivity, the value of this grouping's criteria is questionable, but not uncommon in other 'softer' sciences.
- Marine biologist
- Only objects with oceans are planets (6+ planets)
- This list includes Earth, Europa, Ganymede, Callisto, Titan, and Enceladus. Most of these have had the presence of significant water identified from the way local magnetic/electric fields are detected, but see the following item.
- There is a resemblance, here, to a loose understanding of what a "world" is, i.e. one that possesses various distinct 'terrains' beyond mere dry (and possibly considered featureless) rock. A marine biologist would, of course consider a marine (if not pelagic or bathyspheric) environment to be an essential element of any world.
- Maritime
- Only objects with surface oceans are planets (2 planets)
- In the comic, only Earth and a Saturnian moon (likely to be Titan) are highlighted. Earth is the only body known in the solar system to have liquid water on the surface significant enough to be called an ocean. Titan's cold and dense atmosphere notably maintains surface 'seas' of methane and nitrogen, where other moons (given as additional in the prior item) seem to have their liquid water beneath either whole-surface ice caps or otherwise deep under the surface.
- From the narrower point of view of a sailor, for example, there is no benefit in considering water hidden away far beneath the surface, and it might as well not be there. Whereas it's possible that a well-prepared mariner could eventually sail the strange seas of Titan, as easily (or easier) as an airman might fly through its skies.
- Universalist
- They're all planets (infinite)
- This list claims that all objects are planets, all drawn items (also presumably all undrawn/undrawable items) being marked as such, including the Sun.
- Giving up on any thought of exclusivity, this unconventional view willingly inducts all visible objects into consideration.
- Existentialist
- What if space itself is a planet??? (Duude)
- This list is different from the list above as it claims that all of space, rather than only the objects existing in space, are planets. The interjection Duude expresses one's amazement at this 'revelation' and replaces the number count— and is sometimes stereotyped to imply the speaker is high on marijuana or other drugs popular with the 1960s hippie counterculture.
- The strange stretch of imagination, as prompted by some narcotic or other, abandons all pretense at sensibly sorting everything into "planet" or "not planet", as not only is everything a planet, but so is the nothing between these titular planets.
- Spiteful
- Only Pluto is a planet (1 planet)
- This list is a malicious play on the demotion of Pluto by demoting all other planets except Pluto instead, leaving Pluto as the only planet in the solar system.
- This is the taxonomic equivalent of refusing to play and taking your ball home to spite those who you think don't deserve it.
- (title text) Star
- Earth is a star (2 stars)
- In May 1934, Mark Oliphant, Paul Harteck and Ernest Rutherford at the Cavendish Laboratory, published an intentional deuterium fusion experiment, and made the discovery of both tritium and helium-3. This is widely considered the first experimental demonstration of fusion. Randall considers that this makes Earth fall into the category of a star due to the human-induced ability for Earth to fuse hydrogen into helium using nuclear fusion.
- One definition of a planet requires that the planet has cleared its "orbital neighborhood" of other objects - objects must either be captured as a moon, or have their orbits disrupted such that they are flung away. Under this definition, one could humorously argue that recent human activities, releasing new objects into orbit like the James Webb Space Telescope, technically disqualify Earth from being a planet, as the orbital neighborhood is no longer completely clear.
- By changing not only the definition, but the term being defined, this drifts yet further from any consensus view on the original question and into a typical punchline absurdity.
Transcript
- [A table with 3 columns, and 17 rows below the the header row, labelled "Definition", "# of planets" and "Solar system".]
- [In each row, the first column has a single word, in bold, then a descriptive sentence. The second column has a digit or other 'value'. The third column is a not-to-scale drawing of the Solar system, featuring the Sun, various 'planetary' bodies and an apparently selective sample of moons and asteroids, as follows: The Sun, Mercury, Venus, Earth with the Moon, Mars with its two moons (Phobos and Deimos), a small selection of some asteroid belt bodies (Ceres in the midst of other, smaller, examples), Jupiter and four of its moons (likely the Galilean moons: Io, Europa, Ganymede and Callisto), a ringed Saturn and usually one of its moons (probably Titan) or two (possibly Enceladus or Iapetus, as required), Uranus and four or five of its moons (likely to be Miranda, Ariel, Umbriel, Titania and Oberon, but one of these (shown upon the face of Uranus) only appears in some iterations of the base image), Neptune and one of its moons (probably Triton), Pluto and one of its moons (Charon), four more plutoid or Kuiper Belt objects (too little context to identify, but possibly Haumea, Makemake, Gonggong and Eris, in distance order), the first two of them with distinct moons indicated (entirely dependent upon which main objects they are).]
- [Each row's illustrated solar system has individual combinations of green highlights applied to the otherwise repeated diagram.]
- [Row 1: Definition:] Traditionalist: Pluto is a planet [Number:] 9 [Highlighted: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto]
- [Row 2: Definition:] Modern: Pluto is not a planet [Number:] 8 [Highlighted: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune]
- [Row 3: Definition:] Expansive: Dwarf planets are planets [Number:] 17+ [Highlighted: Mercury, Venus, Earth, Mars, Ceres (in Asteroid Belt), Jupiter, Saturn, Uranus, Neptune, Pluto and the further main bodies]
- [Row 4: Definition:] Ultratraditionalist: Only the classical planets are planets [Number:] 5 [Highlighted: Mercury, Venus, Mars, Jupiter, Saturn]
- [Row 5: Definition:] Condescending: Only giant planets are planets; the rest are big asteroids. [Number:] 4 [Highlighted: Jupiter, Saturn, Uranus, Neptune]
- [Row 6: Definition:] Simplistic: Anything gravitationally round is a planet [Number:] 37+ [Highlighted: The Sun, Mercury, Venus, Earth, The Moon, Mars, Ceres (without other asteroids), Jupiter + moons, Saturn with Titan, Uranus and its moons, Neptune with its moon, Pluto and the four further dwarf planets]
- [Row 7: Definition:] Grounded: Only objects a spaceship has landed on are planets [Number:] 10 [Highlighted: Venus, Earth, The Moon, Mars, five (non-Cererian) asteroids and Titan]
- [Row 8: Definition:] Regolithic: Anything covered in dirt and ice and stuff is a planet [Number:] [infinity symbol] [Highlighted: Mercury, Venus, Earth, The Moon, Mars, Ceres with all other asteroids depicted in the Asteroid Belt, the moons of Jupiter, the sole moon! of Saturn, the moons of Uranus, the moon of Neptune, Pluto with Charon, and all remaining dwarf planets with their moons]
- [Row 9: Definition:] Lunar: You can't be a planet if you don't have a moon [Number:] 12+ [Highlighted: Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and three of the other dwarf planets in the Kuiper belt, including one with no obviously drawn moon]
- [Row 10: Definition:] Solipsistic: Earth is the only planet [Number:] 1 [Highlighted: The Earth]
- [Row 11: Definition:] Judgemental: Only the prettiest ones are planets [Number:] 6 [Highlighted: The Earth, Jupiter with one of its moons (not identified), Saturn, one of two Saturnian moons in this image and Pluto]
- [Row 12: Definition:] Empiricist: Only worlds that I, author of this table, have personally seen are planets [Number:] 12 [Highlighted: Mercury, Venus, The Earth, The Moon, Mars, Jupiter with its four moons, Saturn and Uranus]
- [Row 13: Definition:] Marine biologist: Only objects with oceans are planets [Number:] 6+ [Highlighted: The Earth, three Jovian moons, the two illustrated Saturnian moons]
- [Row 14: Definition:] Maritime: Only objects with [next word in italics] surface oceans are planets [Number:] 2 [Highlighted: The Earth and Titan]
- [Row 15: Definition:] Universalist: They're all planets [Number:] [infinity symbol] [Highlighted: All drawn objects, including The Sun and all other objects including all the moons/asteroids]
- [Row 16: Definition:] Existentialist: What if space [next word in italics] itself is a planet??? [Word:] Duude [Highlighted: The whole third column cell]
- [Row 17: Definition:] Spiteful: [next word in italics] Only Pluto is a planet [Number:] 1 [Highlighted: Pluto]
Trivia
- In the original version of the comic, there were two errors that would later be fixed. The "Traditionalist" definition highlighted Neptune's satellite Triton instead of Pluto. The images of the Solar System for the "Traditionalist" and "Modern" definitions were swapped, resulting in Pluto being incorrectly highlighted in "Modern" and omitted in "Traditionalist.
- The "Judgemental" definition has seven colored objects instead of the labelled six. This mistake has never been fixed.
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