3063: Planet Definitions

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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 explanation is incomplete: A table might be better to format the explanation. If you can fix this issue, edit the page!

This comic addresses the controversy of whether of Pluto is a planet and explores many definitions, most of them humorous/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 lead 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 refered 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 qualifies 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.

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.

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" mind.

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 and Bennu. Notably, comet landings are not included in the list.

The justification for this seeks 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 could we meaningfully touch the object, with predominatingly 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 assesment 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 pellagic 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 additonal 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.

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

This transcript is incomplete: Do NOT delete this tag too soon. If you can fix this issue, edit the page!

[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/asteroids, as follows: The Sun, Mercury, Venus, Earth + The Moon, Mars + two moons (Phobos and Deimos), a small selection of Asteroid Belt bodies (Ceres in the midst of other, smaller, examples), Jupiter + four moons (likely Io, Europa, Ganymede and Callisto), a ringed Saturn + usually one moon (probably Titan) or two (possibly Enceladus or Iapetus, as required), Uranus + four or five 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 + one moon (probably Triton), Pluto + one moon (Charon), four more plutoid/Kuiper Belt objeccts (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 indivudal combinations of green highlights applied to the otherwise repeated diagram.]

[Row 1: Definition:] Traditionalist: Pluto is a planet [Number:] 9 [Highlit: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto]

[Row 2: Definition:] Modern: Pluto is not a planet [Number:] 8 [Highlit: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune]

[Row 3: Definition:] Expansive: Dwarf planets are planets [Number:] 17+ [Highlit: 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 [Highlit: Mercury, Venus, Mars, Jupiter, Saturn]

[Row 5: Definition:] Condescending: Only giant planets are planets; the rest are big asteroids. [Number:] 4 [Highlit: Jupiter, Saturn, Uranus, Neptune]

[Row 6: Definition:] Simplistic: Anything gravitationally round is a planet [Number:] 37+ [Highlit: 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 [Highlit: Venus, Earth, The Moon, Mars, five (non-Ceriese) asteroids and Titan]

[Row 8: Definition:] Regolithic: Anything covered in dirt and ice and stuff is a planet [Number:] [infinity symbol] [Highlit: 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+ [Highlit: 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:] Solipsitic: Earth is the only planet [Number:] 1 [Highlit: The Earth]

[Row 11: Definition:] Judgemental: Only the prettiest ones are planets [Number:] 6 [Highlit: 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 [Highlit: 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+ [Highlit: 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 [Highlit: The Earth and Titan]

[Row 15: Definition:] Universalist: They're all planets [Number:] [infinity symbol] [Highlit: All drawn objects, including The Sun and all other objects including all the moons/asteroids]

[Row 16: Definition:] Existantialist: What if space [next word in italics] itself is a planet??? [Word, in italics:] Duude [Highlit: The whole third column cell]

[Row 17: Definition:] Spiteful: [next word in italics] Only Pluto is a planet [Number:] 1 [Highlit: Pluto]

Trivia

• In the original version of the comic, there were two errors that would alter 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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Discussion

The one currently posted has Pluto highlighted in the second box and not highlighted in the first box. Too hard to tell if it's trolling or a genuine mistake. :-D

Apparently a mistake since it's fixed now. HughNo (talk) 19:59, 14 March 2025 (UTC)

And the first one also has a moon hilighted instead I think?? 162.158.126.5 15:59, 14 March 2025 (UTC)

Was about to write the same. The coloring in the first two lines arund Pluto seem wrong (or mistankingly switched). --172.71.222.246 16:17, 14 March 2025 (UTC)

This, this is the hill I will die on. I was radicalised by this paper: Moons Are Planets: "Scientific Usefulness Versus Cultural Teleology in the Taxonomy of Planetary Science" In short; planets are what planetary scientists study. Round things with the *good stuff*: atmospheres, oceans, volcanoes (of lava or water ice) (see diagram page 53). Pluto, Titan, Ceres, Io and Europa are all in the sweet spot where you're not so small you're just a lump of rocks who happen to be stuck together into a lump, and not so large you're just a mostly undifferentiated mass of fusing hydrogen/helium plasma. And it's consistent with our pre-20th Century understanding of what a planet is, whereas the IAU definition is trying to preserve 19th Century astrology. An amazing read and a strong recommend for anyone who cares about this subject. 172.69.79.138 16:45, 14 March 2025 (UTC)

Does this sort of count as pi-related for pi day? TomtheBuilder (talk) 17:04, 14 March 2025 (UTC)

he doesn't do themed comics anymore 😔 Caliban (talk) 17:12, 14 March 2025 (UTC)

Sure he does. 2962 and 2969 weren't too long ago. Seems like it, though. 172.71.182.222 03:31, 15 March 2025 (UTC)

I was somewhat disappointed to get to the end of the table without seeing either an astrology or Sailor Moon joke. -- Angel (talk) 18:12, 14 March 2025 (UTC)

Is it possible that Uranus is marked under "Empiricist" because of the "Randall has seen Uranus" joke? 172.70.42.178 18:38, 14 March 2025 (UTC)

The "Classical Planets" should be 7, including the Sun and the Moon.

The average distance of the orbit of the Moon around the Earth must be slightly farther away than the orbit of the Sun around the Earth, since the Moon lags behind the Sun a little more each day, but the orbits must cross or we would never have a solar eclipse :P SammyChips (talk) 19:41, 14 March 2025 (UTC)

Wouldn't the Regolithic one depend on the exact definitions of "dirt", "ice", and "covered"? It seems that an argument could be made that the giant planets also count there but have a much thicker atmosphere on the outside, and disqualifying because of the atmosphere could exclude others like Earth depending on the exact threshold used. SammyChips (talk) 19:08, 14 March 2025 (UTC)

Has Randall not seen the sun before?

I'm impressed that he has seen Uranus (unless that actually is a joke), especially if he saw it unaided (apparently it actually can be barely seen with the naked eye if the conditions are incredibly good). SammyChips (talk) 19:36, 14 March 2025 (UTC)

Could the sun be classified as a "world"? --MothWaves (talk) 19:43, 14 March 2025 (UTC)

I assumed he meant "seen directly with my eyes", so that a photograph would not count, but looking through a telescope during an astronomy night at the local University would count. And he hasn't looked *closely* at the Sun, because of the need for eye protection. JimJJewett (talk) 23:49, 14 March 2025 (UTC)

Technically, spacecraft have landed on Mercury, Jupiter, and Saturn. Just not in a survivable manner. Redacted II (talk) 19:37, 14 March 2025 (UTC)

Have we really not sent anything directly into the Sun yet? JimJJewett (talk) 23:51, 14 March 2025 (UTC)

The most "into the Sun" we've done is the Parker Solar Probe, and it hasn't attempted to 'land' there (apart from that being effectively impossible, even beyond the likes of Cassini's final fall "onto" Saturn). It's also very hard to even send things into the Sun, because the direct method would need you to send a craft from Earth backwards at the same speed as the Earth orbits forwards (or very close to that), otherwise all you can do is fall past it and loop back up again. 162.158.74.94 01:00, 15 March 2025 (UTC)

It looks like the Pluto error in Traditionalist and Modernist images were fixed. I now see Pluto highlighted in traditionalist and Pluto unhighlighted in Modern. 172.68.7.91 19:44, 14 March 2025 (UTC)

indeed, it seems fine now, i removed my earlier comment--162.158.233.116 23:06, 14 March 2025 (UTC)

//Jean-Luc Margot wrote a serious planet definition proposal// in 2024 as a starting point for community conversations and welcomes feedback. In 2019 I wrote a small article myself on planet and moon classes simply by size. //Mondklassen "wwwahnsinn"// (in German). 162.158.159.108 19:49, 14 March 2025 (UTC)

I'm disputing that there has never been a formal definition of "planet" prior to 2006 - the ancient Greek definition of "wandering [relative to seemingly-fixed stars] points of light in the night sky" seems formal enough to me. I marked it {{actual citation needed}}. 198.41.227.73 19:52, 14 March 2025‎

I've reworded the sentence to say "in modern times" so we aren't making unfounded and likely-incorrect claims about antiquity. 198.41.227.73 21:19, 14 March 2025 (UTC)

Does anyone else strongly dislike the term natural satellite replacing moon? Under the new nomenclature, only Earth's moon is 'the Moon'. All other moons are now merely natural satellites. Phobos, Deimos, Ganymede, are no longer considered moons. My biggest problem with the new definition is that planets themselves are natural satellites of stars. 172.71.182.225 20:13, 14 March 2025 (UTC)

It seems likely that the Saturnian moon highlighted in the Maritime definition is Titan, since it has liquid seas and lakes on its surface. 172.69.6.5 21:54, 14 March 2025 (UTC)

I've noted in the Transcript that (despite apparently being identical pre-highlight drawings in all other ways, or at least very consistently reproduced), Saturn is given one moon most of the time, but two moons on occasion. Similarly, Uranus's moons (spread from upper-right to lower-left) do-or-do-not include the dot (in one case suffering a highlighting) moving across the face of the planet. From an analytical perspective, I'm wondering if Randall did indeed copypaste the 'normal' iillustration, but then have to manually add in "whoops, I forgot I need to highlight a further item thaat I haven't already drawn" into some of the established copies, touching up where necessary (and maybe where still not necessary too). ...But I'm not sure it matters what he did or did not do. It's just an observation about the result. 172.69.79.190 23:03, 14 March 2025 (UTC)

Yeah, Titan's present in all the diagrams, and a second moon of Saturn shows up when highlighting is necessary. The bonus "Marine Biologist" planet is clearly Enceladus, but the bonus "Judgemental" planet doesn't line up with it: presumably it's one of Saturn's other moons. Which one? My wild guess is Iapetus. 172.68.150.27 01:48, 15 March 2025 (UTC)

Great explanation, thank you, but was it really necessary to include a snide dig at Baby Boomers? Not a BB myself - I'm gen X, if we're using those facile labels - but surely we don't need to encourage intergenerational resentment and conflict. 172.68.174.116 03:22, 15 March 2025 (UTC)
As a historian, I strongly disagree with the snide definition of tradition. (No, not a BB.) 162.158.212.132 07:40, 15 March 2025 (UTC)

That's a direct quote from a prior comic, that whoever wrote it in the first placce ysed, so I've rewritten it to perhaps not look quite so much like some editor's own grudge/snidiness (which it may or may not be, but not without Randall giving justifiable precedent to say it). Maybe can be tweaked further, but it might be a shame to lose the inter-comic referential humour that (regardless of tone) is staple for this site. 162.158.74.109 12:25, 15 March 2025 (UTC)

I believe we're currently missing part of the joke in the mouseover text. Not only is Earth now a star because of human fusion, it's also no longer a planet, because, due to human satellites and spacecraft, it no longer clears its orbit. 198.41.227.42 06:20, 15 March 2025 (UTC)

Isn't the usual singular of criteria criterion? According to my dictionary, a criterium is a type of cycling race.--172.71.26.100 09:46, 15 March 2025 (UTC)

Indeed. Maybe a thinko, though, rather. 172.69.79.139 11:06, 15 March 2025 (UTC)

I am curious why only one of the Galilean moons counts as pretty, and I wonder which one (either Ganymede or Callisto, given where its drawn). They are all pretty to me, I like how surprisingly distinct they look from one another. Terdragontra (talk) 13:18, 15 March 2025 (UTC)

Re title text: With the launch of the JWST, Earth has no longer cleared its orbital neighborhood, right? 172.70.176.57 14:27, 15 March 2025 (UTC)

Citations

I added a bunch of Wikipedia citations. I went by the WP rule (citation needed) of linking the first non-parenthesized instance of a word/phrase. That does make for some awkward things, like lists with only some of the items linked, and the moon link in a mention under Simplistic rather than on the more relevant Lunar. –P₁h₃r₁e₃d₁₃ (talk) 22:34, 14 March 2025 (UTC)

Round vs Spheroidal According to the "simplistic" definition, the rings themselves (also round) are separate planets. If the simplistic definition had merely been "spheroidal" rather than "round", they would not be. I'd love to see a version of the chart where Saturn is green, but the rings are white. 172.71.99.166 23:36, 14 March 2025 (UTC)
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