Numbered planets: what method?

[at Quark's]

Yes, and the first planet discovered around, say, George B would be George Bb, the next would be George Bc, etc. (The body itself is "a," so its first companion is "b.")

True, though such lower cases don't always denote planets. For example, take the Castor stellar system, which consist of three main stellar components, Castor A, B, and (later discovered) C. However, still later each of these were discovered to be close binaries in themselves, so now we have six stars, Castor Aa, Ab, Ba, Bb, Ca and Cb. So supposing that castor Aa was again a binary or had a planet (unlikely since Aa and Ab orbit each other in 9.2 days, but supposing) would that then be Castor Aaa/Aab?

 

[Christopher]

True, though such lower cases don't always denote planets. For example, take the Castor stellar system, which consist of three main stellar components, Castor A, B, and (later discovered) C. However, still later each of these were discovered to be close binaries in themselves, so now we have six stars, Castor Aa, Ab, Ba, Bb, Ca and Cb.

Yes, that's right. Basically exoplanets are treated as components of a binary/multiple system the same way stars are. In a binary star, the larger (or the first discovered?) is a and the other one is b, and then c and so on, so if you have a star and a planet, that's also a binary system and the same nomenclature is used.

So supposing that castor Aa was again a binary or had a planet (unlikely since Aa and Ab orbit each other in 9.2 days, but supposing) would that then be Castor Aaa/Aab?

Hmm, good question. Castor Aaα (Alpha)?

 

[scotpens]

And what happens if they "reclassify" Mercury because it doesn't have an atmosphere? Or Venus because it lacks a moon? Or Saturn, because technically it's about the density of a milkshake?

Less than that, actually. Saturn has a lower density than water.

 

[Christopher]

And what happens if they "reclassify" Mercury because it doesn't have an atmosphere? Or Venus because it lacks a moon? Or Saturn, because technically it's about the density of a milkshake? Why do they all get to be planets and Pluto doesn't?

Then science gets better, because it learned more and adapted accordingly. That is literally what science does. It adapts itself to new knowledge, rather than clinging to its past mistakes. That's the whole thing that makes it powerful. In science, discovering you were wrong about something is awesome. It's great, because it lets you learn whole new stuff, and come closer to getting it right.

As I said, Pluto was never a good fit for the "planet" category to begin with, because it was too different from the other planets. Scientists only called it that for lack of a better alternative. The dwarf planet category is that better alternative, a whole new class of objects that have their own distinct nature, which is cool and exciting. I mean, before, we thought we had a pretty good handle on the Solar System and the big discoveries were over with. Now we realize there's a whole new class of potentially thousands of worlds out there waiting to be discovered, and that is incredibly cool, and it frustrates me that people refuse to see how amazing that is because they're hung up on Pluto alone. This makes Pluto more exciting than it ever was as a "planet," because it was a pitiful also-ran as a planet, and now it's the harbinger of a whole new era of discovery. How is that not wonderful???

"Get to be planets" is a nonsensical way of putting it, because it's not a value judgment, just a category. It's like asking why something "gets to be" a noun instead of a verb, or a lake instead of a river. There's no prestige or hierarchy involved, it's just coming up with clearer descriptions for what things are and how they differ from each other.

Hell, the whole reason the 2006 debate happened is that we never actually had a good definition for "planet" in the first place. It was just a leftover label from antiquity and we stuck it onto things out of force of habit. We never really defined where the limits were for something being a planet or not a planet, and the discovery of things like dwarf planets and brown dwarf stars, things that sit on the fuzzy borders between the categories we thought we knew, are requiring us to put more thought into defining where those borders fall. And that is absolutely, unambiguously a good thing, because we're learning more about the universe and that is the bloody point. It's not a beauty contest. There are no winners and losers. There's just learning more.

 

[MAGolding]

Personally, I'm with you. If I were doing the numbering, Pluto would be Sol IX. So apply the question to Ceres, Eris, and our other little balls of rock which were never granted planet status in the first place.

Ceres was considerd a planet when first discovered. The first four asteroids were considered planets when first discovered. Some astronomers even classified the asteroids down to number 15 as planets, until in the 1850s they wre reclassified as minor planets and asteroids.

https://en.wikipedia.org/wiki/List_of_former_planets

Wikipedia has a list of objects which were formerly considered to be planets for longer or shorter periods of times. So at different times there would have been different numbers of planets listed in astronomy books that you might think.

Perhaps I should give a brief, a very brief, discussion of the names of stars and extra solar planets in science and science fiction.

For countless thousands of years humans on Earth have been giving proper names to various stars, often based on their apparent positions in the constellations imagined in the stars. So any particularly bright star will have many different proper names.

A man named Bayer published a star atlas in 1603. The plates depicting each constellation gave lower case Greek letters to the naked eye visible stars in each constellation, usually, but not always, in order of declining apparent brightness. So astronomers got into the habit of designating stars by the their Greek letters (often spelled out in the Latin alphabet) and the Latin genitive case of the constellation name.

A century later Astronomer Royale John Flamsteed created a star catalog. The naked eye visible stars in each constellation were given numbers in order of their increasing right ascension coordinates, followed by the Latin genitive case of the constellation name.

And probably hundreds of star catalogs have been published since, some with hundreds of stars, some with hundreds of thousands of stars, and I think a few with hundreds of millions of stars, though most of the stars in our Milky Way Galaxy have no designation in any catalog.

A star is typically designated by the full name or standard abbreviation of a catalog, followed by its number in that catalog. Well known stars can have designations in dozens of different catalogs.

Thus the star that fans usually think that Vulcan orbits has a Bayer designation of Omicron 2 Eridani (the 2 is in superscript position) and a Flamsteed designation of 40 Eridani, and many other catalog numbers.

In this millenium the International Astronomical Union created a committee which has been given official proper names to naked eye stars, usually using names which have been used for centuries or millennia in some Earth cultures.

Many stars are double or multiple star systems. Individual stars in those systems are known by the system name or designation followed by A, B, C, D, etc. in order of luminosity. If a component of a system is later found to be itself two stars, their original designationis followed by a, or b in lower case.

The convention for exoplanets discovered orbiting other stars is usually to give them lower case Latin letters, starting with b, in order of their discovery. If astronomers gave the letters in order of distance from the star, they would often have to reletter planets after new planets closer tot he star were discovered.

40 Eridani is a triple star, consisting of 40 Eridani A, B, and C. 40 Eridani A now officially has the name of Keid, which was givenn to the entire system centuries before the three separate stars were discovered.

So the first planet discovered to orbit Omicron 2 Eridani.A, or 40 eriani A, or Keid, will be designated Omicron 2 Eridani.A b, or 40 eriani A b, or Keid b. At present i here is no confirmed planet orbiting that star.

The four big moons of Jupiter were discovered by Galileo in 1610 and by Simon Marius soon after. Simon Marius named them Io, Europa, Ganymede, and Callisto in increasing order of distance from Jupiter, but astronomers rarely used them

The Galilean moons of Jupiter (Io, Europa, Ganymede, and Callisto) were named by Simon Marius soon after their discovery in 1610.[26] However, these names fell out of favor until the 20th century. The astronomical literature instead simply referred to "Jupiter I", "Jupiter II", etc., or "the first satellite of Jupiter", "Jupiter's second satellite", and so on.[26] The names Io, Europa, Ganymede, and Callisto became popular in the mid-20th century,[27] whereas the rest of the moons remained unnamed and were usually numbered in Roman numerals V (5) to XII (12).[28][29] Jupiter V was discovered in 1892 and given the name Amalthea by a popular though unofficial convention, a name first used by French astronomer Camille Flammarion.[19][30]

The other moons were simply labeled by their Roman numeral (e.g. Jupiter IX) in the majority of astronomical literature until the 1970s.[31] Several different suggestions were made for names of Jupiter's outer satellites, but none were universally accepted until 1975 when the International Astronomical Union's (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII,[32] and provided for a formal naming process for future satellites still to be discovered.[32] The practice was to name newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus) and, since 2004, also after their descendants.[19] All of Jupiter's satellites from XXXIV (Euporie) onward are named after descendants of Jupiter or Zeus,[19] except LIII (Dia), named after a lover of Jupiter. Names ending with "a" or "o" are used for prograde irregular satellites (the latter for highly inclined satellites), and names ending with "e" are used for retrograde irregulars.[33] With the discovery of smaller, kilometre-sized moons around Jupiter, the IAU has established an additional convention to limit the naming of small moons with absolute magnitudes greater than 18 or diameters smaller than 1 km (0.62 mi).[34] Some of the most recently confirmed moons have not received names.

https://en.wikipedia.org/wiki/Moons_of_Jupiter

The Roman numbering system for satellites arose with the very first discovery of natural satellites other than Earth's Moon: Galileo referred to the Galilean moons as I through IV (counting from Jupiter outward), refusing to adopt the names proposed by his rival Simon Marius. Similar numbering schemes naturally arose with the discovery of multiple moons around Saturn, Uranus, and Mars. The numbers initially designated the moons in orbital sequence, and were re-numbered after each new discovery; for instance, before the discovery of Mimas and Enceladus in 1789, Tethys was Saturn I, Dione Saturn II, etc.,[28] but after the new moons were discovered, Mimas became Saturn I, Enceladus Saturn II, Tethys Saturn III and Dione Saturn IV.

n the middle of the 19th century, however, the numeration became fixed, and later discoveries failed to conform with the orbital sequence scheme. Amalthea, discovered in 1892, was labelled "Jupiter V" although it orbits more closely to Jupiter than does Io (Jupiter I). The unstated convention then became, at the close of the 19th century, that the numbers more or less reflected the order of discovery, except for prior historical exceptions (see Timeline of discovery of Solar System planets and their natural satellites); though if a large number of satellites were discovered in a short span of time, the group could be numbered in orbital sequence, or according to other principles than strictly by order of discovery. The convention has been extended to natural satellites of minor planets, such as (87) Sylvia I Romulus. The outer irregular satellites of Jupiter (VI through XII) were left officially unnamed throughout this period, although as stated above some unofficial names were used in some contexts.

From 1975 to 2009, the International Astronomical Union was assigning names to all planetary satellites, and Roman numerals were usually not assigned to satellites until they are named. (An exception is Saturn's moon Helene, which received the Roman numeral XII in 1982, but was not named until 1988.) During this period, the use of Roman numeral designations diminished, and some are very rarely used; Phobos and Deimos are rarely referred to as Mars I and Mars II, and the Moon is never referred to as "Earth I". However, since 2015 some moons have again been numbered without being named, starting from Jupiter LI.

https://en.wikipedia.org/wiki/Naming_of_moons#Roman_numeral_designations

As pulp science fiction developed various conventions in the first half of the 20th century, alien planets around different stars could be named many ways. They could have proper names given by their intlligent natives or Earth Earth explorers. And their stars could be known by native names, or names given by Earth explorers, or by real names used on Earth at the time the stories were written.

Science fiction developed a convention that planets could be known by the human or native name or catelog designation of the star, followed by a Roman numeral in order of increasing orbital distance from the star. So in our solar system Mercury would be Sol I, Venus Sol II, Earth Sol III, and so on.

For example, in E.E. Smith's Second Stage Lensman the planet Tralle is also known as Trallis III, and the planet Onlo in the same star system is also kown as Trallis IX.

And in the early 20th century there were less than 31 moons known in the solar system, some of them with Roman numberals in orbital order and some of them in order of discovery.

Thus it is a historical question which science fiction writers originated the science fiction numbering convention. Second Stage Lensman was orginally serialized in astrounding Science Fiction NObember 1941 to February 1942, but I have only read the book version, first published in 1953, and I don't know if the planetary numbers were added when it was revised for the book.

Anyway, Star Trek more or less follows the naming conventions of science fiction. Many stars have proper names, some from Earth, many stars have Bayer designations, many stars have designations in probably fictional catalogs, etc. And similarly many planets are known by proper names, and others are known by the name or designatinof the star followed by a number. I don't know if we ever see a Roman numberal on screen, or if the characters merely give the planetary numbers in English..

When they discuss which planet to search in "Spock's Brain", the inhabited planets are described as the third, fourth, and sixth, planets, I think. And possibly they are numbered with Roman numerals or Arabic numerals on the screen.

Of course many Star Trek writers were not well educated in astronomy nor science fiction fans, and so some of the star and planet names and designations used in various Star Trek productions are rather strange.

The Ex Astris Scientia site has a discussion of many problems with star names in Star Trek.:

https://www.ex-astris-scientia.org/inconsistencies/bayer-names.htm

And remember that this has been a very, very short discussion of star and planet names in astronomy, science fiction, and Star Trek.

 

[MAGolding]

Reclassification and redefinition of terms as knowledge advances happen frequently within science. It's just that there's usually less of an overlap with public consciousness about it.

I don't even think that the scientific committee that decided this cared too much whether the public (i.e. the rest of the world) would keep calling Pluto a planet or not- they were probably just concerned with getting their scientific definitions set up in such a way that they would be most useful for future scientific work. To which they had every right.

At that time it was expected that a lot more planetary mass objects (planemos) - massive enough to be gravitationally rounded - would be discovered in the outer solar system and be classified as planets. And apparently the committee thought that would be bad idea. Maybe they thought it would overtax the brains of astronomy students to remember the names or 20 planets or something, even though most astronomers know the designations of hundreds of astronomical objects without any trouble.

Astro geologists interested in the geology of other world probably classify all planemos (planetary mass objects) as planets for their purposes, whether those planemos are major planets, dwarf planets, minor planets, moons/natural satellites, or rogue planets in interstellar space. By that definition the solar system has dozens of known planets aleady..

I don't know if dwarf planets are numbered in the Star Trek planetary designation system.

I note that in Star Trek different definitions of planets may be used in different eras, thus making "planets" many times more numerous in some eras than in others. So if various objects get added to or subtracted from the list of planets in a system, does their Roman numeral change?

Less than that, actually. Saturn has a lower density than water.

Saturn has an average density less than that of water. It has an incredibly high density in its innermost core, and most of saturn's volume has a density even less than the average density you mentioned, with a density gradient getting denser and denser the closer to the core.

 

[Christopher]

At that time it was expected that a lot more planetary mass objects (planemos) - massive enough to be gravitationally rounded - would be discovered in the outer solar system and be classified as planets. And apparently the committee thought that would be bad idea. Maybe they thought it would overtax the brains of astronomy students to remember the names or 20 planets or something, even though most astronomers know the designations of hundreds of astronomical objects without any trouble.

I think a good way to approach it would be to start treating the Solar System as subdivided into distinct regions. There's the Inner System, which contains the four terrestrial planets Mercury, Venus, Earth, and Mars. The Main Asteroid Belt separates that from the Middle System, home to the gas giants Jupiter and Saturn and the ice giants Uranus and Neptune. Beyond them lies the Kuiper Belt, the beginning of the Outer System, which contains an uncounted number of dwarf planets and smaller icy objects, and potentially at least one undiscovered large planet. There's no need to memorize every object, since it's taught more in terms of regions and their overall character. You don't need to know the name of every mountain in a range, just the name of the range and how it relates geographically to other regions.

 

[Timelord79 (he/him)]

Then science gets better, because it learned more and adapted accordingly. That is literally what science does. It adapts itself to new knowledge, rather than clinging to its past mistakes. That's the whole thing that makes it powerful. In science, discovering you were wrong about something is awesome. It's great, because it lets you learn whole new stuff, and come closer to getting it right.

As I said, Pluto was never a good fit for the "planet" category to begin with, because it was too different from the other planets. Scientists only called it that for lack of a better alternative. The dwarf planet category is that better alternative, a whole new class of objects that have their own distinct nature, which is cool and exciting. I mean, before, we thought we had a pretty good handle on the Solar System and the big discoveries were over with. Now we realize there's a whole new class of potentially thousands of worlds out there waiting to be discovered, and that is incredibly cool, and it frustrates me that people refuse to see how amazing that is because they're hung up on Pluto alone. This makes Pluto more exciting than it ever was as a "planet," because it was a pitiful also-ran as a planet, and now it's the harbinger of a whole new era of discovery. How is that not wonderful???

"Get to be planets" is a nonsensical way of putting it, because it's not a value judgment, just a category. It's like asking why something "gets to be" a noun instead of a verb, or a lake instead of a river. There's no prestige or hierarchy involved, it's just coming up with clearer descriptions for what things are and how they differ from each other.

Hell, the whole reason the 2006 debate happened is that we never actually had a good definition for "planet" in the first place. It was just a leftover label from antiquity and we stuck it onto things out of force of habit. We never really defined where the limits were for something being a planet or not a planet, and the discovery of things like dwarf planets and brown dwarf stars, things that sit on the fuzzy borders between the categories we thought we knew, are requiring us to put more thought into defining where those borders fall. And that is absolutely, unambiguously a good thing, because we're learning more about the universe and that is the bloody point. It's not a beauty contest. There are no winners and losers. There's just learning more.

Pluto would not even fit antiquity definition of planet.
The term is derived from the Greek word for “wanderer” and refers to bright pricks of light moving about the sky, in contrast to fixed stars, on a specific plain.
That’s not what the word encompasses, but it’s what the ancients refered to with the term.
Pluto is outright invisible to the naked eye and needs a fairly powerful telescope to be recognized.
Under that system Jupiter’s 4 Galilean moons have more rights to be called planets.

 

[1001001]

And remember that this has been a very, very short discussion of star and planet names in astronomy, science fiction, and Star Trek.

Dude...it's 30 paragraphs.

 

[Christopher]

Pluto would not even fit antiquity definition of planet.

Well, sure, but by that standard, neither would Uranus or Neptune, both of which were only discovered with the invention of telescopes.

As I said, the problem is that the term "planet" was just accepted tradition and had never really had a detailed scientific definition, because there was no need for one. Pluto, the odd one out that didn't really fit, was the first clue that the traditional (non-) definition was in need of clarification. But since it was just one object, astronomers just let the anomaly linger. Once we discovered that there were multiple other objects of the same type as Pluto, and that we were likely to discover dozens or hundreds more, that made it urgent to clarify our definitions.

Dude...it's 30 paragraphs.

Yes, that's MA's point -- that even a long post by the standards of a BBS is still just a brief overview of a complex subject.

 

[1001001]

Yes, that's MA's point -- that even a long post by the standards of a BBS is still just a brief overview of a complex subject.

Yes, thanks so much for explaining it to me.

 

[Maurice]

Yes, thanks so much for explaining it to me.

It's his way...

 

[137th Gebirg]

As he said.

 

[Maurice]

Pluto would not even fit antiquity definition of planet.
The term is derived from the Greek word for “wanderer” and refers to bright pricks of light moving about the sky, in contrast to fixed stars, on a specific plain.

By that standard Neptune wouldn't be a planet, either, since, like Pluto, it can't be seen without a telescope. Uranus is very very occasionally visible to the naked eye, but so infrequently it might as well not qualify either.

 

[XCV330]

Yes, that's MA's point -- that even a long post by the standards of a BBS is still just a brief overview of a complex subject.

It's not a complex subject, not that complex. Clearly, there is a difference between windbaggery and give-and-take discussions.

To put it into context; the actual IAU resolution on the definition of a planet is actually shorter than that exposition. Read it, it's a real kick in the chest:

https://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf

 

[Christopher]

To put it into context; the actual IAU resolution on the definition of a planet is actually shorter than that exposition.

Which is a meaningless point to make, because of course that definition was not pulled out of thin air, but was a distillation of a much more lengthy process of discussion in which many complex issues were debated and weighed and many thousands of paragraphs were written and exchanged. The final definition was approved after multiple proposals, discussions, and commentaries, which I followed avidly at the time. I recall there being a fair amount of controversy over the final definition, particularly the out-of-the-blue insertion of the language about a planet "clearing its orbit" (which if taken strictly would exclude most planets from the definition, including Earth) and the contradictory language stating that a dwarf planet was somehow not a planet. IIRC, the feeling at the time was that it should just be a first approximation, a work in progress to be refined with further analysis and discussion. It's surprising that it still stands unchanged 15 years later.

 

[XCV330]

It's surprising that it still stands unchanged 15 years later.

Not really. It works. It kept TNO's out of consideration since more and more were being found. (excluding some potential "X" which would be expected to clear its path of objects It would likewise prevent future Oort Cloud objects from being catalogued as planets, though I also suspect it will be a long time before an oort cloud object is ever positively id'd (incoming comets notwithstanding) . The definition of dwarf planet works very well.

Thank you, Oddish! Where does it stop when people decide to just 'reclassify' things?

science hopefully does not stop. more was learned along the way.

Archer IV! Somehow one of "two planets" named for Jonathan Archer, when it should be the sun named for him with a minimum of 4 planets.

unless Archer is the name of some gas giant planet and Archer IV is the fourth moon of said planet. Or, less likely ARCHER was just some kind of cataloging system that didn't get very far (the way there are planets and stars named EPIC (like the beautifully named planet EPIC 206317286 c) that are from the EPIC database of objects taken from the K2 mission of the Kepler spacecraft. Whew.

And what happens if they "reclassify" Mercury because it doesn't have an atmosphere? Or Venus because it lacks a moon? Or Saturn, because technically it's about the density of a milkshake? Why do they all get to be planets and Pluto doesn't?

As far as I know there haven't been any attempts to seriously issue these classifications on density of atmosphere or having a satellite. You can put the strawman away. You might as well bemoan the terrible people who threaten to de-galaxy Andromeda because it isn't riding a unicycle.

 

[Christopher]

Not really. It works. It kept TNO's out of consideration since more and more were being found.

What has that got to do with science? It just feels political, an arbitrary rule to avoid making too great a change to our assumptions of how many planets there are. Science should never be afraid to render our assumptions obsolete. What the hell does "out of consideration" even mean in a scientific context? Science is supposed to consider everything. Discovery requires a completely open mind, not arbitrary made-up rules to keep things "out of consideration." What a horribly unscientific phrase that is.

The definition of dwarf planet works very well.

Except it is bizarre and self-contradictory to call something a dwarf planet while claiming it's not a planet. Dwarf stars are still stars. Dwarf galaxies are still galaxies.

 

[XCV330]

What has that got to do with science? It just feels political, an arbitrary rule to avoid making too great a change to our assumptions of how many planets there are. Science should never be afraid to render our assumptions obsolete. What the hell does "out of consideration" even mean in a scientific context? Science is supposed to consider everything. Discovery requires a completely open mind, not arbitrary made-up rules to keep things "out of consideration." What a horribly unscientific phrase that is.




Except it is bizarre and self-contradictory to call something a dwarf planet while claiming it's not a planet. Dwarf stars are still stars. Dwarf galaxies are still galaxies.

 

[Hofner]

By that standard Neptune wouldn't be a planet, either, since, like Pluto, it can't be seen without a telescope. Uranus is very very occasionally visible to the naked eye, but so infrequently it might as well not qualify either.

I hope I'm not stating the blindingly obvious but the ancients didn't consider Earth a planet so there were only five planets.

Robert