^Which is an entirely separate complaint. One can draw one's own conclusions about the quality of the series, but how can you not be aware that the intention of the prequel was to show the origins of the familiar elements of the Trek universe? I mean, that's pretty much what prequels do.
Also a possibility that TOS was trying to emulate the stellar types of O-B-A-F-G-K-M with a similar classification for planets. Why O-B-A-F-G-K-M? Why that order? Why seven letters? What does each stand for? Apply those same answers to "Class M" planet, I suppose. Maybe TOS planets were classified T-Y-F-K-M-O-P or any other assorted arrangement.
For what it's worth, I found a fairly comprehensive and seemingly accurate Wiki entry about Trek planet classes: http://en.wikipedia.org/wiki/Class_M_planet Basic layout:
Originally, in the 1860s when spectroscopy was first used to distinguish stars into different spectral types, they were labeled alphabetically from A to P in order of the strength of their hydrogen Balmer lines. Later, once we gained more understanding of the hydrogen atom and the nature of its emissions, it was determined that different factors affected the strength of the hydrogen lines and that it wasn't a straight increase with temperature -- cooler stars didn't have enough energy to boost the H atoms' electrons out of the ground state, and hotter stars had enough energy to ionize the atoms altogether so there were no electrons to jump and produce Balmer lines. So the strongest lines were from stars around 10,000 K, dropping off in either direction, and that meant the alphabetical classification based on Balmer line strength didn't represent a meaningful temperature progression. Early in the 20th century, Harvard astronomers revised the classification system, dropping redundant categories and reordering them by temperature, leaving OBAFGKM from hottest to coolest.
Right on. I know about the color/temperature meanings of the stellar letters. Perhaps TOS envisioned an equivalent seven-letter/temperature classification for planets. Or they needn't be sequential letters nor even seven letters.
^Except we keep discovering so many new, different types of planets and dwarf planets that it would take a lot of letters to classify them.
Star Trek has provided a possible answer. In "The Bonding", I learn that the planet is Class M, Type IV. I think within each classification that there are differences, and these types represent these differences, but, in the overall scheme, these planets fundamentally meet the criteria for that classification.
Don't be silly. Planetary classes are for stupid planets! I was going to suggest a Class and Category scale with letter and number. But "Mudd's Women" also mentions a "class J" cargo ship. How do they keep it all straight?
Then too, there is actually such thing as cthonian planets http://www.space.com/13828-alien-planets-kepler-telescope-infographic.html http://www.centauri-dreams.org/?p=26133 http://www.centauri-dreams.org/?p=25952
From the original pitch, they were to explore habitable planets with (E)arth-(M)ars, or E-M, conditions, so it was probably originally "em"-class planets.
Upthread, I listed what the third revision of the Star Trek Writers/Directors Guide had to say about Class M, and I described why in the 1970's I assumed -- with others -- that the "M" in "Class M" stood for "Mars". Here's what the original pitch for Star Trek said, created by Gene Roddenberry, first draft, dated March 11, 1964: (If I missed any references to "Class M" or "Mars", it's because I had to search without the aid of a computer. I omitted some text regarding the "Parallel Worlds" concept. Any errors entering this text are my own.) As with the Star Trek Writers/Directors Guide, the original pitch said, in so many words, that "Class M" stands for "earth-Mars conditions" [sic]. However, the spelling of "Class M" in the pitch was always with the capital letter "M". If it was ever spelled "em"-class, as cleverly suggested by Darkwing, then it was spelled that way before the first pitch was written. It's good to know that the phrase "earth-Mars conditions" goes all the way back to the original pitch.
Let's step back from the alphabet classification system and ask a different question: what is it that they are classifying with these letters? We're assuming that "Class M", versus "K Type", etc., is a broad classification of all of a given planet's characteristics. Why assume that? I always looked upon Spock's reports on planets being "Class M" or whatever as an indicator on what kind of gear a landing party would have to wear (assuming surface conditions allowed for a landing party). So "Class M" would mean normal Starfleet fatigues were in order. By the "K Type" report Norman gave in "I, Mudd", it sounded like Muddworld and Elba II were similar in that they would require space suits or pressure domes. (But Marta was able to live long enough exposed outside to be hauled out and blown up.) So maybe the Alphabet Soup was a handy indicator for how starship captains should outfit their landing parties or colonization expeditions. Consider it a "life support" indicator. Probably a standard developed by ancient Vulcan space travellers to determine whether or not it was worth landing on a given planet.
I doubt "Class M" stood for anything originally. As CorporalCaptain shows, it was included in the original 1964 pitch document -- and there's a lot of stuff in there that Roddenberry just pulled out of his hat, like the alleged equation for how many inhabited worlds there might be in the universe, which was pure gibberish. So I'm sure "Class M" was just some random term Roddenberry made up to sound technical -- like the reference in the next paragraph of Captain April's orders, "You will patrol the ninth quadrant, beginning with Alpha Centuri and extending to the outer Pinial Galaxy limit." Let's see... not only is there no such thing as the Pinial Galaxy, but Alpha Centauri is misspelled, there can only be four quadrants, and two points only define a line, not a volume of space. But that didn't matter; what mattered is that it sounded like it meant something to the characters, that it gave a feel of the texture of the show's world. More to the point, the pitch document wasn't meant to be published, it was just meant to sell the idea of the show to network executives, most of whom wouldn't have known a galaxy from an asteroid. So it didn't have to make sense. It didn't even have to accurately reflect what the show would become (or else we would've been following the voyages of the starship Yorktown all this time). So "Class M" was just gibberish, like "Pinial Galaxy" and his ersatz Drake Equation. The only difference is that it's gibberish he decided to keep using. If things had gone slightly differently, we might be debating the etymology of "Pinial Galaxy" right now.
Or the definition of the third quadrant of the vernal galaxy? The classification scheme is a mess. We have gas giants under two classifications: an alphabet soup and a number soup. We have classifications referring to size, to atmosphere, and to general characteristics of an astronomical object. I would say Gene Roddenberry was ignorant of astronomical subjects as much as the NBC execs. In 1965, Mariner 4 had reached Mars and was transmitting data back to NASA that revealed that Mars was not Earth-like. Though it is in its infancy, I think we are seeing how planets might be classified in the future. They are being classified on size, mass, atmosphere, and land-sea ratios. I might have missed a few. And, I think that there will be one body regulating the classification scheme so that it doesn't become a confusing mess.
Whatever Gene's level of ignorance, the original pitch was written well before the Mariner-Mars probes were launched in 1964. As far as I know, the phrase "Earth-Mars conditions" never made it into the show.
How then to explain the 1967 Writer's Guide, which treats Mas as having similar conditions to Earth? Timo, I know that you were involved in the making of Star Trek: Star Charts. Do you remember having discussions about the planetary classification? Was it raised what the classification for Neptune would be?