planetary classes

[Pauln6]

But presumably outside that mass range, gravity would be too great or too low to be class M anyway, proceeding on the assumption that a smaller planet's magnetic field would be too weak within the habitable zone to sustain its atmosphere long enough for life to develop. Although having said that, I think Venus' magnetic field is not all that strong presumably its atmosphere is so thick because of all the volcanic activity?

I suppose a smaller planet would be able to maintain an atmosphere if it has a regular enough supply of icy meteorites to restock it but its hard to see that that could be maintained long enough for complex life to develop.

There are probably only so many classifications that occur in nature so other classifications would need to be for unusual planets that require further investigation. If the demon planet is classified as such because its atmosphere and radiation make it dangerous to both ships and personnel even with protection then those should be considerations taken into account in the classification system.

[Christopher]

It's believed that Earth might be toward the low end of the size range for habitable planets, because smaller planets wouldn't have plate tectonics, which is necessary for recirculating carbon from the atmosphere or something like that. An exception might be a large moon of a Jovian in the habitable zone, where tidal stresses might drive plate tectonics in a smaller world than could otherwise have it. But there are questions about whether such large moons would be possible, except in rare cases of initially independent planets being captured into Jovian orbit.

[throwback]

We are discovering new types of planets constantly. Along with those mentioned, astronomers have discovered diamond planets (http://www.ibtimes.com/discovery-dia...y-world-847633) and Hot Neptunes (http://www.centauri-dreams.org/?p=1263).

Here is a real world list of planet types - http://en.wikipedia.org/wiki/List_of_planet_types

Like the situation with dinosaurs - where certain types of species will never be discovered because of where they lived, that there may be planet types that we might never discover.

* http://blogs.smithsonianmag.com/dino...the-dinosaurs/

[CorporalCaptain]

SchwEnt wrote:

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I'm an old timer TOS fan, way before "Minshara" came into the picture. Alls I ever knew was Class M, no explanation given. But way back when I was a kid...

Why M? Only thing I could think of was M being smack in the middle of the alphabet. Class M were the planets just right for human life.

Like some kind of Goldilocks thing, I thought the 26 letter alphabet was the gamut of planets. Class A planets were way too cold, Class Z planets were way too hot, but Class M planets were just right (smack in the middle).

Arbitrary? Probably. But at least I didn't invent some Minshara planets to explain the "M".

Back in the good ol' days--a.k.a. the 1970's--I assumed (and as I recall, along with other fans, too) that the "M" in "Class M" stood for "Mars", because the Star Trek Writers/Directors Guide said, in so many words, that "Class M" stands for "Earth-Mars conditions".

From the Star Trek Writers/Directors Guide, series created by Gene Roddenberry, third revision, April 17, 1967:

Star Trek Writers/Directors Guide wrote:

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We do not have space suits available or other forms of environmental suits for hostile planet surfaces. These may be obtained for special scripts but keep in mind that we generally restrict our missions to "Class M" planets (approximating Earth conditions).

[...]

Be creative, but practical here, too. Remember, "Class M" planets will be often similar to many parts of Earth -- and with societies duplicating or intermixing almost any era in man's development. Jungle backgrounds exist on back lots, so what about primeval worlds? Or a pioneer-Indian type culture? Lovely parkland exists locally, so do unusual highly modern buildings, so do farms.

[...]

I understand the concept of most landings taking place on planets approximating Earth-Mars conditions. But will we never get to a planet where gravity or atmosphere is a problem?

Yes, assuming the right story. Also some story will undoubtedly take us outside our vessel into space for repairs or to investigate some strange object there. But generally we will avoid space helmets and weightlessness since such tales would more legitimately concern Earth's present era of space travel. The aim of our format is drama and entertainment based on character rather than on details of technology and hardware.

[Forbin]

Christopher wrote:

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^"Not everything has to tie in?" An odd comment, given that the whole point of ENT was to show the origins of the Trek universe we knew.

...in as ham-handed a way as possible.

"Reed Alert!!"

[Christopher]

^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.

[SchwEnt]

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.

[137th Gebirg]

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:

Class A, B and C
Typically small, young planets whose class depends on their age and solidity of their cores.

Class D
Class D objects are planetoids like asteroids and some moons. Regula, the site of the underground second stage of the Genesis experiment in Star Trek II: The Wrath of Khan, is a Class D planetoid. The USS Voyager also encountered Class D planets in the Delta Quadrant, one in the Star Trek: Voyager episode "Gravity" and one in the episode "Emanations".

Class E, F and G
Typically, Proto-Earth-sized planets whose class depends on their age and solidity of their cores.

Class H
Class H planets appear in the series as harsh desert worlds. The planet Tau Cygna V visited by the USS Enterprise-D in the Star Trek: The Next Generation episode "The Ensigns of Command" was designated as a Class H world.

Class I
Class of gas giant, larger than Class J, and smaller than Class S and T.

Class J and T
Class J and Class T planets are gas giants. Class J are smaller than Class T which are considered "super", or "ultra", gas giants. In the Star Trek: Deep Space Nine episode "Starship Down", the USS Defiant enters the atmosphere of a Class J gas giant to rescue the crew of a Karemman ship attacked by the Jem'Hadar. The USS Voyager encounters a Class T Super-Giant in the Delta Quadrant with "radiogenic" rings in the Voyager episode "Good Shepherd".

Class K
Class K planets are barren worlds with no native life. However, through terraforming, they can be made into Class M worlds. In the original Star Trek series episode "I, Mudd", the planet Mudd was designated in dialogue as Class K.

Class L
Class L planets are barely habitable worlds with primitive ecosystems. In "The Chase", the planet Indri VIII is indicated in dialogue as Class L. In "The 37s", the planet on which Amelia Earhart and others are stranded is a Class L planet with an oxygen–argon atmosphere. In "Muse", the planet on which B'Elanna Torres' shuttle crash lands is described as a Class L planet, which also supports Bronze Age humanoid life. In "Timeless", the USS Voyager' crashes into a Class L planet with an arctic climate. In "The Ascent", Quark and Odo crash-land on a desolate Class L planet.

Class M
from the Vulcan term "Minshara," is a fictional classification for planets and planetoids in the Star Trek science fiction media franchise.

Their atmospheres are composed of nitrogen and oxygen and have an abundance of liquid water necessary for carbon-based life to exist. Extensive plant and animal life often flourishes; often, a sentient race is also present. Earth is a textbook example of a Class M world; other Class M planets that appear throughout the franchise include Vulcan, Cardassia Prime, Bajor, Betazed, Romulus, Ferenginar, and Qo'noS.

In fiction, Class M planets are similar to those suggested to be found in the real-world astronomical theory of life supporting planets found within the habitable zone (HZ), sometimes also referred to as the 'Goldilocks' zone. The Earth Similarity Index, a scale used in planetary science, includes within its classification of habitable planets (hClass) a "Class M", where the "M" stands for mesoplanet (not to be confused with Asimov's mesoplanet proposal), i. e., a planet with moderate (as necessary for liquid water) temperatures, more technically speaking: the thermal surface requirements necessary to support complex (multicellular) Earth-like life.

Class N
Class N planets have a reducing environment and are barren and rocky with extremely high surface temperatures caused by thick atmospheres containing carbon dioxide and corrosive sulfides. In "Night Terrors", Class N environments were mentioned as the ideal places to use oxidizer-free explosives. The Tholian are said to have come from an N Class planet in the Star Trek: The Lost Era book The Sundred. The game Star Trek: The Next Generation - A Final Unity mentions that Class N planets are more related to Class M with the key difference being a higher ratio of water to land.

Class O and P
Planets covered almost completely with water (class O), or water–ice (Class P).

Class Q
Planets with continually changing environments caused by peculiar orbits, an orbit around a variable output star, or some other factor which causes conditions to drastically change over time.

Class R
A rogue planetary body, which is one that does not orbit a star but drifts freely in space. However, not all rogue planets are classified as Class R; for instance, in Star Trek: Deep Space 9 episode "The Search", the Founders homeworld in the Omarion Nebula is referred to as a "rogue" Class M planet. But this is probably a rare situation as most planets that don't belong to a star system would not be able to support life.

Class S
Class of gas giant smaller than Class T and the next larger size up from Class I.

Class T
The largest class of gas giant. Smaller gas giants are, in order of decreasing size, Class S, I, and finally J.

Class Y
Class Y planets are referred to as "Demon" worlds, where surface conditions do not fall into any other recognized category. Such worlds are usually hostile and lethal to humanoid life. If life develops on these worlds they usually take on many bizarre forms, like living crystal or rock, liquid or gaseous physical states, or incorporeal, dimensional, or energy-based states. In the series, examples of Class Y "Demon" planets include Tholia, the "Silver Blood" planet discovered by the USS Voyager in the Delta Quadrant in the episode "Demon" and later mentioned in "Course: Oblivion", and the home world of the incorporeal Medusans.

Class X and Z
Reserved for other designations of "demon" planets.

[Christopher]

SchwEnt wrote:

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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?

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.

[Ronald Held]

Christopher beat me to that explanation. There are now letters for cooler stars than M.

[SchwEnt]

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.

[Christopher]

^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.

[throwback]

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.

[Metryq]

Don't be silly. Planetary classes are for stupid planets!

throwback wrote:

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Star Trek has provided a possible answer. In "The Bonding", I learn that the planet is Class M, Type IV.

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?

[Ronald Held]

Planetary letter and numbers seems like the stellar spectral class system.