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lpetrich
2018-Nov-30, 11:25 PM
We all know about Star Trek's class M planets, I'm sure, planets as habitable as ours currently is. But the series has many lesser-known planet types, most likely because such planets are not very nice places to visit. It likely inspired by the spectral-type system of stars: OBAFGKM. From several sources, I have pieced together a classification. Planetary classification | Memory Alpha | FANDOM powered by Wikia (http://memory-alpha.wikia.com/wiki/Planetary_classification), Ex Astris Scientia - Planet Classification (http://www.ex-astris-scientia.org/database/planet_classes.htm), Star Trek planet classification (https://en.wikipedia.org/wiki/Star%20Trek%20planet%20classification) A problem is that a major source, "Star Trek Star Charts: The Complete Atlas of Star Trek" (Geoffrey Mandel 2002) has doubtful canonicity. But that aside, I've found


A: Gothos
B: Mercury
C: Pluto
D: Small airless rocky planetoid: Earth's Moon
E, F, G: proto-Earth-sized
H: Earth-sized with an arid surface
I: Gas supergiant, larger than J
J: Gas giant: Jupiter, Saturn
K: Earth-sized, cold: Mars, Mudd
L: Earth-sized, marginally habitable: several
M: Earth-sized, habitable for humanity: Earth, numerous others
N: Earth-sized, hot: Venus
O: Covered with water
P: Covered with water-ice
Q: Very changeable due to an eccentric orbit or star variability
R: Rogue planet (one that orbits no star)
S: Gas ultragiant, larger than I
T: Gas ultragiant, larger than S
Y: a "demon" planet, one with very nasty surface conditions
X, Z: other "demon" planets

Before about 500 million years ago, the Earth itself was pretty much class L, because of its low atmospheric-oxygen levels (about 10% - 20% present-day in the mid-Proterozoic, and essentially 0% in the Archean and Hadean).

[0707.2895] Mass-Radius Relationships for Solid Exoplanets (https://arxiv.org/abs/0707.2895) has some calculated-structure curves in its Figure 4. The largest sizes are reached for masses around 1000 Earth masses (3 Jupiter masses). H-He: 11 Earth radii, water: 5 Re, rock (MgSiO3): 3.5 Re, iron: 2.7 Re. Jupiter is about as as big as a planet can get without something puffing it up. So J is as big as it gets, and I, S, and T are not physically possible without some artificial puffing up. But if "size" refers to mass, then I, S, and T are possible, even if smaller in space dimensions than J. They could fade off into brown dwarf stars.

DaveC426913
2018-Dec-01, 04:37 AM
You'd think they'd have a class just for Risa and Rubicun III*.

*"It seems they'll make love at the drop of a hat. Any. Hat."
-Tasha Yar

lpetrich
2018-Dec-01, 07:56 PM
Your proposed classification of "pleasure planet" would include not only those two but also the Shore Leave planet, I think. But that is orthogonal to the classification that I had posted about in my OP.

KaiYeves
2018-Dec-02, 01:14 AM
You'd think they'd have a class just for Risa and Rubicun III*.

*"It seems they'll make love at the drop of a hat. Any. Hat."
-Tasha Yar

That would be a cultural/anthropological classification of a planet's inhabitants, not an environmental classification of the planet itself as is being discussed here.

DaveC426913
2018-Dec-02, 05:53 AM
That would be a cultural/anthropological classification of a planet's inhabitants, not an environmental classification of the planet itself as is being discussed here.
Ya think?

(I felt free to take it in the direction of my choosing, since the OP didn't ask any questions.)

KaiYeves
2018-Dec-02, 06:31 AM
Ya think?

(I felt free to take it in the direction of my choosing, since the OP didn't ask any questions.)

Right, sorry, I hope I didn't seem rude.

lpetrich
2018-Dec-04, 05:14 AM
I will attempt to sort out Star Trek's planet classes.


Gas giant: J ... Jupiter, Saturn
Earth-sized:

Hot: N ... Venus
Temperate:

Habitable: M ... Earth
Borderline: L ... past Earth
Ocean: O
Desert: H

Cold:

Rocky: K ... Mars
Icy: P


Small, airless: D ... Moon

Tom Mazanec
2018-Dec-04, 12:47 PM
Then there is the Non-Luminary World Classification Scheme from the OAUP, which is actually based on 2018 science:
https://orionsarm.com/eg-article/491c78b89879b

DaveC426913
2018-Dec-04, 02:55 PM
Right, sorry, I hope I didn't seem rude.

;)

eburacum45
2018-Dec-05, 05:43 PM
The Star Trek classification system seems to be missing classes for gas giants as small as Uranus and Neptune (or smaller) and for super-earths or superterrestrials, rocky planets much larger than Earth. Curiously enough, a very large number of the thousands of planets that have been discovered since the Star Trek classification system was written fall into those two categories.

Chuck
2018-Dec-05, 08:28 PM
Maybe they reclassified gas giants as subdwarf stars.

lpetrich
2018-Dec-08, 07:13 AM
The Star Trek classification system seems to be missing classes for gas giants as small as Uranus and Neptune (or smaller) and for super-earths or superterrestrials, rocky planets much larger than Earth. Curiously enough, a very large number of the thousands of planets that have been discovered since the Star Trek classification system was written fall into those two categories.
Seems to me that much of this classification is finer-grained for what might be interesting to visit, or at least what might seem interesting to visit, and coarser-grained for less interesting places. That means a lot of detail for Earth-sized planets that are not too far from habitability, and not much detail elsewhere.


Maybe they reclassified gas giants as subdwarf stars.
Why might they do that? That seems highly unlikely to me.

lpetrich
2018-Dec-08, 07:44 AM
HEC: Periodic Table of Exoplanets - Planetary Habitability Laboratory @ UPR Arecibo (http://phl.upr.edu/projects/habitable-exoplanets-catalog/media/pte) has this classification:

Miniterrans: 10^(-5) to 0.1 Me, 0.03 - 0.4 Re
Subterrans: 0.1 - 0.5 Me, 0.4 - 0.8 Re
Terrans: 0.5 - 5 Me, 0.8 - 1.5 Re
Superterrans: 5 - 10 Me, 1.5 - 2.5 Re
Neptunians: 10 - 50 Me, 2.5 - 6.0 Re
Jovians: > 50 Me, > 6 Re

Me and Re are the mass and radius of the Earth. PHL's classification also divides planets into hot, warm (habitable), and cold. I'd prefer calling habitable medium or temperate -- giving "class M" temperatures. In our Solar System:

Miniterrans: H: Mercury, M: The Moon, C: (numerous)
Subterrans: H: ., M: Mars, C: .
Terrans: H: Venus, M: Earth, C: .
Superterrans: H: ., M: ., C: .
Neptunians: H: ., M: ., C: Uranus, Neptune
Jovians: H: ., M: ., C: Jupiter, Saturn

Exoplanet statistics are dramatically different.

I searched Inventions and Ideas from Science Fiction Books and Movies at Technovelgy.com (http://www.technovelgy.com/) for other science-fiction planet classifications, without success.

Noclevername
2018-Dec-08, 11:38 AM
The Star Trek classification system seems to be missing classes for gas giants as small as Uranus and Neptune (or smaller) and for super-earths or superterrestrials, rocky planets much larger than Earth. Curiously enough, a very large number of the thousands of planets that have been discovered since the Star Trek classification system was written fall into those two categories.

The ST system dates to before the actual discovery of exoplanets. It's an artifact of its time, back when we thought our solar system was typical.

Chuck
2018-Dec-09, 04:53 AM
Only planets they can build sets for get classified.

eburacum45
2018-Dec-10, 10:48 PM
As well as the NOLWOCS system that Tom Mazanec mentioned (which is itself an adaptation of John M Dollan's Planet Classification List (https://web.archive.org/web/20070318122352/http://arcbuilder.home.bresnan.net/PCLMaster.html)), we at Orion's Arm have also attempted to create another, more methodical classification system.
https://orionsarm.com/eg-article/51f1109b96a76
But even this one has some shortcomings. I'm fairly sure that the 'phase space' of planetary types is larger than anything we've imagined yet.

eburacum45
2018-Dec-10, 10:53 PM
On another note, here's a table showing the different types of planet found in Space Engine, some of which are quite interesting (I think this is a translation from Russian, so might not be entirely clear to a native English speaker)
http://spaceengine.ucoz.org/_fr/0/2958096.jpg