local gravity vs. Imperial 'standard doors'

[kilemall]

We had the gravity discussion just a few months ago, I was under the impression G was largely a 'done deal', that planetary density was a minor factor compared to sheer size.

So G would be largely determined simply by world size with a few things like 'superdense neutronium core placed by Grandfather's prankster kids and powered up' type anomalies.

 

[Timerover51]

The problem with the gravity figures in Scouts and The Traveller Book is that they all assume that planets have the same density as Earth, which is not the case in our Solar System, and probably will not be the case in other solar systems. Mars is size 4 in its UWP, but instead of a gravity of 0.5 that of Earth, it actually is 0.375 (per NASA), the same as a size 3 planet. The Moon is a size 2 planet, but its gravity is only 0.166 of Earth (per NASA), rather than 0.25 as per the Traveller charts. A planet of size 10/A with a density equal to that of Mars would have a surface gravity of 0.89 approximately of Earth, while to have a planet of size 10/A with a surface gravity equal to Earth would have a density of 4.4 grams per cubic centimeter compared to Earth's 5.5 grams per cubic centimeter.

 

[Magnus von Thornwood]

Not a problem for T5!

The problem with the gravity figures in Scouts and The Traveller Book is that they all assume that planets have the same density as Earth, which is not the case in our Solar System, and probably will not be the case in other solar systems. Mars is size 4 in its UWP, but instead of a gravity of 0.5 that of Earth, it actually is 0.375 (per NASA), the same as a size 3 planet. The Moon is a size 2 planet, but its gravity is only 0.166 of Earth (per NASA), rather than 0.25 as per the Traveller charts. A planet of size 10/A with a density equal to that of Mars would have a surface gravity of 0.89 approximately of Earth, while to have a planet of size 10/A with a surface gravity equal to Earth would have a density of 4.4 grams per cubic centimeter compared to Earth's 5.5 grams per cubic centimeter.

Somewhere in the page 500s or so there is a chart with variable densities, so in T5 at least you can adjust the local gravity.

Actually, I think it might be around either 530 or 512ish, but may be wrong, books are still packed so can't check.

 

[Whipsnade]

But one real-world example of environment change on people comes from another GDW book, Space: 1889 [Heliograph reprint] page 28: "army statistics showed a serious decline in the size and health of recruits from 1800 to 1900, as the slums replaced the country villages as prime sources of young men."

That was due to nutrition, not environment.

So it seems to me there would be plenty of time for people to adapt to local gravity in the Marches, and give the Imperial Navy Board of Starship Architects many headaches.

However it seems to you is fine IYTU. The jury is still out on the OTU however because what AM;4 says and what we all thought it said aren't actually the same thing.

Nailing down the gravity of all worlds in Charted Space as a function of world size, while presenting some benefits, just seems like an accounting exercise most will ignore.

Exactly.

 

[aramis]

We had the gravity discussion just a few months ago, I was under the impression G was largely a 'done deal', that planetary density was a minor factor compared to sheer size.

So G would be largely determined simply by world size with a few things like 'superdense neutronium core placed by Grandfather's prankster kids and powered up' type anomalies.

Gravity varies significantly by average density of body.

G = M/D²
G in gravities
M in earths
D distance in earth radii
All expressed in earths.

Mass = r³d
r = radius
d = density
Both can be expressed in earths.

Substituting into the formula to get surface g's
G = r³d/r²
Simplifying
G = rd

Noting that comets have densities of between 0.6 and 2 g/cm³, and Earth is about 5.5, expressing cometary density in earths is 0.1 to 0.36 or so...
Note that the inner core is about 13 g/cm³, or 2.3 D_e, outer core between 10 and 12 g/cm³, and the mantle about 3 and 5 g/cm³, and the ocean between 1.4 and 1.01 g/cm³..

Simplifying for playability...
So, a metalic core is about 2.4 D_e, liquid outer core about 2 D_e.
The silicate layer is about 0.55 to 1 D_e, let's average and call it 75%
Ices run from about 0.1 to a peak at around 0.25 D_e... (1.4 g/cm³)...

I think I can cobble up a calculator in Javascript to do it easily enough...
but not tonight. Tonight I'll use a calculator.

If we assume similar proportions... radii and density (in earths) for an approximation
Earth inner solid core 1220km 2.4 D_e 0.16 M_e
Earth liquid outer core 3400 km, 2 D_e 0.29 M_e
Earth surface 6,371km, 0.75 D_e 0.63 M_e
I get about 0.94 M_e, which means I need a better estimate on the density.

But note, for a simpler methodology...

G= {[0.86*(S/8)³]+[1.15*(S_core/8)³]}/S²

Here's a handy table of Masses (in Earth Masses) by proportion of metallic core.

UWP Size	0	1	2	3	4	5	6	7	8	9	10	0	0	0	0.02	0.06	0.14	0.28	0.49	0.77	1.15	1.64	2.25
1	0	0	0.02	0.06	0.15	0.28	0.49	0.77	1.15	1.64	2.25
2	0.01	0.02	0.03	0.07	0.16	0.29	0.5	0.78	1.16	1.65	2.26
3	0.04	0.05	0.06	0.11	0.19	0.33	0.53	0.82	1.19	1.68	2.29
4	0.11	0.11	0.12	0.17	0.25	0.39	0.59	0.88	1.26	1.74	2.35
5	0.21	0.21	0.23	0.27	0.35	0.49	0.69	0.98	1.36	1.84	2.45
6	0.36	0.36	0.38	0.42	0.5	0.64	0.84	1.13	1.51	2	2.6
7	0.57	0.57	0.59	0.63	0.71	0.85	1.05	1.34	1.72	2.21	2.82
8	0.85	0.85	0.87	0.91	0.99	1.13	1.34	1.62	2	2.49	3.1
9	1.21	1.21	1.23	1.27	1.35	1.49	1.7	1.98	2.36	2.85	3.46
10	1.66	1.66	1.68	1.72	1.8	1.94	2.15	2.43	2.81	3.3	3.91

[tc=11]Metal Core Size[/tc]
[TR]

So, in finding the mass, multiply it by 8, then divide by the UWP size, and you get surface gravity.

http://frigg.physastro.mnsu.edu/~eskridge/astr102/density.jpg

 

[Timerover51]

Somewhere in the page 500s or so there is a chart with variable densities, so in T5 at least you can adjust the local gravity.

Actually, I think it might be around either 530 or 512ish, but may be wrong, books are still packed so can't check.

The only chart I can find in T5.09 is on the bottom of page 440, and the example of a Size 5 planet with a density of 1.1 times that of Earth having a gravity of 1 is wrong. The correct figure is 0.685 of Earth Gravity.

 

[kilemall]

Where the hell were you when I was getting beat on for bringing up the density issue?

http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=35743&highlight=gravity+density

My concept was you should be able to work backwards from world size and atmosphere to work out a relative G to allow for that level of atmosphere to be retained.

Yes I know atmo retention is a series of factors not just G, but if one has an active core helping retain the atmosphere well then we know it has to be X density and power at a minimum.

 

[G. Kashkanun Anderson]

Note the use of the word "tend". When producing "fluff text", GDW rarely wrote in absolutes.

'Physically, the Zhodani are tall and lithe, averaging 2.0 meters in height and massing upwards of 90 kilograms.' -- Traveller Adventure 6: Expedition to Zhodane

I believe this is also, word-for-word, what the JTAS Contact! article on the Zhodani said, too. Two meters is right around 6' 7" in Old Earth Units. So 'tend' nothin' -- Zhodani are tall.

The Darrians are even taller, if you can believe that. According to the CT Darrians Alien Module (page 15), Darrians 'average slightly more than 2 meters in height', whilst averaging a mere 78 kilos in mass -- or 12 kilos (about 25lbs) less than the average Zhodani.

Either way, both of them tower over most genetically pure Solomani, let alone a Vilani (who are, canonically, slightly shorter than a Solomani) or a Geonee (who are waaaaay shorter than any of them).

All of this corresponds with the relative sizes of their homeworlds, of course, ranging from the Geonee homeworld of Shiwonee being a UWP Size A (borderline superterrestrial) to the Darrian homeworld of Daryen being a UWP Size 4 (roughly Mars-sized). In this case I want to emphasize, however, that these are all homeworlds in an evolutionary sense, not just some random place of birth. In other words, Traveller does firmly stake itself to the belief that creatures evolving in lower gravity environments will tend towards increased height over those evolving in higher gravity environments, but it doesn't (AFAIK) push that idea over to the notion that simply growing up on a low gravity world will make someone tall and lithe.

 

[Reban]

'Physically, the Zhodani are tall and lithe, averaging 2.0 meters in height and massing upwards of 90 kilograms.' -- Traveller Adventure 6: Expedition to Zhodane

I believe this is also, word-for-word, what the JTAS Contact! article on the Zhodani said, too. Two meters is right around 6' 7" in Old Earth Units. So 'tend' nothin' -- Zhodani are tall.

The Darrians are even taller, if you can believe that. According to the CT Darrians Alien Module (page 15), Darrians 'average slightly more than 2 meters in height', whilst averaging a mere 78 kilos in mass -- or 12 kilos (about 25lbs) less than the average Zhodani.

Either way, both of them tower over most genetically pure Solomani, let alone a Vilani (who are, canonically, slightly shorter than a Solomani) or a Geonee (who are waaaaay shorter than any of them).

Just for comparison present day pure-blood Solomani on Earth average 178.25cm (Males average 185.6 and females average 170.9, although another source gives 174.46cm as average human height).

So yes that crick in my neck is due to the Zho's being taller than me a Sollie, the buzzing in my brain however.....

Our height of course also changes over the course of a day. Height has a lot to do with health as well as environment. Scientific American had an article saying height was 60-80% heritable through the genes, which is surprisingly low to me.

Here's an interesting question: what part of the Zhodani makes them "tall". Is it long legs, a long narrow trunk or torso, a long neck, high domed skull, or a combination of some or all of the above? And if so, what caused those specific adaptations?

This Wikipedia article is worth a read.

 

[Condottiere]

It's genes in a well nurtured environment.

The Dutch were reputed to be the tallest people during the early modern period, got put on short rations and the Americans got that distinction, then following the Great patriotic War, reclaimed their crown.

Not to mention the East Asians now sprouting like bamboo shoots.

 

[jcrocker]

Now we can add 'edition wars' to the fun, here's a quote from MegaTraveller Referee's Companion, page 59, talking about the Zhodani:

"Their height and physical build are both consequences of Zdant's 0.85G surface gravity."


Granted, the Zhodani and Darriens have all been hanging out on low-g worlds for 300,000 years, but there are worlds in the Marches settled for 1000+ years, and older worlds in First Imperium space, and that's got to have had some effect.

Meh. Grandfather tinkered with their height genes. He liked these high loft ceilings, you see, but hated changing the lightbulbs up there, and the hover vehicles kept getting stuck in the peak. So he went to Terra, grabbed people, and stretched them genetically. Problem solved.

 

[aramis]

The Traveller Logbook (Judges Guild, for CT) gives bonuses to Str and End for high G and penalties to same for Low G, and inverse to height and weight, and mods to Education for TL... and adds rolls for height and weight (weight is given in kg/m of height..., from 17 to 60)... but it's not canonical.

It's just another example of available sources mirroring the nivenesque principle that high G is stronger and more enduring...

 

[Timerover51]

I have also seen speculation that High-G is going to result in shorter life spans due to the added stress on the heart.

 

[aramis]

I have also seen speculation that High-G is going to result in shorter life spans due to the added stress on the heart.

I've seen studies on chickens (including by NASA) that imply the same. Personally, I think End should be inversely affected by the strength mod, if one uses it.

 

[jcrocker]

Since the Vilani are defined as long-living, and they're high-g natives, should we just quietly ignore any evidence to the contrary?

 

[aramis]

Since the Vilani are defined as long-living, and they're high-g natives, should we just quietly ignore any evidence to the contrary?

We know there was genetic engineering by the ancients, and a lack of local microbiome that was compatible with the proto-Vilani...

Which can overcome the "Raised on X" issue.

 

[whulorigan]

Granted, the Zhodani and Darriens have all been hanging out on low-g worlds for 300,000 years, but there are worlds in the Marches settled for 1000+ years, and older worlds in First Imperium space, and that's got to have had some effect.

But keep in mind that there is a difference between people who are Ancient's transplants who effectively evolved on a world, and those who have simply colonized a world in the (relatively) recent past from another technological society.

People who have been on a world for 300,000 years will think of their world's gravity as "normal", and will have evolved in its g-field. People who are Imperial (or other) citizens who colonize a world from a previous technological civilization may very well choose to maintain a different (and more "normal") gravity within their biomes or residences by choice if gravitics is available and economical enough at the time of their initial settlement. Just because the world is 0.5g doesn't mean the locals won't modify it to a level more to their liking.

Now lower-tech colony worlds would be a different matter . . .

 

[Whipsnade]

But keep in mind that there is a difference between people who are Ancient's transplants who effectively evolved on a world, and those who have simply colonized a world in the (relatively) recent past from another technological society.

Now, now. Don't be logical.