Low Gravity worlds often ignored in Canon

[foleypt]

I am playing though "The Traveller Adventure" and I am also using the Software "Heaven and Earth" in order to try and flesh out the descriptions for each of the systems. When I get to Zila I notice that it is a small size 2 world and H&E gives it as having 0.235G yet no where in the Traveller adventure (Zila features in 2 episodes of the campaign) is this feature of the planet mentioned! 0.235 is considerably less than normal G and these people are only TL7 so they are not using grav plates in their buildings to compensate. You would imagine the adaptation to life (and Trake wine growing) would be a fairly distinct feature of life on Zila, yet the scenarios don't mention anything about it.

Can I take it as assumed that in classical traveller days they didn't really think about this?

I intend to ignore the H&E value and hand wave that Zila is a dense moon and thus give it say 0.5g, low but not so low as to be the overwhelming feature of the planet.

Also one of my characters is a barbarian from Keng, now I look it up Keng (also size 2) has an atmos of 7, the rules let this happen with a roll of 12, but how can I explain that.. surely a planet that small can't maintain a standard atmosphere? Also how can the people of Keng with TL 3 adapt to such life, wouldn't there be needed exercise machines, medical intervention etc? Not to mention the problems that somebody who lived all there life at low G would have moving to standard g starships etc. Perhaps in any situation where there is low TL and a decent atmosphere value yet the size is very low the best thing to do is assume that the planet is very dense and assign it a G value much higher than what the size alone would give it?

 

[BytePro]

Solar systems are dynamic.

What a system forms as, and what it is at some later date, can generally be 'temporary' on cosmic time scales. Stars evolve; planets form and then their orbits change not to mention the possibility of drastic changes to their very nature over time. Atmosphere's form, change and can disappear.

Research Earth's own geological and atmospheric history and those of other planets in our own system.

Gravity is dependent on distance from center of mass - so a tidally locked 'world' with a larger portion of dense mass (more likely to sunward and something that would have occurred after planet formation, of course) could have a fairly decent regional surface gravity. (And interestingly low gravity on a distant face.) Over time, this planet will likely have other peculiar aspects (esp with influence of other solar bodies) and its orbit change - but that can take many eons.

Ditto the atmo. Atmo 7 on a small world can be maintained for a long time just from geological (and biological) processes. Seismically active worlds (like one with a highly off-center mass distribution ) could be out-gassing and maintaining an atmo for a long time in human generations, though for only a mere blip on the cosmic time line...

 

[Carlobrand]

Size class 2, 3200 Km, half the size of Mars with an Earthlike atmosphere.

Interestingly, Mars per Scouts Book 3 should have a surface gravity of 0.5g, but actually has a surface gravity of 0.376g because it's less dense than Earth (3.9 vs 5.5 g/cm^3). Not much in the way of an iron core - I guess we hogged the iron here.

That could be part of the answer: a higher than expected density, as Bytepro suggests. Iron has a liquid density close to 7 g/cm^3. Imagine a world with a truly massive iron core. It could have a gravity up to 25% higher than expected. Or, a true exotic - a world around a massive lead core. Goodness only knows what could produce that, but such a planet could have a density and gravity 90% greater than a comparable terrestrial planet.

Say Keng, for example, has a massive exotic lead-iron core - the star system is the product of a nearby supernova explosion. (Wave your hands around a lot at this point and try to sound like Carl Sagan - might stop the players from questioning too much.) Surface gravity could be from 0.4 to 0.5g. Even a big enough straight iron core gives it 0.3g. Atmosphere, as Bytepro suggests, is maintained by active geological processes - perhaps a lot of volcanoes and a lot more outgassing than we're used to here on Terra (there is some evidence that Terra's ancient atmosphere may have been up to twice as dense as the present-day atmosphere).

One day it may be Mars, but right now it's a dry little volcanic paradise where the slight scent of egg salad never quite seems to go away, with a population density somewhat lower than Kansas and a West Texas climate. Lovely place for gliding or ballooning, but the flying animals - whooo, they could carry off a toddler! Quetzalcoatlus here had a wingspan of around 10 meters and might have weighed in anywhere from 150kg. to 250kg. Imagine how big something like that cold get on a dry 0.4g planet with standard atmosphere and lots of thermals to carry it. The locals keep some rather big flying predators at bay with single-shot muzzle loaders, possibly very like a blunderbuss, this being a world with no shortage of iron or sulfur. However, their great local advantage is the heavy-boned frame inherited from their 1g ancestors: compared to the light-boned local fauna, humans are tanks.

I get a bit carried away sometimes.

 

[BytePro]

Just re-read The Ringworld Engineers (by Larry Niven - sequel to Ringworld) that I probably haven't read in 20 years...

In the dedication he relates how readers help fix some technical aspects of the ringworld that were not addressed previously. To me the random world gen offers a lot of similar opportunities to address irregularities. (Not saying that odds might not be skewed undesirably at times, but that is the easiest thing to house rule.)

It also covers another point - societies dependent on higher tech than they themselves know how to maintain or create. In Traveller this could be from pre-existing, from better days, and/or from other systems.

A TL7 low grav world - while not industrially setup to manufacture gravitics in general - could still make use of such higher tech in their society. They may make a huge market within parsecs of another system that makes and sells replacements. (And, the gravitic systems in use may have very long lives requiring little to no maintenance.)

 

[foleypt]

Thanks for your replies...

Carlobrand I like your vision of Keng, the player and myself have already incorporated the flying beasties into the back story of how the character got off Keng. The character is from a backward culture on Keng, even by local standards, there the warriors of his tribe prove their braveness by capturing and riding huge Roc flying beasts. Trang set off to find a Roc to prove himself, the bigger the better, he sees a pirate ship landing, one hiding out from some trouble it caused on Freeport, he thinks to himself that if he can tame this giant metal bird nobody in his tribe will doubt his braveness....cue Trangs new life as a press ganged pirate.

What would be the affect of low gravity? at what level would humans be able to medically tolerate and put up with in day to day life without changing drastically how they live? At 0.5g things fall to the ground at half the speed, you can lift twice as much, you can jump twice as high? would you start feeling that you are bouncing around the place like the astronauts on the moon?

I imagine that low tech inhabitants of a low g planet could adjust by having special suits that cause resistance to blood flow, so as to make their hearts work harder and also they could have lead bars in their suits to exercise their muscles. However I think there must be minimums to tolerable long term gravity for human colonisation.

BytePro I also am of the opinion that the TL of a planet represents the manufacturing capabilities of a planet and that it is entirely possible that items of a higher TL would be available for the wealthy, and Zila has some wealthy families and no doubt their houses have grav adjust. I love the idea of a tidally locked planet with uneven gravity, the possibility for drama with chases into the low grav areas (I think they might be low pressure areas too) are great. I just think that it would change the tone too much from the existing scenarios which are about the high law level of the planet and wine growing.

I like the out-gassing idea, but that would mean an atmosphere high in Sulphuric oxide and Carbon dioxide, wouldn't it?

Here is an idea, could a high axial spin on a planet, say caused you the collision between two proto-planets at planet formation that gave Zila its unusually dense core, could high axial spin lead to higher atmosphere retention and apparent gravity? In the same way that artificial gravity can be induced on a space station by sniping it?

 

[BytePro]

Yep - Earth's own spin does generate centrifugal forces - though quite negligible compared to the force of gravity. We are spinning at > 1,600 kph IIRC - and there is a measurable effect globally (at the equator compared to the poles) - notably our weather patterns (from motion and sun exposure) and the bulge of the oceans...

However, 'Spinning' a world sized object enough to create any useful artificial gravity, I suspect might generally rip the planet apart (not to mention what happens at the poles regarding the desired effects). The surface effects on a sphere (besides making an oblate spheroid like Earth) would be very interesting (like the fluid whorl direction we see between hemispheres - not to mention the global weather patterns). Artificial gravity also has cardiovascular implications (also sopite syndrome (sp?) may apply...).

Long term low-g also drastically affects the human skeletal system (bone loss) - besides the fluid issues (and us being big bags of water...). Though, genetic adaptations can 'solve' that problem in a Sci-Fi setting.

Out-gassing can be any atmo mix you desire - and be from various processes (not just direct ejecta from volcanoes). There are plenty of natural materials that can create breathable atmospheres - and natural processes (biological and even catalytic) that can filter otherwise toxic gases.

As mentioned, outgassing doesn't necessarily mean volcanoes, but using Earth's as an example, the composition of gases varies greatly - most common is actually just water. SO2 can be useful for warming (like CO2) and can also be broken by biological means (and silicates). Nitrogen separated from ammonia from thermal processes (tectonic?) may be a good way to add inert gas... and look at Archaea - its role in Ammonia/Nitrogen cycle was not really understood till just a few years ago!

Looked at objectively - Earth's atmo could be considered implausible. We certainly still consider the observed atmo's of our system's other planets implausible till we come up with new theories and can actually validate them with probes. (Look up Titan's nitrogen atmo - or Mars' lack of limestone.)

RE: imported tech like gravitics - such things may be purchased at a colony level. So extrapolating equipment costs would not be linear - and buying power could be quite immense. (Like Walmart dictating their costs for products - lock in a system to your market, then dictate prices...).

 

[Carlobrand]

... The character is from a backward culture on Keng, even by local standards, there the warriors of his tribe prove their braveness by capturing and riding huge Roc flying beasts. Trang set off to find a Roc to prove himself, the bigger the better, he sees a pirate ship landing, one hiding out from some trouble it caused on Freeport, he thinks to himself that if he can tame this giant metal bird nobody in his tribe will doubt his braveness....cue Trangs new life as a press ganged pirate.

I like that.

Keng: tech level 3, charismatic oligarch, high law level ...

I'm seeing an early gunpowder agrarian culture huddled around the few bodies of water, led by that charismatic oligarch but bedeviled by your "backward culture" tribalists who roam the dry region. Your tribalists are supremely adapted to dry region life, making excellent use of the dry-region-adapted plants and animals to meet their food and water needs as well as to provide other resources such as clothing, weapons, tents - or whatever it is they use for shelter - etc. Of course, the dry region being what it is, the tribalists are rather scattered. They may raid each other to keep competitors out of the territory in which they hunt or herd.

The agrarians would have a higher population density, giving them a defensive advantage, but they are ripe targets for raiding along the frontiers where irrigated lands give over to dry lands. That's likely the best source of knives, pots, and other useful metal items for your tribalists; although they could probably do without the items, there'd be a certain status in having a knife or a pot acquired in a daring raid. Despite the slight tech advantage of the agrarians, they've no hope of ever bringing the tribalists under control because, with that low water rating, there's just so comparatively much dry territory and so comparatively little agrarian land. They rally around their oligarch, whose classically Napoleonic-style army prevents the tribalists from getting too bold - and enforces iron-fisted control to maintain the peace and the oligarch's authority in the face of constant tension over water rights and water distribution.

However, that army's style of fighting is less effective in the dry region, where keeping the unit supplied with water is a serious challenge and supply trains are vulnerable to raids. His compact formations would work well to overcome the militias that agrarian villages could assemble and to drive off the occasional tribalist raiding party, but they'd have serious trouble bringing the mobile tribalists to battle, and they are vulnerable to sniping - especially if your tribalists are riding flyers.

Scouts rated the world government by the the oligarch and the area he controls because they didn't think of the tribalists and the dry region as being of any consequence, there being much more opportunity for commerce with a compact agrarian community than with a scattering of tribes.

... What would be the affect of low gravity? at what level would humans be able to medically tolerate and put up with in day to day life without changing drastically how they live? At 0.5g things fall to the ground at half the speed, you can lift twice as much, you can jump twice as high? would you start feeling that you are bouncing around the place like the astronauts on the moon?

We've learned quite a bit about very low gravity, and of course we know life at 1g, but there's really been no opportunity for science to explore what it might be like to live at half a g - no way to produce it for more than short periods. So, I honestly have no idea if the medical issues associated with microgravity would also apply at 0.5g. I expect there'd be wider individual disparities: you could stay reasonably strong if you stayed reasonably active - with the running and jumping and such - and you'd look pretty impressive by Terran standards, being able to run longer and faster and jump higher on Keng. Your tribalists should do fine, as should the typical agrarian field hand. However, the sedentary types, the scribes and clerks and such, are likely to be weaker than they might be here on Earth because the little activity they do get is against a lighter gravity.

... I like the out-gassing idea, but that would mean an atmosphere high in Sulphuric oxide and Carbon dioxide, wouldn't it?

Yes, a smelly place, Keng is. By canon, Keng circles a G5 yellow giant, on the cold side of the habitable zone, so the boosted CO2 would help warm the place more to Earth standard. However, there's an errata that says yellow giants are supposed to be plain old Sol-type yellow main sequencers. Keng would circle on the warm side of the habitable zone for a G5 main sequencer, and the extra CO2 would make it a rather hot little world. It's up to you.

 

[foleypt]

I love how with just a few bare numbers and a bit of imagination we can build world rich with potential for exploration and adventure.

My players would probably buy anything in term of explanation, I am the most scientifically literate of us, but if I can't build for myself a 'believable' explanation of how the planet's characteristics mesh together then I can't pass it on the the players.

Keng I now get, Keng I want the player's to visit now..of course being stuck in Aramis subsector they are fed up with low tech dirtballs and are desperate for a planet with a decent tech level (if only to buy cool gadgets at a affordable price).. so I imagine it might be a while before Trang takes a sentimental journey home.

Zila I am a bit unsure of still. Cannon has it as a moon of a gas giant, the seas covering half its surface suffer huge tides, it is a corrupt democracy with franchise restricted to large land owners, it has a restrictive law level and obstructive bureaucracy. It is an agricultural world, a producer of quality wine but has a poor E starport. Ok, I think I can get the sociological part, with the electors acting like feudal overlords on their wine estates and uninterested in any progress for the world because their life is good. The government bureaucracy left to itself, as long as it keeps out of the way of the powerful electors, has drowned itself in petty laws and red tape.
The physical setting is a bit harder to imagine, I guess we can go for a heavy core and hence bump the G up to 0.5, however what with outgassing volaneos and S=2 in atmos.. I'm having some difficulty trying to imagine this planet as the estates and wineries depicted in The Traveller Adventure

 

[BytePro]

Uh, SO2 is very important in wine making (for like the last half millennium at least!)

No reason for high SO2 or even CO2 in final product. That is a grade school oversimplification - reality is much more varied and complex. Thankfully - otherwise we'd all be dead and the CO2 in our atmo would make Earth a seething hell hole.

 

[foleypt]

The Role of Sulfur Dioxide in Wine

So it is, thanks!

Also When Life Gives You Volcanoes, Make Wine


Ok, so sorted for the trake growers on dense cored, volcanic and stinky atmosphered 0.5g Zila!

 

[BytePro]

Glad to be of some help!

Just for future reference regards atmo's on low g worlds:

Even a tiny planet is pretty darn big = and miles of 'crust' can provide a lot of filtering (both natural, like silicates, and living) ... so outgassing does not have to mean super high pressure eruptions (ala Io's). And a volume of atmo doesn't just instantly vacate low gravity (which, again can be regionally higher), especially if a region of cooling exists at high altitude (look to our own atmo).

Ammonia oceans on a cool side of a tidally locked world, might be superheated by thermals (especially towards the transition between star facing and not) and thus support liberating large amounts of nitrogen. A tidally locked world, just like our tidally locked moon, is more likely to exhibit tectonic activity on the side of the larger body, including the 'boundary' to the far side. (Using tidally locked examples due to the small size and applicability to moons...)

Like any process - it would have a 'limited' lifetime - but, in human scales, all that would be needed would be relative stability for thousands and thousands of years to seem good enough for a UWP code. In our own system we've seen lots of evidence for drastically different atmos over the billions of years we estimate. (Regardless of whether there was enough time for evolution based on our single sample, many appeared to last for geological times...)

Note, the LRO last year confirmed that the dark side of the moon had a volcanic eruption only a billion years old - which also trashed most of the theories of the moon's interior as it implied a still liquid crust at least up to that time. The moon is our closest neighbor, yet until last year we didn't even have a very good map of the far side (though earlier missions had been there, LRO is the first to do dedicated full surface mapping - my dad actually fabbed one of the instruments on that one )!