Story research - need to know what is affected by a lower gravity environment

[chrispenycate]

Titan is an unusual example of a planet sized moon with an atmosphere because of its very unusual circumstances. I think the tidal forces of Jupiter keeps the core hot and the volcanos erupting and the atmosphere going. It’s gravity is very low because it’s not a very dense moon and I strongly suspect that in the absence of Jupiter it would be airless. I’m still holding to my tipping point of around 70% earth gravity to keep an atmosphere on a planet, clearly in the absence of interfering gas giants that are making a mockery of my newly invented rule. As Chrispy has stated, losing an atmosphere takes time, as in Mars may have been very nice in the past so if your timing was right we could have danced on the surface of Mars. A nice way of saying, when it comes to SciFi all bets are off, even my brand new 70% rule.

However, Titan as an example does offer other possibilities for generating and renewing an atmosphere on a body with low gravity. I can’t imagine a body that relies on volcanos’ like on Titan to be very useful to us, as in breathing and running around the surface, but could easily develop other types of life. Even Titan is a candidate for some life, but I think the odds may be against it.

But, (rule number two today, I’m on a roll) I’m going to say that having a moon in orbit around the planet would be good for plate tectonics and general recycling of and renewing of elements in an atmosphere. Additional (possible) side benefits of tides, a stable axis and a pretty night time sky.

Half an inch tall and six feet wide really does bring a new meaning to the word “fat”.

Hmm. Meant to reply to this one some time before, but had to reread Forward's Saturn Rukh first (now, there's a book full of tell, not show, and technical details about how everything works, with minimal interest in characters' motivation or emotions. I happen to love it.)

Titan, unless they've moved it while I wasn't looking, is in orbit round Saturn, so Jupiter's gravitational pull is unlikely to stress it much. As Saturn's "surface" gravity is about the same as Earth's (Saturn might actually have a surface somewhere deep in the ridiculous pressure zones. I'm not sure how we could ever find out. One thing's for sure, the solid part is not very big, if it exists at all; the low density tells us that much. But everything we can see or test is gaseous.) the 'heating by gravitational stress' hypothesis is non-proven (actually, even Io in the Jupiter system isn't stressed by the big planet's gravitational field, which simply holds it in orbit, but tidal forces from the other moons plus, maybe, electro-magnetic forces from Jupiter's powerful magnetic field. We don't know enough – let's go there and find out, eh?)

And saying 'volcanoes belch it out' or 'there is a giant methane ocean constantly replenishing the atmosphere' is not a sufficient explanation for the gas' existence in the first place. The universe is a vast puzz-saw jiggle, and we're still missing a lot of edge bits. In fact there's only one little bit that's reasonably well filled in, and that's missing a lot of pieces. I'm assuming most of that blue is sky, but they omitted putting the picture on the box, so there could be an enormous blue monster…

 

[Bowler1]

Titan, unless they've moved it while I wasn't looking, is in orbit round Saturn

Alright, alright... I'll put Titan back!

Having actually checked up on some facts today I've also discovered Saturn's magnetic field protects Titan from the solar wind, which would help explain how it keeps it’s atmosphere. Anyway, off to Titan we go, your space ship or mine… yours I think, my tax has run out.

 

[Spiegal]

Interestingly enough despite being a boiling hot, crushing, acid raining hell hole Venus is one of the likelier candidates for human habitation in the solar system.
I wrote a quick bit of universe fluff for a story about miners living in a floating city in huge upper atmosphere.

The buoyancy of oxygen at the sweet spot in Venus' atmosphere would be able to hold a complex of rooms aloft without any additional balloons or propulsion (within reason of course) the temperature is well within comfortable limits and the pressure is 1 atmosphere, same as earth. Going outside for a stroll wouldn't be too nice though the only protective gear you would need is a respirator and some kind of protective overcoat.

It would make a pretty nice setting for a disastrous skydive!

 

[psychotick]

Hi Spiegal,

Not so sure about that. Air at one atmosphere isn't really that boyant. If it was we'd all be floating around instead of walking. And my understanding is that probes which have landed on Venus' surface (and lasted for all of a couple of minutes as I recall) have actually landed. Even at ninety atmospheres they didn't float.

However in my view it is easily more likely than Mars to be habitable - after some terraforming which would basically have to turn the organic content of the acid bath air into something inert. But it isn't hard to see that certain bacteria like life forms could be seeded in the upper atmosphere to do this job, and once the air is cleaned up the temperature would drop, hopefully to the point where you coul have liquid water, and if what the others have said is right, it might even be far less dense, thus decreasing pressure. And as another plus it's closer too.

Cheers, Greg.

 

[Mirannan]

Psychotick - Air at one atmosphere in a vessel surrounded by virtually pure CO2 (which would be the case for an air balloon in Venus's atmosphere is almost as buoyant as hydrogen in Earth's atmosphere. The issue is the difference in density, which in turn is controlled by the average molecular mass of the gases concerned.

Earth's air has an average molecular mass of around 29 - slightly higher than that of pure nitrogen - and hydrogen of roughly 2 for a difference of 27. CO2 has a molecular mass of 46, so the difference between that and air is 19. Less buoyancy, sure - but not that much less. It would certainly work much better than a hot-air balloon does on Earth.

 

[Spiegal]

Hi Spiegal,

Not so sure about that. Air at one atmosphere isn't really that boyant. If it was we'd all be floating around instead of walking. And my understanding is that probes which have landed on Venus' surface (and lasted for all of a couple of minutes as I recall) have actually landed. Even at ninety atmospheres they didn't float.

However in my view it is easily more likely than Mars to be habitable - after some terraforming which would basically have to turn the organic content of the acid bath air into something inert. But it isn't hard to see that certain bacteria like life forms could be seeded in the upper atmosphere to do this job, and once the air is cleaned up the temperature would drop, hopefully to the point where you coul have liquid water, and if what the others have said is right, it might even be far less dense, thus decreasing pressure. And as another plus it's closer too.

Cheers, Greg.

Hi Psychotick, Mirannan put it better than I possibly could! The best analogy I can think of is an air bubble rising in water and comparing it to one rising in molasses. It's all relative to the medium it finds itself in. And yes quite right about the probes. The conditions they have to survive on the surface are incredible. The stress testing they put on the Venera landers were absolutely insane and they still only lasted a matter of minutes on the surface!

The whole terraforming idea would be technically feasible at some point I would imagine, it would take some extreme atmospheric engineering though. Bacteria would be a really interesting way of doing it, get some extremophiles to do the job for you

In the story they intended to keep the surface the way it was though, an endless supply of sulphuric acid to sell on the chemical market and get stinking rich from all the industries that needed it in such phenomenal quantities.

Sinister, have you considered how low gravity would affect processes like heat loss and digestion? In micro gravity you get a lot of trapped gas floating in the centre of your stomach rather than exiting your body. Similarly with no proper convection currents you get a nice blanket of hot air that stays close to your skin rather than dissipating in the air.

 

[psychotick]

Hi Guys,

Yeah I get that. However it still requires a balloon of some sort. Just filling a room with oxygen surely won't be enough to get it to float even on Venus. Consider the Earth equivalent a helium balloon. You can't just fill a room with helium and watch it float, yet that seems to be what Spiegal is suggesting.

As for the bacteria to terraform Venus atmosphere, you probably wouldn't even need extremophiles. After all the atmospheric temperature is going to plummet as you go higher. You'd need some sort of CO2 eating bacteria - i.e. a photosynthesising bug like a cyanobacteria, and it would need to have some acid resistence - pH 3 I think - though that would probably less of an issue at higher altitudes as well. Then you simply seed the atmosphere at the right height where temperature, pressure and acidity are tolerable and watch.

The bugs start growing and multiplying, fixing CO2 and if you've done it right, when they've fixed enough they get heavy and sink, taking the carbon down with them to the planetary surface. As time passes and the bugs work and multiply the atmosphere slowly adjusts, decreased carbon and lots of free oxygen.

With the CO2 decreasing two things happen. First the air density decreases because CO2 is a lot denser than oxygen / nitrogen. Second the temperature drops because a lot of the heat build up on Venus is due to a greenhouse type effect. And as these things happen the bacteria slowly sink to lower levels in the atmosphere where conditions are once again more favourable and the process continues.

The frightening thing is that I believe we have the technology to do that now. My only concern is that there might be some form of life - obviously not anything like us or based on our metabolism - which would be adversely affected / killed by the process.

Cheers, Greg.

 

[Spiegal]

Hi Guys,

Yeah I get that. However it still requires a balloon of some sort. Just filling a room with oxygen surely won't be enough to get it to float even on Venus. Consider the Earth equivalent a helium balloon. You can't just fill a room with helium and watch it float, yet that seems to be what Spiegal is suggesting.

As for the bacteria to terraform Venus atmosphere, you probably wouldn't even need extremophiles. After all the atmospheric temperature is going to plummet as you go higher. You'd need some sort of CO2 eating bacteria - i.e. a photosynthesising bug like a cyanobacteria, and it would need to have some acid resistence - pH 3 I think - though that would probably less of an issue at higher altitudes as well. Then you simply seed the atmosphere at the right height where temperature, pressure and acidity are tolerable and watch.

The bugs start growing and multiplying, fixing CO2 and if you've done it right, when they've fixed enough they get heavy and sink, taking the carbon down with them to the planetary surface. As time passes and the bugs work and multiply the atmosphere slowly adjusts, decreased carbon and lots of free oxygen.

With the CO2 decreasing two things happen. First the air density decreases because CO2 is a lot denser than oxygen / nitrogen. Second the temperature drops because a lot of the heat build up on Venus is due to a greenhouse type effect. And as these things happen the bacteria slowly sink to lower levels in the atmosphere where conditions are once again more favourable and the process continues.

The frightening thing is that I believe we have the technology to do that now. My only concern is that there might be some form of life - obviously not anything like us or based on our metabolism - which would be adversely affected / killed by the process.

Cheers, Greg.

Hi Greg, the quantity of atmospheric air would obviously have to counteract the weight of the structure in keeping with regular principles of flight weight<lift, but when the breathable atmosphere also doubles as a lifting gas it would require no external propulsion or bouyancy systems.

The dispersal of the bacteria to terraform is a really cool idea and no doubt there are some pretty likely candidates in nature as we speak. They would probably have to be in large cauldrons or implanted in some kind of permeable solid so they had some kind of a feedstock to metabolise with. I'm thinking of giant balloons carrying huge colonies of them reproducing and converting the atmosphere as they drift through the sky.

I personally prefer my Venus to be a nice duality, in the least earthlike environment it has the most earthlike conditions, and vice versa.

here is a report by Geoffrey Landis into the proposed habitation of Venus, he manages to make it sound like such an appealing place to live

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030022668_2003025525.pdf

 

[Mirannan]

The bigger the structure gets, the less important structural weight is. It's another consequence of the square-cube scaling law. Take two examples at the extremes just to illustrate the point: Aluminium sphere (density 2.7 - pulled out of the pile of rubbish at the back of my head ) of wall density 1cm, with a tiny air-filled void (1mm across) in the middle; its density is very little different from that of a solid block of metal.

Now consider an aluminium sphere of the same wall density but the whole thing is 1m across, so the void in the middle has a radius of 49cm. I think it's rather obvious that the density of this object is a lot less than that of solid aluminium, although I haven't calculated it.

Sure, I know this metal wouldn't be used - but I think the point is made.

BTW, the point about digestive gas in low or micro gravity is quite interesting. One of the things little talked about regarding life on ISS is that the place often smells quite a lot like a restroom, to use the American euphemism. The reason is that handling liquids and slushy solids (such as the food they eat) in microgravity incorporates large numbers of gas bubbles, which are then ingested.

 

[Spiegal]

Wow mirranan you really know your stuff, are you an engineer? I can see you being my go to person for this sort of thing!

It really is interesting to hear about the difficulties in the things we take for granted perhaps even more so than things like walking. When the kind of processes we never even notice going on become affected it really questions just how suited the human body is for space flight.

I was reading an article that also said how hard it was to talk with someone when their face is puffed up by the lack of gravity. Combined with the odd angles they would be floating at it could apparently interfere with the way the brain seeks out a face when you look at someone. It's a pretty cool psychological effect of low gravity environments that you wouldn't expect.

 

[Mirannan]

No, not an engineer Spiegal. Just a space enthusiast. I think you (and maybe others) might be amused - if it's on YouTube somewhere - by an old Mythbusters episode in which they took the expression "went like a lead balloon" literally. They ended up getting a lead balloon to fly. Very thin skin of lead, natch.

They had a lot of trouble with it, actually. The trouble is that lead is very dense and very weak - not a good combination for this purpose!