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Hi All
I wasn't satisfied with rough guessing what an atmosphere would do on Ceres, so I set up an iterative model from first principles and have some rough results.
Assumptions -
I haven't tried to model heat absorption, but might eventually.
mass: 9.5E+20 kg
rotation: 9.074 hours
equatorial radius: 483 km
Assumed constant Cp for the gas mixes - which is true (within a few %) for N2/O2, but CO2 changes a bit over the temperature range worth considering for humans. I used a rough average.
Rotation rate means Ceres effective gravity is zero at a radius of 1196 km on the equator. Things will be different for the poles. It's also assumed the atmosphere is rotating rigidly with the surface.
Results:
Po - surface pressure
P1 - pressure at synchronous altitude
To - surface temp
T1 - temp at synch
Do - surface air density
D1 - density at sync
Po P1 To T1 Do D1 Mass
1.01E+05 2.29E+03 2.88E+02 1.76E+02 1.22E+00 4.53E-02 8.60E+05
2.50E+04 3.79E+02 2.88E+02 1.76E+02 3.34E-01 8.28E-03 1.99E+05
2.50E+04 1.72E+02 2.88E+02 1.76E+02 3.97E-01 4.46E-03 1.79E+05
2.50E+04 8.85E+01 2.73E+02 1.48E+02 4.18E-01 2.73E-03 1.70E+05
Sorry it's not a proper table. The Mass column is the Mass (in kg) of the atmosphere (per sq. metre) up to the synchronous altitude. As you can see the atmosphere does rariefy quite substantially. More discussion later.
I'm quite fond of Rattus norvegicus having kept a few as pets - sadly they expired in a particularly nasty summer we had a few years ago in Australia. Rat studies are gainful employment for the little fellas and that particular study is fascinating - perhaps Martian-born colonists will happily handle what their parents couldn't without aid.
I've just completed a numerical model of different atmospheres on Ceres. I'll post some results in the Ceres topic.
An excellent mini-report there for us to ponder. Does make the situation somewhat happier than we were led to believe - and I've no doubt that medical technology could improve matters if we were willing to push the boundaries even further. Consider the bicarbonate handling abilities of crocodilians, for example.
Good point too about partial pressures versus percentages. I think a similar misunderstanding confuses people about oxygen levels and flammability.
So could our Martian colonists adapt to a 50:50 mix of CO2/O2 at 240 mbar? I would tentatively say "yes", so long as it wasn't excessively cold. What's the main cause of the "Death Zone" that mountaineers face when scaling Everest? Low pressure, low O2 or cold conditions? Didn't Tim McCartney Snape scale Everest without supplemental O2?
Hi Gregori
Terraforming neptune is hopeless. Its not an earth like enviroment and no matter how much time and energy you wated on it, It will never become one.
We could however adapt to living in its upper atmosphere using clever technology and engineering. Bacteria that are independant of sunlight for energy may be a possible food source, that or plants grown indoors under artificial light.
I reckon that Fusion power is the key technology to make this all possible.
You're probably right, but I guess my definition of "terraform" is to create an open-air habitat for terran life - or come as close to that as you can. If that means balloon-borne habitats on a landless planet, that's pretty good if the air is breathable.
Terraforming Ice & Gas Giants is an ultra-tech prospect, not anything like Mars or the Moon. But it's an interesting speculation, if only for planetological reasons.
Hi Mansouryar
Your wormhole work is interesting and - in another forum, where the reaction was unreasonable scepticism - you've asked what the implications of wormholes might be. I'd like to put a few thoughts out there.
Firstly, the impact of wormholes will depend on the necessary technology and power-levels. If they're easy to generate and maintain, then the impact will be incredible - I'll elaborate in a moment. If they require lots of energy and are difficult to keep open, then their uses will be much more limited until the energy problem is solved.
Secondly, if wormholes are restricted to being made and connected locally, then moved around at sub-light, they will be useful short-cuts, but the wave-front of human endeavour will expand at sub-light. If wormholes can be projected, or moved via warp-metrics, at FTL speeds then that situation changes totally.
But let's look at the possible uses, starting with direct travel.
To ship a wormhole, assuming it's low-mass, we can attach a rocket to its cage and fire it off - just about any rocket will do, then we can pipe propellant to it via the wormhole. To push a wormhole/rocket combination weighing 1 ton to near lightspeed would take ~ 100,000 tons of propellant - assuming we're using a steam rocket with 3 km/s exhaust velocity. That water is a lake a hectare in area and ten metres deep. A cubic kilometre of water lets us move ~ 10,000 tons, or 10,000 wormholes. That's enough wormholes for roughly every star within ~ 94 light-years, which would be reached in ~ 127 years at the latest. In about ~ 110,000 years every star in the Galaxy could be linked up via wormhole. Using merely Earth's water - which we wouldn't - the job would be done with just ~ 0.74% of the total.
Assuming a 10 gee rocket we could send a wormhole to Pluto in ~ 5 days. If wormhole maintenance costs are low enough, then we could profitably ship frozen nitrogen and methane from its surface. We could mine hydrogen clathrate from Sedna or some other Inner Oort Cloud object. Or suspend a wormhole mouth via a balloon and funnel hydrogen/helium direct from the Jovians, petrochemicals from Titan's lakes, raw sunlight from Mercury, or - assuming advanced reflective materials - pipe intense sunlight straight from the photosphere of the Sun.
Assuming a wormhole stable against the conditions we could send them into the core of the Sun to cause mixing between the Core and the outer layers, thus increasing the Sun's remaining lifespan 10-fold. The process would take ~ millions of years because the inner regions are very dense, but we're talking billions of years anyway.
The transport implications are complex because we have so few parameters on what wormholes will be possible - there's questions of conservation of momentum and energy when transferring between different points on the Earth or in-space: Will masses moved between planets keep the momentum they had relative to their original position? Does an equal amount of mass need to pass both ways to keep the balance?
Imagine wormholes at different heights in a gravity well - say a mass falls into the lower wormhole then emerges from the upper wormhole aimed at the lower again - would the mass keep gaining energy indefinitely, looping through the holes to ridiculous speeds? Would that drain energy from the wormholes instead? Do you have answers to these questions Mansouryar?
The other option was fusion pulse using fusion ignitors using high-energy density materials - like hi-energy nitrogen, which has recently been produced in a lab. Such solid nitrogen might have enough omph to be a totally non-fission fusion trigger for an Orion-style launcher.
Hi All
GCNRevenger wrote:
"As far as I know little work on the GCNR concept has been carried out since the ideas' invention beyond some pre-computer table-top fluid dynamics models and some low-definition physics studies. Nobody has picked it up with intent to actually build the thing yet to my knowledge. "
The Russians worked hard on GCNRs...
http://www.astronautix.com/engines/rd600.htm
...but the Americans abandoned their Mars program in 1970 and the Soviet leadership lost all interest.
Hi All
For the record, wormholes don't allow FTL.
Technically, no. But FTL isn't out of the question in GR so long as lightspeed isn't violated locally. So when travelling through a wormhole from A-to-B you don't go FTL at any point along the way, but a distant observer will see things quite differently.
Where are you going to get enough Xenon from?
I'm really dubious about the claim that the Moon's atmosphere would escape in just a few centuries - that just doesn't seem right. How? One atmosphere pressure on the Moon would need an air column mass of ~ 62,500 kg/sq.metre - if all the sunlight hitting the Moon went into launch the air into space some 16 years worth would be needed at 100% efficiency - which wouldn't happen. To happen in just 200 years would need 8% efficiency of energy-into-atmosphere - which also seems a tall ask. Earth's mesosphere doesn't absorb that much energy, no way, so I very much doubt the Moon's would.
Another issue is water loss. Dehydrating the Moon takes energy - lots of energy. Busting apart hydrogen from water (H2O -> H + OH) takes 15.63 MJ/kg - a 1,000 metres of water on the surface would need 1,450 years of all the Sun's energy that hits the Moon to just dissociate. But since the high energy end of the solar spectrum is needed (just 6% of the total) that time extends to >24,000 years at 100% efficiency. The stratospheric cold trap would work as well on the Moon as on Earth - if not better - so the actual loss time would be much higher.
Hi Guys
Unshielded habitats! In deep space! What person would live in those? You'd be dead pretty quickly of radiation sickness. Unless you dosed up on antiradiation drugs, that is.
For galactic cosmic rays, only very thick layers of shielding weighing tonnes per square metre will give full protection. Cosmic radiation will give doses of 30rems per year to unshielded personel in free space, but the dose will be spread over the whole 365 days. A healthy diet full of antioxidants will counteract most of the damage.
One advantage of a bag colony - a few kilometres of air stops GCRs dead (turns them into muon showers.) Are muons sufficiently like beta-rays to be innocuous, or are they more penetrating? They contribute to ~50% of our normal dose of rads though, so our bodies are adapted to them.
GCR damage isn't something easly repaired by the body. They kill non-regenerating cerebral neurones directly - and so GCR damage would progress like Alzheimer's disease with its gradual decline into full dementia. Regular radiation is just in the MeV range, so the body can fix it easily - but +GeV energies leave a track through the body of damage that's hard to fix.
Personally I think John Slough's Plasma Magnet might be the best GCR shielding option. And its mass-density requirements are much lower than a basalt shield. But a few metres of asteroid regolith does the job just as well - thus my preference for digging in on an actual body in space.
Oh, so this isn't something that could get us to mars, or even the moon?
If you want to accelerate very slowly it will get you to the Moon - though Mars would need too much propellant.
Radioisotopes are rather nasty to handle in any great quantity - they usually have low critical masses and so can't be made into a high-power nuclear core as a result. That and being red-hot all the time.
Better with a metal-oxide fission reactor using uranium - according to Scott Howe the release of fission products can be all but eliminate making the exhaust stream essentially non-radioactive. Problem is that the old style NERVA design is under-powered and has a narrow thrust range. A better NTR design is the DUMBO system, which you can look up as it has recently been declassified and is available on the Web.
BUT there is another option...
Hi Guys
I think the distinction between terraformed, orbiformed and artificial worlds is pointless. Arguing for one or the other is stupid because neither has been achieved yet. The first habitats will be on natural bodies, but if we're talking asteroids they won't stay "natural" for long, as the whole thing is either mined or converted. I've often wondered just what O'Neill style Free-Space colonies were supposed to live off in terms of natural resources - which they don't have. Why is an L4 colony preferable to a Moon City? Or a multi-level converted asteroid? Our gravity-prejudiced preferences focus on big, flat living spaces, and that's what O'Neill wanted to dangle as a carrot to the human race, but his was a Utopian dream with no idea what real "life in space" would mean.
So I tend to remain very sceptical of the whole O'Neill thing, as much as I loved the art-work and romantic idealism when I was a kid. Now it just seems like - literally - castles in the air. If people choose to live in low gravity then they'll find ways around its deletrious effects and the idea of rotating cylinders and spheres full of empty air will just seem silly and wasteful.
At the same time I suspect there will be an urge to shame other celestial bodies to something more like Earth, and efforts to do so on a mass-scale. Whether it's via orbiforming, World-Houses or terraforming is not ours to decide here and now. We're trying to delineate the possible not set-in-stone what's desirable.
As for Ceres, physics is telling us that a gravity-constrained atmosphere isn't possible. I don't believe the magnetic field thing will work either, but my magnetic theory skills are pretty weak. I suspect the required fields would be intense and unlikely to be produced on a planetary scale. Maybe someone will invent a Jack Williamson-style "paragravity generator" to terraform asteroids, but for now only shells, domes and tunnels will work to keep air in - on whatever scale the Belters desire.
Ceres equatorial illumination levels are 0.075kwh/m2/day. That is comparable to winter illumination levels in England. Crops will grow under those conditions if provided with adequate water and optimum temperatures. But growth is generally retarded by lack of light. Further from the sun than Ceres and sunlight becomes too weak to be of great value.
Perhaps, though I would still like to see hard data.
Even at Ceres distance, the productivity of the ecosystem would be low and would become zero abovce a certain latitude. So the holding capacity of Ceres would be much smaller than an equivelant amount of land on Earth, or even on Mars. Yet the difficulty of terraforming ceres might be an order of magnitude higher.
What do you think of improving plant efficiency? Another thought I had was the attenuated light levels parallel the low light of the lower levels in a gallery forest.
I realised today that a roofed world would be exceptionally vulnerable to impacts. A large explosion on the surface, would send shockwaves through the atmosphere, ripping off the iron roof hundreds of kilometres from the impact site. So a roofed world house isn't really a sensible option. This would also be a problem for sealed O'Neill type colonies. As a metoer passes through the outer shell, it would compress the air within the habitat and fracture the hull. Rather like a bullet passing through an apple, the meteor would not leave a neat hole.
O'Neill colonies and roofed Worlds would need active defense systems, like automatic lasers and/or kinetic interceptors (rapid-fire rail-guns, which don't yet exist.) But also a multi-layer Whipple shield of nanotube fibre would stop most impactors.
Hi Antius
I'd like to see hard data on growth in low light before I have a real opinion on the "not enough sunlight for growth" claim you make. Plants with plenty of sunlight often have a hard time using it because of evaporation and over-heating. And how much of the Sun's incoming energy do they actually use? Perhaps in low light they can be tweaked for higher efficiency. That's my particular take on this matter.
But to illumine Ceres wouldn't take a vast soletta anyway, so I think the difficulty is more imagined than real. Consider a transparent shell at synchronous altitude (lowest stress position for it IMO) - the shell also acts as a light collector through tricky surface coatings and bounces incoming light towards the surface. Easy. If we can make a transparent shell 2400 km wide then we can do the optics too.
Problem is: what sort of bursting strength do we need to keep the air in?
Hi Karov
Gases exerting a pressure need a counter-force so they don't expand away into space...
For Ceres -- even sprinkling away atmosphere via axial rotation -- what would be the gas pressure of the 'surface' of gas bubble with radius of 10 000 km? around Ceres ( or whatever )? I expect the ambient pressure to not be higher than the Earth one at several hindred kilometers hight... hence pretty modest power needs to keep the air around.
...the problem is that 714 km up there's no effective gravity on the gas anymore. Nothing to provide a counter-force to its free expansion into the void. Simple fact of physics is that gas at any reasonable temperature has too much internal energy to be kept against Ceres by gravity alone. Only an Air-Shell will keep the pressure on the surface.
Look at it this way. What's the gravitational potential of Ceres at its surface? Just 133,450 J/kg. Earth is 62.5 MJ/kg and the Moon is 2.8 MJ/kg. The internal energy of air at 288.15 K is 291,800 J/kg - much less than the potential of the Moon or the Earth, but more so than Ceres. That air has enough energy to leap into space.
Of course as it expands the stuff does work against itself and it cools down. But, at the same time, it's absorbing heat from the Sun, so maybe it doesn't cool down very much at all. Thus why I assumed an isothermal atmosphere originally. And my point is that air at reasonable temperatures has enough energy to easily escape Ceres. The gravity of Ceres isn't enough to attenuate the gas at the altitude we want a plasma "shell" to operate.
I was talking about adding mass to Juipiter, not Venus.
That was a few posts back. I think I got lost. We were talking about Venus as well as Neptune etc...
But there's not enough mass in the Oort Cloud or the Kuiper Belt to make Jupiter a brown dwarf, by the usual definition i.e. deuterium burning mass of 13 Jupiters. Turning Jupiter into a brown dwarf isn't such a "hot" idea with the Galileans so close by.
Problem with Jupiter, and to a lesser extent Neptune, is too much hydrogen for comfort. On Neptune we might be able to do something about it via turning hydrogen into carbon/oxygen and making a diamondoid/carbonia shell for a seafloor. Jupiter, however, is too damned hot and too dry. Perhaps it can be cooled, or perhaps we should kindle its fires and make it into a real star.
Of course any big ocean planet faces the problem of the ocean freezing when it gets cool enough. At about a million bars water probably turns into ice XII or some other high-temperature polytrope, somewhere over 2500 K or so.
Hi All
Anyone know how to work out the atmospheres height?
Atmospheric pressure and density fall-off exponentially - for every increment of what's called the scale height the pressure/density decrease by a factor of e (=2.71828...) The scale height is height(z) at which the gravitational potential (with respect to the surface) equals the average molecular energy (kT) of the gas:
mgz = k.T
...BUT that's the non-varying surface gravity approximation. To work it out for small planets you have to use the gravitational potential in a radial force field. Sounds imposing but it's just V = GM/R, where G is Newton's constant, M is the planet mass, R is the radial distance. After a bit of fiddling I get:
mgzR/R(s) = kT
...where R is the radius of height z, g the surface gravity, R(s) the surface radius. Plugging in the numbers for Ceres (Earth normal gas, T= 288.15 K, m = 28.96, g= 0.27 m/s^2) we get z = 304 km. But the gravitational potential doesn't decline linearly with radius anymore. To work out how much the pressure declines for an isothermal atmosphere we get:
P = P(0).e^-(z/z(0)) (non-radial case)
P = P(0).e^-(z/z(0)).(R(0)/R) (radial case)
...as you can see the radial gravitational field's pressure declines slower because it's reduced by the R(0)/R factor (R(0) being the first scale height's radius, R being the altitude we want the pressure at.) So for Ceres at an altitude of 714 km, the pressure has dropped to 38.8% of its surface value (Ceres radius 483 km)...
Except we didn't take the rotation of Ceres into account and at 714 km altitude is the synchronous orbital altitude - any gases feel effectively zero gee. Beyond that altitude and the gases feel a net acceleration away from Ceres. Thus my reason for calling Ceres' atmosphere a gigantic sprinkler flinging gas into space. I'm not sure how strong a magnetic field would hold that in either.
So, if we're aiming for a 650 millibar atmosphere, 250 mb of Oxygen, 50 mb of CO2 (don't know whether humans can survive that, probably has to be lowered), and the rest Supergreenhouse gasses?
A partial pressure of 50 mb CO2 is about the maximum tolerable, and even then a lot of people would feel shortness of breath, headaches and so on. Super-greenhouse gases don't need to be present in such great numbers - microbars usually will do. A surface pressure of just 300 mb total is probably fine so long as it's not too cold.
Hi midoshi
Of course the stuff is toxic, but my main idea was for rocket exhausts to add atmosphere to the Moon. Eventually we'd learn how to make oxygen out of the rocks and/or wring water out of the deep mantle, but for a temporary atmosphere that would stick around SO2 seemed a good idea.
Hi Terraformer
I don't want to breathe SO2 but it's available, and it'll be a pollutant from rockets using indigenous fuels - the other options being powdered aluminium or iron in LOX. It might be useful for an initial atmosphere until we work out an easier way of cracking oxygen out of the rocks.
Sulpher Dioxide?!?! I thought we were talking atmospheres for breahing, not just braking. You really want to be breathing that in?
I didn't think there was much potassium in the Moon for argon to be belched by lunar vulcanism.
Argon? It makes up most of the present atmosphere and is being constantly replenished by the internal workings of the moon.
Of course Stephen Baxter (and Poul Anderson before him) could be right and there's lots of water-of-hydration in the deep mantle. Perhaps we can get the Moon to belch it up, along with assorted gases like SO2, N2 perhaps. Current "Big Splat" simulations don't have enough resolution to say whether the Moon formed purely out of rock vapour or out of intact mantle chunks, so there's a chance there's water down there.
Hi All
According to Jim Kasting's models CO2 starts turning into ice clouds at about 0.5 Earth insolation levels, and at 0.36 Earth insolation the cloud cover becomes total. No further pure CO2 greenhouse is possible, so the atmosphere would need super-greenhouse gases like ammonia, methane and fluorocarbons.
Hacking a bit at the C02 math.
Ceres being a mean temperature of -100°C.
With 1 bar of C02 at Ceres adding around 70c, we end up with a world somewhere around -30c.A mix of super greenhouse gasses or methane in the atmosphere and it's not beyond the realm of being a world above 0c.
By themselves CO2 ice clouds are brilliant IR scatterers BUT the surface is potentially very dark as the ice crystals are big - look at the recent views of CO2 ice cloud shading on the surface of Mars seen by Mars Express.
As we get further out in the solar system the numbers become more dismal for C02.
Moons around Jupiter will require 2 or 3 bars of C02 to have a hope of being a 0c place.
Around Saturn more like 10 bars of C02.
As I said the modelling indicates we'd need to be using methane and ammonia. Jonathan Lunine and Ralph Lorenz modelled Titan's atmosphere under a ~ 5 bar (!) CH4 atmosphere and only got a 50 C rise out of it because of the counteracting effect of tholin haze production. If the Sun was cooler - or we put a big filter in place - the tholin problem would go away and the surface temperature would go way up. Modelling of a haze free Titan atmosphere in the 1970s got the surface temperature up to 155 K in a 0.5 bar CH4/H2 atmosphere. In the late 1970s there was thermal data suggesting a 200 K surface temperature on Titan, which needed a 21 bar nitrogen atmosphere to be possible. Based on ammonia levels in the ices that should be possible to generate.
My guess as a minimum bearable temperature for humans is around -70c since Eskimo's go indoors at those temperatures.
We could probable add another -30c to that with heated suits, that puts us at around -100 as a minimum bearable temperature for both men and machines on a moon or planet surface.
There's a Siberian town which gets down to ~ -60 C or so during winter, so I don't doubt the temperature you quote. Earth's lowest ever is ~ -87 C, at altitude on an Antarctic mountain, so the heavy N2 atmosphere of Titan would be about right.
Hi Terraformer
Dropping cometoids from 100 AU out takes a minimum 176.8 years via gravity alone. Going out to 1,000 AU and the waiting time is 5,600 years. Getting them to Venus quicker would consume more reaction mass, perhaps too much.
Hi Antius
Thanks for the reply, but I have a few issues with the idea applied to small worlds like Ceres.
Firstly the column mass for Ceres' 0.028 g is HUGE and the scale-height, adjusted for small planetary radius, is larger than its physical radius - it would still be quite dense at the synchronous orbital altitude of 720 km, thus Ceres would fling its atmosphere into space like a huge sprinkler. Assuming Earth-like temperatures and pressures at the surface, of course.
Secondly, the column depth means the atmosphere would attenuate sunlight incredibly - even more than sunlight is attenuated at sunset, for example. I'm not sure what that would do for habitability, but it wouldn't be good.
Thirdly, just how does the magnetic trapping work? We're talking about magnetically trapping ions at the top of the atmosphere? Make them fast enough and they would hold atmosphere in just like a plasma window keeps air out of a vacuum chamber, but that's one heck of a "plasma window"!
Hi All
Hydrogen and methane are both greenhouse gases and above a certain mixing ratio they're non-flammable when oxygen is around - though we're talking 10 bar pressure for the mix to be breathable.
Hi All
Since there's negligible xenon around for making atmospheres let's use sulphur dioxide since we know there's both elements on the Moon, and it would be a "natural" pollutant from using Brimstone+LOX rockets. Its molecular mass is 64, which is better than oxygen, and it freezes at 200 K so it might be effectively "cold trapped" at night.
Hi Terraformer
The Solar Wind is typically about 5 protons per cc and travelling at ~ 300 km/s. That means the Sun is throwing out about ~ 4.2 E+35 protons a second, or just 710,000 tons of hydrogen a second. About 22.3 trillion tons a year - sounds like heaps, but Venus needs about 1,976 years worth of Solar Wind hydrogen (all of it) to turn its carbon dioxide into water and soot. Quicker to look for the stuff elsewhere.