Can a small body be given an atmosphere?

RickSmith · 2007-04-15 20:18:10

... but I think with sich magnetic atmosphere confinement, really LITTLE bodies could be centered in magnetic atmospheric sacks / bubbles / confinement. I wonder what`s the lowest limit for the central mass , if any. EM is trillions and trillions asnd trillions times better interacting weith our matter than gravity, so with locally abundant energy resources, the job seems to be possible -- solar EM radiation and solar particle wind must give enough power to hold human grade atmosphere around smaller objects...

Hi all,
From time to time Karov posts his idea (of using an artifical magnesphere to allow tiny bodies to keep an atmosphere) in posts on other topics. This thread is intended to be a place where this idea can be discussed.

He is perfectly correct that electro-magnetic forces are many times more powerful than gravity (10 E 36 times more powerful ! ). So the raw umph is certainly there to keep an atmosphere. The main problem is that while gravity works on everything the electromagnetic force only works on charges.

Plasmas are STRONGLY confined by a magnetic field. However neutral atoms ignore them. Unless I am misunderstanding something, the neutral atoms will leak thru his shield like it is not there.

Karov, would you care to comment?

Warm regards, Rick.

noosfractal · 2007-04-15 23:49:13

The outer layers of the atmosphere would have to be an ionosphere and then plasmasphere. Happily this seems to be the natural order of things in the presence of the Sun's ionizing radiation. Outer solar system atmospheres may need an ionizing radiation boost.

RickSmith · 2007-04-16 00:27:04

Are all atoms in the ionosphere ionized?

Even assuming that all of them are, In a magnetic field the electrons will spiral towards one way and the positive charges will go the other. If an electron hits a positive ion (and sticks) they will become a neutral atom on a ballistic course.

My gut feeling is that this shield will leak unless it has something else going for it.

Warm regards, Rick.

noosfractal · 2007-04-16 01:59:11

The magnetosphere will definitely leak, the relevant question is: how much? The name of the game is reducing the ratio of escape velocity to average particle speed in the upper atmosphere as explained here ...

http://cseligman.com/text/planets/retention.htm

and in particular in the section titled ...

Summary of How Particle Velocities Compare to Escape Velocity

A magnetosphere protects the upper atmosphere from being heated by the solar wind, and consistently modifies the particle orbits back towards the inside of the sphere (effectively raising escape velocity). It doesn't have to keep every particle, just reduce the ratio of particles that reach escape velocity.

Compare Earth (magnetosphere), Mars (minimal), Venus (minimal). Earth has most (but not all) of its atmosphere from 1 billion years ago, whereas Mars has lost most of its atmosphere, and Venus has lost most of its lighter elements.

RickSmith · 2007-04-16 02:07:27

The magnetosphere will definitely leak, the relevant question is: how much?....

Ok, thanks.

I thought Korov was saying that basically any small body could be given an atmosphere with this technique.

Warm regards, Rick.

noosfractal · 2007-04-16 02:14:47

I thought Korov was saying that basically any small body could be given an atmosphere with this technique.

Maybe. Depends on how high a strong magnetosphere can raise the effective escape velocity.

BTW, check out this shockwave atmospheric retention simulator ...

http://astro.unl.edu/naap/atmosphere/an … ulator.swf

You lose all your hydrogen in nothing flat

Tom Kalbfus · 2007-04-17 08:21:46

Seems to me, what you want is a roundish asteroid, about 10 miles in diameter, then surround that with an airtight clear plastic envelope, and inflate it with air so that its 100 miles in diameter. Place an airlock at one end and another airlock at the opposite end. The gravity of the asteroid should keep it centered on the inside of this gas bag. 45 miles of atmosphere at mostly 1 bar should be enough to screen out most of the harmful radation from the sun, and should screen out the comsic rays.

The gas bag when not full of air has an opening in it, when it is brought over to the asteroid folded up. You unfold the gas bag and the opening is big enough to slide over the asteroid and completely engulf it. After you've baged the asteroid, you seal that opening, install the two airlocks, and you inflate it with a breathable mixture of gases, add some water and you've "terraformed" the asteroid. add some soil and you can grow plants on the asteroid's surface. I think trees might grow without bound in this microgravity environment and would have to be trimmed to avoid puncturing the gas bag. So what do you think of this idea? Doesn't require huge magnetic fields.

karov · 2007-04-30 06:06:14

Given mechanical erosion protection ( solar wind, impacts ), the only thing relevant before the successfull atmosphere retention would be the RATIO: escape velocity VS. thermal velocity at the exobase. We know that if the particles` velocity in the exobase is kept under 20% of the escape velocity in the exobase, than an atmosphere could persist billions and billions of years, i.e. the same time order as the normal geological and astrodynamical lifespan of a planet, i.e. indeffintelly long, i.e. practically "forever". For smaller bodies that means REALLY cryogenic tempeatures necessary. Once, I calculated for 3-5% gees body Pluto as far as I remember, similar for Vesta, Juno, Ceres... and the results were that for nitrogen and oxigen 30-40k sufficed. Even sub-1k cryo-cooling is feasible I think.
Many proposed laser cooling, but much more appropriate would be kinda |plasma coolin`| -- i.e. version of the Peltier-Zeebeck effect working in fluid charged medium.

The Non-charged component of the high atmosphere of the little body could be charged via channeling to meet the ficused solar wind, via collisions with the decelerated cooled charged ones, etc.

G.K.

Antius · 2007-05-22 06:33:25

A fascinating idea, one that has appeared several times before on this list, if memory serves. If I understand it correctly, the idea is to provide a minor planet/moon with an atmosphere. The sun will ionise the upper layers of the atmosphere, which will gradually escape into space, given that the average speed of the particles is greater than escape velocity. By giving the world a magnetic field, the ions are caught before they can escape and will basically spiral along the field lines, reentering the atmosphere at the poles.

It could work, but is loaded with problems. The first problem, is one of economics. Firstly, in order to provide Earth surface pressure on a world like Ceres, the planetoid would need to have something like 30% of the Earth's atmosphere. That's an awful lot of gas - equivelent in mass to a full 1% of the mass of Ceres. The easiest way to create such an atmosphere would be to trap a comet in high orbit about the planetoid. The sun would gradually vapourise and ionise the comet and the ions would be trapped within the magnetic field, gradually building up an oxygen/water vapour atmosphere (the H2 would escape into space).

The good thing about an atmosphere that deep is that it would trap IR radiation very efficiently, keeping the surfcae warm even at great distances from the sun. The bad thing is, it may not be transparent to the visible part of the spectrum, which is obviously important for plant growth.

For most candidate planetoids/moons, the surface must not be allowed to rise above zero, given that most outer solar system worlds are covered in ice to a depth of at least a few hundred kilometres. This may make an active ecosystem or comfortable environment difficult to maintain. Also, the sun is too dim beyond Jupiters orbit to allow significant plant growth without artificial light.

At the end of the day, i am left wondering why any future society would bother going to so much effort to create what is sure to be a cold and miserable little planet. Far more promissing to concentrate efforts on free space habitats, which have completely controllable internal environmental conditions and geography.

Antius · 2007-05-22 06:41:26

Given mechanical erosion protection ( solar wind, impacts ), the only thing relevant before the successfull atmosphere retention would be the RATIO: escape velocity VS. thermal velocity at the exobase. We know that if the particles` velocity in the exobase is kept under 20% of the escape velocity in the exobase, than an atmosphere could persist billions and billions of years, i.e. the same time order as the normal geological and astrodynamical lifespan of a planet, i.e. indeffintelly long, i.e. practically "forever". For smaller bodies that means REALLY cryogenic tempeatures necessary. Once, I calculated for 3-5% gees body Pluto as far as I remember, similar for Vesta, Juno, Ceres... and the results were that for nitrogen and oxigen 30-40k sufficed. Even sub-1k cryo-cooling is feasible I think.
Many proposed laser cooling, but much more appropriate would be kinda |plasma coolin`| -- i.e. version of the Peltier-Zeebeck effect working in fluid charged medium.
The Non-charged component of the high atmosphere of the little body could be charged via channeling to meet the ficused solar wind, via collisions with the decelerated cooled charged ones, etc.
G.K.

30-50K is more than the average surface temperature of a body at Pluto's distance from the sun, so it would probably work. Much cooler than that and you need to go lower than natural background radiation will permit as far as i can see. Below about 20K is impossible without surrounding the world with some sort of physical barrier that blocked out incoming radiation.

Again, the question in my mind is: what is the point? Why not simply mine materials from such a body and use them to produce a bernal-sphere type free space colony, in which you have complete control over internal conditions and can tailor them as you desire? Why would we choose to colonise a body whose surfcae is nothing more than worthless ice?

Maybe there is a point that i have missed. In any event, the sirfcae would need to remain below zero to prevent it from melting into a global ocean.

noosfractal · 2007-05-23 22:44:31

Hi Antius, welcome to newmars.

I think the main reason for considering putting atmospheres around small bodies is long term stability.

I'm a fan of O'Neill cylinders but they have an inherent instability: a high pressure (i.e., 1 bar) atmosphere separated from vacuum by a relatively thin skin. I have no doubt we can engineer systems that cope with this instability in the vast majority of circumstances, but eventually the cylinder will encounter the astronomical equivalent of the hundred year wave. Even if the design can be made immune to natural menaces, the instability is there to be exploited by malicious actors (internal and external). The necessary docking ports are at least cumbersome, if not a point of special vulnerability.

If the magnetic field around an atmosphered small body is disabled, the atmosphere will eventually be lost, but your time to repair can probably be measured in years rather than hours. Also, atmospheric entry shouldn't be a huge issue in low gravity environments, particularly since aerobraking can be a big fuel saver, because then any mods required for atmospheric entry can be justified by fuel savings.

Some notes w.r.t. your other points:

- see the "Moving Ammonia Asteroids" section of Zubrin's _Technological Requirements for Terraforming Mars_
http://www.users.globalnet.co.uk/~mfogg/zubrin.htm
for an idea of economically bringing volatiles to small bodies

- if we can engineer the other stuff, I'm sure we can engineer an atmosphere transparent in the important regions for plants, however, as you say the sunlight may be too faint in any case, in which case we may first want to use the small bodies' own volatiles to change it's orbit to something more viable

- an ocean world with artificial islands is not an unappealing habitat. Everyone gets beachfront

Antius · 2007-05-25 02:07:09

Hi Antius, welcome to newmars.
I think the main reason for considering putting atmospheres around small bodies is long term stability.
I'm a fan of O'Neill cylinders but they have an inherent instability: a high pressure (i.e., 1 bar) atmosphere separated from vacuum by a relatively thin skin. I have no doubt we can engineer systems that cope with this instability in the vast majority of circumstances, but eventually the cylinder will encounter the astronomical equivalent of the hundred year wave. Even if the design can be made immune to natural menaces, the instability is there to be exploited by malicious actors (internal and external). The necessary docking ports are at least cumbersome, if not a point of special vulnerability.
If the magnetic field around an atmosphered small body is disabled, the atmosphere will eventually be lost, but your time to repair can probably be measured in years rather than hours. Also, atmospheric entry shouldn't be a huge issue in low gravity environments, particularly since aerobraking can be a big fuel saver, because then any mods required for atmospheric entry can be justified by fuel savings.
Some notes w.r.t. your other points:
- see the "Moving Ammonia Asteroids" section of Zubrin's _Technological Requirements for Terraforming Mars_
http://www.users.globalnet.co.uk/~mfogg/zubrin.htm
for an idea of economically bringing volatiles to small bodies
- if we can engineer the other stuff, I'm sure we can engineer an atmosphere transparent in the important regions for plants, however, as you say the sunlight may be too faint in any case, in which case we may first want to use the small bodies' own volatiles to change it's orbit to something more viable
- an ocean world with artificial islands is not an unappealing habitat. Everyone gets beachfront

I'm highly sceptical. Firstly, if we are talking about heating an icy world to earth surface temperatures and melting it into a global ocean, where will the inhabitants get their mineral resources from? It would appear that they would sink to the bottom of a global ocean 100's of KM deep in mnay cases. Also, whatabout soil for growing crops? The only other alternative would be to cover the icy surfcae in an artificial (metal?) crust, before heating takes place. But then you run into the problem of what happens if the crust is pierced by a meteorite. This is also planetary engineering on a ridiculous scale.

Second, for most bodies, artificial lighting and artificial power would be a neccesity simply to grow food and keep the place warm enough for survival. This would appear to make the ecosystem just as vulnerable to catastrauphic disruption as any orbital habitat. A large meteorite hit would be just as catastrophic for a world like this as it would be for a space colony.

The other alternative would be to heavily insulate individual areas of the icy surface, dome them off and heat them, building our cities and cropland on the heavily insulated surface. This would allow the planets average temperature to remain below zero, but reach comfortable temperatures in particular locations. But again, it is difficult to justify the massive cost of paraterraforming such a barren world, for such a limited amount of holding capacity.

noosfractal · 2007-05-25 03:47:59

I'm highly skeptical.

A very profitable attitude to take. I’ll play devil’s advocate.

Firstly, if we are talking about heating an icy world to earth surface temperatures and melting it into a global ocean, where will the inhabitants get their mineral resources from?

The lowest bidder? I don’t see them being at an economic disadvantage compared to completely manufactured thin-shell habitats. If a thin-shell habitat can economically disassemble an asteroid for materials, then so can aquaoid. I think artificial island manufacturing costs will be lower.

It would appear that they would sink to the bottom of a global ocean 100's of KM deep in many cases.

But isn’t this an improvement over the minerals being under 100s of kilometers of ice?

Also, whatabout soil for growing crops?

Is soil required for growing crops? There was a hydroponics movement at one point. If soil is required, then it can be imported from C-type asteroids, same as for thin-shell habitats.

The only other alternative would be to cover the icy surface in an artificial (metal?) crust, before heating takes place.

I think artificial islands would be sufficient. Tethered to the core if necessary.

Second, for most bodies, artificial lighting and artificial power would be a neccesity simply to grow food and keep the place warm enough for survival.

I think you mentioned that the deep atmosphere would help keeping the asteroid warm – especially if it were enhanced with super-greenhouse gases. For a given solar input, I think this gives the advantage to the aerolith.

Light for crops is a huge issue for both scenarios. Plants are very inefficient users of solar energy, and I have no idea how efficient they can be made. I can imagine a fungi or algae based food system. Sea food seems a natural for aquaoids.

An idea for delivering solar energy to trans-Jupiter aeroliths is a series of large (100 km radius) Fresnel lenses. The first one close in to gather the energy, others in the series to refocus the beam until it reaches it’s destination. This paper ( see http://www.llnl.gov/tid/lof/documents/pdf/241039.pdf ) describes gossamer lenses made of solar sail type material, but we might be able to use even lower mass plasma rings.

This would appear to make the ecosystem just as vulnerable to catastrauphic disruption as any orbital habitat. A large meteorite hit would be just as catastrophic for a world like this as it would be for a space colony.

Actually, I don’t think large meteorites are the main threat. If they are big enough you’ll spot them and divert them in time. Perhaps the bigger threat is a swarm of smaller meteorites that overwhelms the thin-shell habitat’s defense and/or repair systems, or maybe a huge burst of gamma radiation from a nearby supernova. The aerolith has the advantage in both these cases. You’ve also ignored deliberate attacks by people, which might be the biggest threat of all.

The other alternative would be to heavily insulate individual areas of the icy surface, dome them off and heat them, building our cities and cropland on the heavily insulated surface. This would allow the planets average temperature to remain below zero, but reach comfortable temperatures in particular locations. But again, it is difficult to justify the massive cost of paraterraforming such a barren world, for such a limited amount of holding capacity.

Even if you prefer an ice worldlet instead of a water worldlet (perhaps we could just leave the poles frozen for those who have some special phobia of artificial islands) your construction costs are going to be lower for just insulation vs. insulation and pressure.

Artificial island in atmosphere vs. artificial island in vacuum. The atmosphere costs more at first, but it may be a good long term investment.

nickname · 2007-05-25 07:41:38

This is not directed towards anyone and not really sure it's in the same theme but.

Wouldn't it be easier to just build what we want underground on any small moon or planet?
Teraforming The underground in small steps.

So many plusses to building underground on Mars, Titan the Moon etc etc.
No giant Technical leaps for that either.

When you think about it, that is pretty much what we do here on Earth for the most part anyway.

We don't spend that much time on the surface here, more inside boxes we have built or underground or in transport getting to them.

Spatula · 2007-05-25 10:44:46

I think there's a lot that could be gained from that.

noosfractal · 2007-05-25 22:50:04

Wouldn't it be easier to just build what we want underground on any small moon or planet?

I think "thick-shell" habitats have the same problems in the long term - the costs of constantly guarding against vacuum - but they definitely have inherent safety advantages over thin-shells, and I admit they may be the most economical solution for a long time (hundreds of years).

It's also an open question as to whether we can adapt to microgravity. I personally imagine that it can only be health positive, but it could be that some essential aspect of our biology requires gravity at a certain level. If that's the case, then the role of aeroliths is probably limited to holiday resorts.

nickname · 2007-05-26 05:05:21

noosfractal,

A similar feeling i have about micro gravity.

I have a feeling on anywhere other than Earth we are going to be spending our sleeping hours in a large centrifuge at 1 g if we expect to stay somewhere for long periods of time.
A real unknown though for sure.

The biggest plus i see to thick shell is you can start small expand as needed and use pretty simple technology we probably have now.

Although the idea of a world we can walk on the surface and breath normally is very appealing.
Then we could probably pave it and drive to our concrete boxes in climate controlled transport LOL

karov · 2007-05-28 12:49:58

Firstly, if we are talking about heating an icy world to earth surface temperatures and melting it into a global ocean, where will the inhabitants get their mineral resources from? It would appear that they would sink to the bottom of a global ocean 100's of KM deep in mnay cases

1500km diameter, average density about 2 kg/L, surface gravity ~3% gee... normal distribution of 50% "ices" and 50% "rocks" ... typical icy mini-world... The solid core would be or would form at roughly the half of the depth... 3% of 350 km are equal presure-wise as about 10km ocean depth on earth.

Also the heat migration in the depths would not be easy. polar summer time permafrost.

Also, whatabout soil for growing crops?

The same source as usual, whatever that means... Importing "soily" chinks from outside is always usefull , deceleate them via space elevator and you got energy as profit.

The only other alternative would be to cover the icy surfcae in an artificial (metal?) crust, before heating takes place

pfu. aerogel layer. ( but not so necessary - covenction although slower but rather massive one due to the low gravity would track away the heat upwards). Also earthlike temperatures is quite conditional term - Iceland.

But then you run into the problem of what happens if the crust is pierced by a meteorite.

?????????

Antius · 2007-05-29 02:06:40

Sounds good. There appear to be no fundamental barriers against the terraforming of smaller worlds.

Ceres would appear to be the most promising initial candidate. It is close enough to the sun to provide acceptable levels of sunlight for plant growth and massive enough to allow the accumulation of an atmosphere with acceptable surface pressure without the requirement for ridiculous quantities of gas. To provide a 1 bar pressure at the surface of Ceres, a mass of gas equivalent to 1% of the mass of the Ceres would be required. For smaller worlds, the amount of gas needed becomes excessive for the amount of surface area gained and you end up building a small gas planet.

Ceres could be terraformed relatively easily given the relatively abundant sunlight at its orbit. If a large comet were trapped in orbit around Ceres, the sun would gradually vaporise it into ammonia, water vapour and various other minor gases. The UV and solar wind particles would ionise the gases. If a superconducting ring were placed around the equator of Ceres, the ions would tumble along the field lines, entering the atmosphere at the poles.

By this means, Ceres could be provided with a breathable oxygen/nitrogen/water vapour atmosphere in a relatively short timeframe (~decades), due to the potentially enormous catchment area of the magnetic field. The sun does all of the hard work breaking down the water and ammonia into oxygen and nitrogen.

With a diameter of 950km, the surface area of Ceres is almost 3million square kilometres. At typical European/Japanese population densities, this would provide living space for perhaps 1 billion people.

noosfractal · 2007-05-29 03:17:21

And it's located right in the middle of the asteroid belt.

It's low gravity and rotation period mean that geostationary orbit is at ~250km above the surface. That in turn means a no-taper space elevator would only need a material with a tensile strength/density ratio of 4000 Pa m^3 kg-1. Which is practically anything. Almost any metal could be used with a safety factor of 10 (i.e., 1000% over critical).

Antius · 2007-05-29 05:25:28

~250km may be within the Ceres atmosphere. The column density of the atmosphere would need to be 40 times that of the Earth in order to provide similar surface pressure. Given that the Earths stratosphere extends to 50km above the surface, we can expect the Ceres atmosphere to be at least 200km deep. The ionosphere and exosphere will extend even further.

It would be interesting to know how this would effect atmospheric dynamics. Would we get super-high winds in the atmosphere? How much dust and suspended water would the atmosphere hold and how would that effect transparency?

Given that a superconducting magnetic field will prevent the atmosphere from leaking into space even on relatively small bodies, the ultimate descision over whether or not to terraform a body, would come down to whether the value of each square mile of land, is worth the cost of providing a breathable atmosphere over the land. As the candidate body's get smaller, surface gravity goes down and the required column density of gas increases progressively. This in turn, will increase the cost per unit area. Eventually, the mass of the atmosphere is a sizable proportion of the mass of the entire body. As gravity decreases, it is also arguable that the desirability of the land goes down.

As i said before, the question will come down to economics, as do all things in life. For bodies like Ceres, Vesta, Juno, Pallas, etc, my guess is that it will be much cheaper just to dome areas off with plastic enclosures. Even for Mars, there is a strong case for paraterraforming over planetary terraforming. the obvious advantage is is that you do the job in an incremental manor, with a relatively small budget to begin with.

karov · 2007-06-07 06:02:21

http://www.spacedaily.com/reports/The_M … n_999.html

just an example about the wide spectrum of possible means to design artificial magnetospheres.

From the other hand WE HAVE coordinate center to estimate how magntically could be held atmosphere around small body:

M2P2 = http://en.wikipedia.org/wiki/M2P2

The critrion for stimatioj is comparativelly simple. Say, 1 Ceres = an atmosphere 1 Bar at surface will follow ~30 times less steep curve for thinning: i.e. it would be as thin as the Earths atmosphere at 1000 km hight -- about 30 000 km from the surface ot Ceres.

approx. as thick as the M2P2 bubble plasma. Power-sourcee the sun EM and particle radiation, source for replenishing the plasma bubble -- the very solar wind hydrogen and helium... etc. Designed well the 1 Ceres 60 to 100 thousand km wide artificial ionosphere ( which also genates the mag-sphere - NOT the core !) will serve also as pretty efficient power-generator for the colony, catching / sweeping the solar wind from many times wider crossseection, although thee rarifying of the wind at such bigger distance.

The artificial ionosphere / homeostatic upon the external source of energy / also could serve , specially regarding the 0.03 gees and counting down of gravity as stator / or fundament for lots and lots of SUSPENDED applications -- buterfly-wings-thin adjustable flaks / wisps serving as solar refractor / reflector orr both, plasma and aircon devices... refrigrator systems hanging in air on ~1000-2000 km hight to provide superdeep water / "strato"spheric cold-trap, etc. etc.

With mega-mega M2P2-type bubble I`ll try to figure out what and how much of air it could hold WITHOUT any central body... mini-gas"giant" of no-core , roof-less air-pocket oasis, self-sustaining powerwise, utilizing for shape-maintenance the very forces which otherwise just erode much solider and bigger objects` atmospheres.

If this is an invntion in habitat designing, please commenting it in other forums call it KAROV HABITAT ;-)
eveyone deserves his 3 min. of glory.

I`ll develop it in separate theme here in about a month term. I promisse.

Terraformer · 2012-08-25 13:54:01

As an alternative to magnetic field retention, how about relying on the old method of enveloping the body? No reason why there has to be only one layer - a couple of dozen layers would allow for a small pressure difference between the layers, and so the final differential might only be a few millibars, which will avert certain catastrophic failure modes.

However... given that water is paramagnetic, perhaps it would be possible to have an outer atmosphere composed of water vapour, retained by a magnetic field, for burning up small meteroids that would otherwise damage the worldhouse roof? Any other gas which responds well to magnetic fields would do, of course. If Argon is available, we could simply use that and ensure that nearly all of it is ionised; since it would be a monoelemental atmsophere, we wouldn't have to worry about other compounds forming. Thinking of which, Oxygen is also paramagnetic... but I'd be concerned with it's oxidising effect on the worldhouse. Still, if we're far out enough that the atmosphere doesn't get ionised much, perhaps it's one of the best options.

Another possibility for dealing with meteoroids is some sort of gel at the top of the worldhouse which would absorb the shock of the impact, distributing it around the entire body, whilest flowing to ensure a flawless surface afterwards.

If we can "terraform" bodies as small as 10km across, think of the worldbuilding applications. Hundreds, thousands of inhabited systems seperated by perhaps less than a million kilometers. Now that's a decent Hard SF setting. The worlds might only be vanity projects, but they should do quite well for weekend homes for those who spend their weeks in orbit around them. Perhaps, that close, people might choose to live there and commute to work each day in orbit, where they'll get their required excercise amounts in gravity.

Obviously, the environment on such a world would be rather odd - there could be no large open bodies of water due to the microgravity, although smaller ponds might be possible by using magnetic fields to hold the water in. I don't think it would be possible to make it rain, so it might end up a rather misty, humid place. Perhaps dehumidifiers would maintain the environment as desired by the terraformers. In the microgravity, flight would not just be easy but necessary, as well as claws to hold the animal to the ground or tree. Hooves are definately out. We'd have to breed and engineer many new species for these places. The trees would be able to get quite tall, and some cultures might choose to make them the base of the food chain.

Spaniard · 2012-08-29 08:27:24

I think that if the body is so small that any open terraformation is impractical, then underground colonies could be a better alternative.
With time, the underground colonies could be so big and cover so much surface than it could be considered paraterraforming with opaque roof.

If caves was big enough and well connected, even a common biosphere is possible.

Gigant stable caves are possible when gravity is so small.

karov · 2012-08-29 09:15:30

Spaniard,

So, what's the difference between digging in and covering/building over/around? If it is inflatable and fillable with , say, water or other balast dome-type of structure, it I believe, would be hundreds of times cheaper to erect, than to dig out the corresponding to the volume mass of rock/dirt...

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