New Mars Forums

Small bodies can hold on to atmospheres for geological timescales if protected by an artificial magnetosphere, see:
http://newmars.com/forums/viewtopic.php?t=5339

Even on a very small body, the entire atmosphere will not flash into space immiediately, but will slowly 'evapourate' from the top down.  Only molecules able to achieve a free path, will be able to succesfully escape.  This condition only applies to ions at the top of the ionosphere (exosphere).  If the world is supplied with a powerful artificial magnetic field, the atmospheric ions would be recycled continuously, spirally down the field lines until they re-enter the atmosphere at the poles.  This way, even relatively small bodies can retain synthetic atmospheres for geological timescales, although for bodies with surface gravity of less ~1% Earth, the amount of gas needed to produce an acceptable surface pressure becomes excessive.

I like the idea of using a strong greenhouse gas as a major atmospheric constituent.  But what would be the effect of solar UV on SF6?  Would we find ourselves with an atmosphere of SO2 and hydrogen flouride after just a few centuries?

As regards the use of mirrors, there is presumably a point, as one moves to bodies further from the sun, where it becomes more economic to artificially illuminate using a thermonuclear power source, rather than attempt to reflect the light of the sun.

I would also raise questions as to just how much rock is present on the surfcaces of Ganymede and Callisto.  Is there actually enough material there to form a significant crust?  I was under the impression that the surfcae of both worlds was icy, with small amounts of rock and dust present from meteorite fragments.

The gulf of intelligence is likely to be the other way around.  The more we learn about the Earth, the more we learn just how special it is and how small variations in certain attributes would render it unsuitable for complex, intelligent life.

Consider the following: For 90% of the Earth's existence it has held life, but for the first 4billion years, that life was single cellular and primitive.  Multicellular life did not evolve until about 500 million years ago and the first land plants apperaed a few hundred million years ago.  No-one knwos why, but it is suspected that a high concentration of oxygen in the atmosphere and low concentration of CO2, was a prerequisite for allowing multicellular metabolism.

Condition 1: Precise atmospheric composition.

Second, the Earth had to be large enough to hold a strong magnetic field and active geology for billions of years, yet small enough and outside of the star's hot zone to avoid accumulating a hot, dry, dense atmosphere like Venus, or excessive volcanism that would plague a larger than earth terrestial planet.

Condition 2: precise size and distance from star.

Condition 3: Jupiter.  Without a massive planet at about the right distance from the sun, the Earth would be slammed by comets on a regular basis.

Condition 4: A large moon.  Our moon is very large, compared to its planetary companion.  Lunar is as large as the moons of jupiter, a planet 300 times as heavy, and it formed under very unique conditions.  Without it, the Earth's axial tilt would be unstable and it would be subject to frequent and very intense climatic swings.

Condition 5: A stable star.  Only 15% of stars are as stable as our sun, most exhibit much more intense and frequent flaring activity, that would lead to climatic swings and would compress most planetary magnetic fields, leading to steady errosion of planetary atmospheres.

There are probably even more conditions that make the earth special, without which intelligent, complex life and a civilisation could not have evolved.

The impression that these facts tend to create is that primitive life is probably everywhere, advanced life is probably very rare.  There may be an intelligent civilisation with 100 light-years of earth.  I may win the lottery next week!

One obvious point occures to me, if a civilisation had evolved elsewhere in our galaxy in the past, then given the age of the universe, wouldn't they have litterally conquered the galaxy by now?  How come they havn't colonised our solar system long ago and how come the galaxy isn't awash with interstellar communication?  If even one advanced civilisation had evolved and become space faring as little as 1 million years ago, we would expect them to be everywhere by now.  This suggests that we are the first spacefaring civilisation to have evolved in this galaxy.

Sure, we could discuss terraforming from the point of view of having infinite money, resources, technologies unbounded by the laws of physics, etc.  Then we would be gods, by any measure.

In the real world, whether it be the world of today or the solar system 5000 years hence, cost (in terms of required resources) and investmnet timeframe, are always going to be important.  These hark back to basic laws of nature, they are not simply constructs of short-sighted capitalism.

We need to have some measure of reality in these discussions, for there to be any point having them at all.

In all terraforming scenarios the viability of a project = f(value of terraformed land/cost x return timeframe).

At some point it becomes easier simply to build your own world and craft it as you please.

Maybe a 1 bar atmosphere won't be neccesary for Mars.  On skylab, the crew survived perfectly well in a 1/3rd bar atmosphere, two-thirds oxygen, one third nitrogen.

The idea of decaying cometary objects in orbit is much better than slamming them into the surface.  If Mars can be given a significant magnetic field, then the sun can do the hard work of breaking down the ammonia and water into breathable oxygen/nitrogen.

The most important hurdle in terraforming Mars is getting it to the point where it can support advanced plant life in open air.  Once that is achieved, we can grow crops outside of domes, which massively improves the economics of habitation.

True.  You would probably end up displacing entire cities, maybe even entire new nations!

Some form of terraforming would appear desirable at an early stage on Mars.  The present atmosphere is too thin to provide any plausible shielding against cosmic rays or solar flares and may even aggrevate the situation by breaking down into secondary particles.

Also, thickening the atmosphere could be accomplished relatively easily, with half a dozen CFC producing nuclear-powered factories on the surface.  As soon as major flourine/chlorine salt mineral beds are identified, the factories could be shipped up from earth at an acceptable cost and landed enpiece at the location of the mineral bed.  The atmosphere could be substantially thickened within a few decades, at an affordable price.

Again, there are strong economic imperitives, for the simple reason that the value of the land increases dramatically if radiation levels go down and especially if hardy food crops can be grown outside of man-made structures.  The cost is affordable and the results are near-term enough for the project to be taken seriously.

Shifting large asteroids and producing a breathable atmosphere are longer term options that are probably unrealistic as conscious projects by any government.  They are also unneccesary, given that humans can create a comfortable environment relatively cheaply and incrementally using plastic domes.

Mars will be paraterraformed long before any serious planetary terraforming is attempted.

This makes sense.  I know that many would argue that an icy terraformed world has long-term security advantages over a thin-shelled habitat, but in the short to medium term, an O'Neill type habitat is overwhelmingly attractive, in terms of initial cost and living conditions.  It would appear to offer far more in terms of value for money.  They are also incremental - you can buildf them one at a time, eventually building up a massive amount of land.  Contrast this to any terraformed world, whose land will not be available for habitation until the enormous task of terraforming is completed, probably centuries in the future.

It is rather hard for me to imagine, what sort of society would go to so much cost and expense creating what is sure to be a cold and miserable little planet.  It is easier to imagine an incremental terraforming approach on Mars, where the atmosphere would be initially thickened to provide cosmic ray shielding and could be accomplished relatively easily, simply by pumping CFCs into the existing atmosphere.  But most other worlds (the jovians, satellites of saturn, uranus, neptune, pluto and the TNOs) will always be cold, miserable and rather unproductive even after full terraforming is complete.  Mars isn't the only candidate, but it appears to be the only one that offers value for money.

It sounds ridiculous, but it would appear no less possible than terraforming Jupiter's other large moons.  Amalthea has the dimensions 250x146x148km and its surfcae gravity is 0.02m/s2.  This is 1/500th of Earth's gravity.  The column density of the atmosphere would therefore need to be 5000tonnes/m2 for a 1bar average surface pressure.  the total mass of the atmosphere would 5x10(17)kg - fully a quarter the mass of the satellite!  The escape velocity of Amalthea is just 50m/s, so the atmosphere would escape very rapidly without a magnetic field holding it in place.

The views of Jupiter would be stunning!

As a target for human colonisation, Europa strinkes me as the least promissing of all of the Jovians.  It is relatively small, has a young and therfore mineral depleted icy crust and is right in the middle of Jupiter's radiation belts.  Callisto is probably the most appealing target, Ganymede a distant second.

The Sea Dragon Big Dumb Booster idea may very well be the way to go.  Large, but simple pressure-fed engines, with ablative liners, may end up being cheaper per unit of payload lifted than much smaller, high performance engines, which are really only suitable for ballistic missiles.

I have often wondered why NASA has not given more attention to the Big Dumb Booster concept.  The shuttle has demonstrated that the technological requiremnets of a reusable vehicle almost automatically make it an expensive vehicle.

Instead, we want rockets rather like coke-cans, which we can use once and then throw away.  This sort of design philosophy does not lend itself to complex, turbo-pump rockets made from ultra-expensive alloys.  Ultimately I think, even a very large rocket could be extremely simple in design, with only a handful of moving parts (valves on the propellant lines, tank pressurisation equipment and a valve within the engine).  Once the design is finalised, the whole thing could be constructyed in a ship yard from carbon steels or aluminium, very cheaply.

~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.

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.

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.