Terraforming Jupiter's Moons

Antius · 2007-05-31 10:07:10

Given Venus's hostile environment, relatively deep gravity well and general lack of anything exceptional that it might export, I would anticipate that this will probably be a deadzone for future human colonization.
We have an entire other thread for this. Feel free to bring this up there, since you haven't yet. I've already spent a lot of time developing my case for Venus, and there's plenty more I haven't discussed yet.
Although if you want to talk about 'costing too much', you're on the wrong forum. Terraforming any planet is going to be incredibly expensive. We can't even imagine the costs properly. Every planet is a gravity well. Terraforming Mars at all would seem completely without economic merit, compared to mining all the low-gravity bodies, ignoring the neighboring planets, and calling it a day.

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.

Spatula · 2007-05-31 12:55:43

You're forgetting time. Investments that take thousands of years to pay off, but keep paying for billions of years are very worthwhile. What we're talking about is expensive, but there is no scarcity of resources to hinder it. Everything we need is right here in the solar system in abundance, and can be collected without straining our resources. Instead it becomes a function of the amount of time paying resources in, and the amount of time profiting from them.

When we talk about terraforming, we should be talking in terms of results, because the quality of those results reflects the cost a lot more heavily than the short term costs in getting them.

Venus and Mars can both be terraformed, no question of if. One of them will have enough gravity to walk normally on, enough to reproduce without possibly bad side effects, and enough geological activity to keep the surface rich in important minerals. One will be a lot more comfortable, but that doesn't rule the other one out. A lot of comfort can be lost before a planet becomes inhospitable. Neither would ever be as comfortable as Earth, certainly.

And neither will be terraformed in our lifetimes. It'll take probably thousands of years. It'll take hundreds of years just for us to get the economic strength to start. By the time we can even debate starting, we'll have a massive space economy, hundreds of times more capable of moving resources than our current one, automated, always advancing. At that point, terraforming simply becomes logical, as there's nothing else to do with the massive resources we can tap.

samy · 2007-05-31 18:25:25

Investments that take thousands of years to pay off, but keep paying for billions of years are very worthwhile.

What company or government do you expect to be around for those billions of years, so they could reap the rewards?

If reaping the rewards is going to take longer than you have, the amount of those rewards is irrelevant. A 120-year old guy isn't going to make a big investment that takes 100 years to pay off.

So rewards that pay off over a geological period of time are irrelevant economically to any entity engaging in them.

StarDreamer · 2007-05-31 19:34:30

Terraforming Venus would be a nightmare of a project. How exactly do we dispose of a carbon dioxide atmosphere with a column density of 1000tonnes per square metre?
To introduce sufficient water to Venus would require the equivelent of several large kuiper belt objects, all of which would presumably need to cross Earth's orbit to get there.
Even after terraforming, the planet would still be unbearably hot, with the surface temperature teetering around the boiling point of water in equatorial regions. Then you have to deal with the fact that Venuses day-length is roughly comparable to its year (~250days).
Given Venus's hostile environment, relatively deep gravity well and general lack of anything exceptional that it might export, I would anticipate that this will probably be a deadzone for future human colonization.

Antius -- you haven't been following the "thought history" on this one. We were debating in another thread whether it might be better to colonise Venus "as it is" and nevermind terraforming it. It goes like this: on Venus, Terran atmosphere is a "lifting gas". On Earth, only H2 and He give good lift. On Venus, the whole Terran air mixture of O2 and N2 will lift a bubble. Therefore, we can build floating habitats in the upper atmosphere of Venus, where the pressure is 1-3 bars, the temperature is about 50C, but the gravity is still +90% of Earth's. This is at 50km or higher. Within the bubbles, no pressure suits or breathing apparatus would be required. Bubble breaches would need speedy repair but yet would not be catastrophic failures. The colonies would be widely decentralised, rather than huddling everyone into a single point domed city. Some on here have spoken of Cloud City or Manhattans in the Sky, but I do not see anything so ambitious. What I see is a swarm of ovoid bubbles (eggs) with specialist purposes -- bubble farms, bubble trading posts, bubble carbon scrubbers, bubble factories, bubble spaceports, bubble laboratories, bubble fuel depots, ... mostly untethered and floating freely. There is greater security in numbers and in not concentrating resources.

Raw material resources and energy are nearly unlimited at Venus -- solar radiation, oxygen, carbon, nitrogen (3 bars worth). We never have to go down to the surface. Indeed -- there is no intention to do so. Venus has in abundance what we need as a species to terraform Mars and Ceres and beyond. It may happen that Venus gets terraformed eventually, over time and perhaps as a byproduct of human industrial activity. (Indeed, some may argue that we are veneraforming Earth via global warming!) But that will not be the purpose of going there. That will come about on initiative of the colonists themselves many centuries from now, once they feel they "own" Venus and want to improve it.

The gravity well may be deeper at Venus, but it is not so bad at 50km up and the depth of the well is inconsequential if the resources for overcoming it are in cheap abundance and close to hand. What is more important to consider is the "technology hill": what do we know we do not yet know but need to know in order to make it a go? What are the logistical barriers? And how much local "in situ" initiative, control, sustainable growth, self-sufficiency, industry can the colonists take upon themselves and how quickly? My suspicion is that a Mars colony has a century of dependency ahead of it in all things, including food, fuel, etc. If it costs billions to build one nuclear reactor on Earth, how shall we get 12 built on Mars? But Venus? Solar radiation and heat are cheap there. Self-sustainable food and energy can be achieved within a decade of arrival on Venus. Why? Because on Venus we can grow the infrastructure and the population base at the same rate. We can multiply bubbles a lot faster than caves or pits in rock.

The challenges to this scenario on Venus are the sulphur clouds in the upper atmosphere, the possibility of high wind shear and downdrafts, and the lack of water. Water can be extracted from the sulphuric acid clouds (H2SO4). Long-term effects of acid clouds on bubble materials and equipment are a serious concern -- what do we make these bubbles out of? Fullerene? And coping strategies for storm turbulence. But this is much less than what we face at Mars!

~~ Bryan

Spatula · 2007-06-01 00:15:06

Investments that take thousands of years to pay off, but keep paying for billions of years are very worthwhile.
What company or government do you expect to be around for those billions of years, so they could reap the rewards?
If reaping the rewards is going to take longer than you have, the amount of those rewards is irrelevant. A 120-year old guy isn't going to make a big investment that takes 100 years to pay off.
So rewards that pay off over a geological period of time are irrelevant economically to any entity engaging in them.

For the good of humanity then? For science? We're spending a significant amount of money researching fusion, and it's not going to pay off until late in our lifetimes, if at all. Much of this is a logical extension of the increasing scale that our economy operates on.

Of course human lifespans will increase too.

Really, your view of human reasoning is too narrow. We're completely capable of applying foresight beyond 100 years, and while there are short term reasons we could choose to not act on it, that would seem to defy our natural curiosity.

RobertDyck · 2007-06-04 15:18:07

You can terraform Ganymede and Callisto.

Since Jovian moons are in orbit around Jupiter, their mean distance from the sun is the same. That is 5.2028 times the Earth's distance. The inverse square rule means they receive 1/27.06912784 as much sunlight per unit area as Earth, twilight. That's damn little, but it can be augmented. A series of concentric ring in polar orbit, connected and providing mutual support, can form a parabolic mirror. The centre of the parabola will be shadowed by the moon so it would be cut out. The rest of the parabola would have more depth than the diameter of the moon. This prohibits satellites, but would dramatically increase light. With a parabola diameter 3 times the diameter of the moon, total light gathering area including the planet itself will be 9 times the surface area. This will increase solar energy to 9 times current. That would still be 1/3.00768 per unit area that of the Earth, but sufficient. The planet would be brighter than an office except for a brief night when passing through the circle that doesn't receive reflected light. It's a big engineering project, but possible.

Europa has a pure ice crust about 7km deep, possibly as deep as 10km in places, which if melted would form a moon-wide ocean. Ganymede and Callisto have dirty ice about 500km deep inferred by gravity and density, with a rocky surface. Surface conditions of those two moons could be controlled to provide temperate conditions. After all, the Earth is 12,750km in diameter with a crust 24km thick; beneath that is magma. If the Earth can have a cold surface with ice insulated by a few kilometres of rock, then Jovian moons could have a temperate surface with cold ice interior insulated by rock and dirt.

The greater problem is holding on to an atmosphere. Ganymede has a surface gravity 0.146 Gs, Callisto has 0.127 Gs, and Europa has 0.13 Gs. An atmosphere of xenon would stay put, the question is where to find enough of it. Sulphur hexafluoride (SF6) is an even heavier gas, Io has plenty of sulphur but I don't know the abundance of fluorine. Xenon density is 5.894 g/L, SF6 is 6.164 g/L, nitrogen is 1.251 g/L and oxygen is 1.429 g/L. SF6 is also the strongest greenhouse gas we know, is highly inert, quite safe. It sublimes at -63.9°C. Unlike many other sulphur compounds, it's colourless and odourless. Solubility in water is low, so it wouldn't dissolve in an ocean.

Spatula · 2007-06-04 23:00:24

I've never been very keen on 'giant mirrors and lenses' in space. Where would the metal come from? How would you keep them from collapsing under their gravity? How would you keep them tidally locked to the body you're terraforming?

Just for the heck of it, does Jupiter emit a significant amount of infrared, by any chance? It'd be interesting if such a planet could be used as a makeshift star.

Antius · 2007-06-05 01:13:04

You can terraform Ganymede and Callisto.
Since Jovian moons are in orbit around Jupiter, their mean distance from the sun is the same. That is 5.2028 times the Earth's distance. The inverse square rule means they receive 1/27.06912784 as much sunlight per unit area as Earth, twilight. That's damn little, but it can be augmented. A series of concentric ring in polar orbit, connected and providing mutual support, can form a parabolic mirror. The centre of the parabola will be shadowed by the moon so it would be cut out. The rest of the parabola would have more depth than the diameter of the moon. This prohibits satellites, but would dramatically increase light. With a parabola diameter 3 times the diameter of the moon, total light gathering area including the planet itself will be 9 times the surface area. This will increase solar energy to 9 times current. That would still be 1/3.00768 per unit area that of the Earth, but sufficient. The planet would be brighter than an office except for a brief night when passing through the circle that doesn't receive reflected light. It's a big engineering project, but possible.
Europa has a pure ice crust about 7km deep, possibly as deep as 10km in places, which if melted would form a moon-wide ocean. Ganymede and Callisto have dirty ice about 500km deep inferred by gravity and density, with a rocky surface. Surface conditions of those two moons could be controlled to provide temperate conditions. After all, the Earth is 12,750km in diameter with a crust 24km thick; beneath that is magma. If the Earth can have a cold surface with ice insulated by a few kilometres of rock, then Jovian moons could have a temperate surface with cold ice interior insulated by rock and dirt.
The greater problem is holding on to an atmosphere. Ganymede has a surface gravity 0.146 Gs, Callisto has 0.127 Gs, and Europa has 0.13 Gs. An atmosphere of xenon would stay put, the question is where to find enough of it. Sulphur hexafluoride (SF6) is an even heavier gas, Io has plenty of sulphur but I don't know the abundance of fluorine. Xenon density is 5.894 g/L, SF6 is 6.164 g/L, nitrogen is 1.251 g/L and oxygen is 1.429 g/L. SF6 is also the strongest greenhouse gas we know, is highly inert, quite safe. It sublimes at -63.9°C. Unlike many other sulphur compounds, it's colourless and odourless. Solubility in water is low, so it wouldn't dissolve in an ocean.

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.

Antius · 2007-06-05 03:14:45

You can terraform Ganymede and Callisto.
Europa has a pure ice crust about 7km deep, possibly as deep as 10km in places, which if melted would form a moon-wide ocean. Ganymede and Callisto have dirty ice about 500km deep inferred by gravity and density, with a rocky surface. Surface conditions of those two moons could be controlled to provide temperate conditions. After all, the Earth is 12,750km in diameter with a crust 24km thick; beneath that is magma. If the Earth can have a cold surface with ice insulated by a few kilometres of rock, then Jovian moons could have a temperate surface with cold ice interior insulated by rock and dirt.

Maybe one way around this problem would be to engineer a ‘sub-zero’ ecosystem. The idea being to genetically modify plants to incorporate ammonia or some other anti-freeze within their cells and sap. The ecosystem could then function at sub-zero temperatures, with plants surviving in icy soils.

The world would be artificially illuminated with ultraviolet light and the higher end of the visible spectrum, to deliver a maximum of photosynthetically available light, without raising the temperature of the world above freezing.

If this proves possible, it would allow even the iciest of moons and trans-Neptune worlds, to be terraformed without melting their surfaces into global oceans.

RobertDyck · 2007-06-05 04:57:11

Small bodies can hold on to atmospheres for geological timescales if protected by an artificial magnetosphere

I agree a magnetosphere is a good idea, in fact Jupiter has a lot of radiation so you also need the magnetosphere to protect against that. Jupiter's strong magnetosphere collects radiation belts, great to protect Jupiter but bad for anyone in Jupiter's orbit. But if you terraform a planet, you really need to plan for more than just a few thousand years. There are limited resources on a planet, expending them just to be released into space is irresponsible. Terraforming has to be for the long-term, lasting millions of years if not hundreds of millions.

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?

Good question. I checked, SF6 is inert toward oxygen, it takes a platinum catalyst to get them to react and a lot of energy. The abstract for this paper talks about electrical explosions of platinum, and temperatures above 5000°K.
http://stinet.dtic.mil/oai/oai?&verb=ge … =AD0680768

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 visible surface is entirely rock, the belief that there's ice present is based on density calculated from gravity. In fact they don't have any direct evidence of ice on Ganymede or Callisto.

I've never been very keen on 'giant mirrors and lenses' in space. Where would the metal come from?

Jupiter's small moons, which are basically captured asteroids.

Maybe one way around this problem would be to engineer a ‘sub-zero’ ecosystem. The idea being to genetically modify plants to incorporate ammonia or some other anti-freeze within their cells and sap. The ecosystem could then function at sub-zero temperatures, with plants surviving in icy soils.
...
If this proves possible, it would allow even the iciest of moons and trans-Neptune worlds, to be terraformed without melting their surfaces into global oceans.

That works with temperatures just a couple degrees below freezing, so the antifreeze keeps water liquid. Ganymede's temperature currently is between 90°K and 160°K, that's -183°C to -113°C.

Antius · 2007-06-05 06:30:01

Small bodies can hold on to atmospheres for geological timescales if protected by an artificial magnetosphere
I agree a magnetosphere is a good idea, in fact Jupiter has a lot of radiation so you also need the magnetosphere to protect against that. Jupiter's strong magnetosphere collects radiation belts, great to protect Jupiter but bad for anyone in Jupiter's orbit. But if you terraform a planet, you really need to plan for more than just a few thousand years. There are limited resources on a planet, expending them just to be released into space is irresponsible. Terraforming has to be for the long-term, lasting millions of years if not hundreds of millions.
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?
Good question. I checked, SF6 is inert toward oxygen, it takes a platinum catalyst to get them to react and a lot of energy. The abstract for this paper talks about electrical explosions of platinum, and temperatures above 5000°K.
http://stinet.dtic.mil/oai/oai?&verb=ge … =AD0680768
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 visible surface is entirely rock, the belief that there's ice present is based on density calculated from gravity. In fact they don't have any direct evidence of ice on Ganymede or Callisto.
I've never been very keen on 'giant mirrors and lenses' in space. Where would the metal come from?
Jupiter's small moons, which are basically captured asteroids.
Maybe one way around this problem would be to engineer a ‘sub-zero’ ecosystem. The idea being to genetically modify plants to incorporate ammonia or some other anti-freeze within their cells and sap. The ecosystem could then function at sub-zero temperatures, with plants surviving in icy soils.
...
If this proves possible, it would allow even the iciest of moons and trans-Neptune worlds, to be terraformed without melting their surfaces into global oceans.
That works with temperatures just a couple degrees below freezing, so the antifreeze keeps water liquid. Ganymede's temperature currently is between 90°K and 160°K, that's -183°C to -113°C.

An interesting abstract on Callisto. The surfcae appears to be completely covered with rock and dust, with significant carbonaceous material also present.

http://www.lpi.usra.edu/meetings/LPSC98/pdf/1866.pdf

StarDreamer · 2007-06-05 09:22:38

Europa has a pure ice crust about 7km deep, possibly as deep as 10km in places, which if melted would form a moon-wide ocean. Ganymede and Callisto have dirty ice about 500km deep inferred by gravity and density, with a rocky surface. Surface conditions of those two moons could be controlled to provide temperate conditions. After all, the Earth is 12,750km in diameter with a crust 24km thick; beneath that is magma. If the Earth can have a cold surface with ice insulated by a few kilometres of rock, then Jovian moons could have a temperate surface with cold ice interior insulated by rock and dirt.

Is this a typo -- "500km"? They are each larger than Europa and Europa's ocean is already impressively deep.

~~ Bryan

RobertDyck · 2007-06-05 09:54:37

Is this a typo -- "500km"? They are each larger than Europa and Europa's ocean is already impressively deep.
~~ Bryan

Not a typo. They're always discovering more, but after the Galileo flyby they measured gravity in detail and attempted to extrapolate the interior. I remember reading they said the mantle was a mixture of ice and silicates about 500km deep. When I look now it says:

http://www2.jpl.nasa.gov/galileo/ganymede/fact.html

Ganymede is the largest satellite in the solar system with a diameter of 5,268 km (3270 miles). It is larger than Mercury and Pluto, and three-quarters the size of Mars. If Ganymede orbited the Sun instead of orbiting Jupiter, it would easily be classified as a planet.

Since Ganymede has a low density of 1.94 grams/cubic centimeter (water's density = 1.00), it was originally estimated that the satellite is half water ice with a rocky core extending to half of the satellite's radius. However, the first two flybys by Galileo had detected a magnetic field around Ganymede, which strongly indicates that the satellite has metallic core about 250 to 800 miles in. The mantle is composed of ice and silicates and a crust which is probably a thick layer of water ice.

250 to 800 miles is 402km to 1287km. The question is whether there's a layered mantle, is it rocky silicates close to the metalic core with ice and silicates closer to the surface, or is it more evenly mixed? The picture depicts a brown rocky inner mantle, blue icy outer mantle, and white ice crust covered in a layer of dust. That's still a guess based on density and magnetic field, what they see on the surface is regolith.

Spatula · 2007-06-05 12:11:21

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.

If heated to Earth temperatures and pressures, they would have deep oceans covering the entire surface.

The visible surface is entirely rock, the belief that there's ice present is based on density calculated from gravity. In fact they don't have any direct evidence of ice on Ganymede or Callisto.

They have lots of evidence for large amounts of water on the moons: induced magnetic fields caused by deep oceans just under the crust, reacting with Jupiter's magnetic influence. These oceans would only be sustainable with pressure from massive icy crusts.

Much as you might protest, the gravity measurements really make it look like they're full of water. Other explanations for their lack of density are less likely. The decreasing density of the moons as you move further from Jupiter fits a pattern of Jupiter's early heat clearing volatiles from the interior of the system. The pattern of gravity from the moons indicates the separation of layers in their interiors by density, caused by Jupiter's tidal stresses. Callisto obviously is less differentiated due to its distance from the planet and other moons.

There could be something else causing this, but it's unlikely. The crusts are made of a combination of types of ice that form at low temperatures and pressures. Pressure beneath the crusts causes ice to form oceans. Pretty straightforward, and generally accepted as the scientific consensus.

RobertDyck · 2007-06-05 23:00:24

Actually I said it is most likely that there is ice and silicate mixture for about 500km from one report, 402km to 1287km from another report. Despite which report you want to believe, it's still hundreds of kilometres. Stop thinking of melting everything, temperature will never be even throughout. As I pointed out, the Earth is 12,750km in diameter at the equator but only the top 24km is crust. The mantle is ridiculously hot; I don't know if it's all magma but it is the source of volcanoes. Despite this fact the surface is temperate and winter is freezing cold. Reverse that with Ganymede and Callisto, I expect they are frozen right through now and you aren't going to heat anything as big as a small planet within the life span of our species. However, you can melt the surface. Here in Canada the ground freezes about 3 feet deep in winter, even on the coldest nights of the coldest years when we get temperatures down to -40°C. Actually we had temperatures of -40.4°, -40.6°, and -41.0°C respectively for three successive nights at the end of January 2005. The ground is just black top soil for a few inches, then gumbo (black clay) all the way down to bedrock. That's enough to keep the deep soil warm, and the deeper it gets the warmer it gets. So control conditions to keep the deep ground of Ganymede frozen solid while the surface is temperate. Will that require deliberately causing a winter cycle to release heat? Just keep a fixed depth frozen solid so it doesn't melt into an ocean hundreds of km deep. During winter cycles, the deep crust will absorb heat as well as releasing heat from the surface. The mantle is one hell of a heat sink; I don't think you'll melt it any time soon. Let's see, 1287km depth of ice and rock mixture starting between -183°C and -113°C; how long do you think it'll remain below 0°C with clay, dust and rock insulating it from a warm surface, especially with periodic winter temperatures to release surface soil heat to space?

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