Which planet in this solar system would be most appropriate to terraform?

Gliese123

I've been reading about terraforming and really stuck with it. Which planet /moon has the most convenient conditions, such as mass, magnetic field, gravity, intensity of sunlight for possible terraform. Venus, Moon or Mars or some else? Which one do you think? And would it be possible?

Basic gravity conditions (which decides the ability to remain a atmosphere also all bodies are without considerable magnetic field):
Venus: 8.87 m/s²
Moon: 1.622 m/s²
Mars: 3.711 m/s²

qraal

They were arguing this in General Engineering, but from an astronomical point of view I would claim that Venus was easier. But it depends on which bit of a planet is the most important. Venus has the most similar gravity to Earth and more than enough air. It does lack water, but that might not be such a big impediment, if some water can be supplied - a desert planet is more stable against runaway greenhouse at high insolation levels than a wet one. The chief problem is what one does with all the excess atmosphere. In theory the atmosphere should undergo collapse if the insolation reaching the surface can be reduced. If the upper atmosphere can either absorb the light that gets through to the ground at present or reflect it, then gradual atmospheric collapse should occur. But gradual. It'll probably take centuries for it cool and react with the soil, eventually forming carbonates, which is what the current atmosphere is believed to have been decomposed from millions of years ago.

Both Mars and the Moon need too much air to be added, and Mars needs more energy input, to really be front-runners. I know that's not what's generally assumed, but the logistics of supplying extra volatiles to either, and energy to Mars, is quite extraordinary.

So that's my opinion, astronomically/planetologically speaking.

meWyatt

I would think that Earth would be the place to start. If we cannot maintain its stability as a place congenial to human and most other existing life, then why would we allow such experimentation elsewhere? On the other hand, we've already done one significant experiment. Given enough gasoline and people driving cars, coal burning, mining and cow farts, we know we can bootstrap a process of warming on Mars. Can we survive on Earth long enough to reap the benefits? Probably not if at the same time we we are building that highway to Mars.

PSLock

Yes Venus would be the best bet in the inner solar system although I'm not sure how to speed up its rotational speed as would be needed to hopefully create an electromagnetic field as well as protect it from atmospheric collapse.
In the outer solar system Titan around Saturn is by far the best bet chemically as it is almost identical to earth 4.5 billion years ago. But if you were able to construct some type of barrier around IO to collect the charged particles stripped off of it by Jupiter to hopefully lower the ambient radiation levels around Jupiter system and to generate energy, Europe or Ganymede, or even possible Callisto could make great locations. At least that's my 2 cents. hope you like.

Gliese123

Titan is a really cool moon. It would probably be a candidate for such terraform. Still, it has no magnetic field and barely massive enough to hold an atmosphere for to long. I've read somewhere that it loses big amounts of its atmosphere every day. Why is it so? Does Jupiter tear it apart? Sadly, the moons in this solar system has to little mass I assume. Venus for sure. It would probably be mainly a desert planet then, right?

Gliese123

I guess- lack of mass and magnetic field= hard to do something.

Gliese123

Highway to Mars wouldn't be so bad? :D You're right, Earth need to be taken care of. And as soon as there are so much people living on this poor planet. I guess countries has to stop compete about the planet's resources and start to cooperate. But it's to much conflicts for that bright thought to come true I suppose....

Gliese123

Also, thank you for your informative facts :)

2milehi

Titan orbits Saturn

qraal

Titan's gravity is pretty low and the top of the atmosphere needs to stay cool or else it will escape. Some hydrogen does escape even now, but heavier gases should be retained if the upper levels can stay cool. As for magnetic fields, the solar wind is 100 times weaker than at Earth's orbit, so there's no erosion issues.

eachus

There are low-lying areas on Mars which could be cheaply terraformed, for example the Hellas Basin is about 10 miles lower than the surrounding highlands. Rather than trying to contain the atmosphere, you could create "blankets" filled with hydrogen and made of thin polymer, that were say a square kilometer each. Some hydrogen would escape, but much less than without the covers. Make them reflective only at night, and you would soon have termperatures above freezing in the valley.

Repeat for other large valleys and eventually you have more habitable land than on Earth.

On Venus, there is another choice. Build large enclosed structures containing an atmosphere like that of Earth. It will have significant positive lift at altitudes which are at Earth normal pressure and temperature. The problem is the super-rotation of the atmosphere. It rotates around the planet in less than a week, while a day is close to or identical to a local year. This means your areostat is going to need to be big, and sturdy, and fabricated somewhere other than on Venus.

But if you want to think big, what you do is this. Go to Saturn, throw large lumps of ice from the rings at Venus. Aiming carefully, you can get the planet's rotation up to a day or so. While you are at it, do the polymer blanket trick, but black at night, reflective by day. Eventually you get a big rain, with sulfurous and carbonic acids filling the lowlands and making them seas. How do you get rid of all that acid? Some will react with the rocks, forming water, but you need to get rid of quite a bit more than that. There is enough nitrogen already for an atmosphere, but you need to use sunlight to split some of the acids into H2O (water) sulfur, carbon and oxygen. You could combine the sulfur and carbon to form CS2 which is nasty stuff, but better would be to make big piles of sulfur and carbon (coal).

You could also form caverns inside Earth's moon, and that will probably be done at some point. But living at less than about Mars gravity will result in adverse health effects, so Mars or Venus is better for long time habitation.

Oh, and don't forget about Mercury. There are areas near the poles that should be habitable (for humans).

qraal

Nice. A Hellas dome/cover would be quite an amazing piece of architecture.

Aerostat colonies are a precondition of any Terraforming effort I would think, else one has to wait a long time for real estate.

Not physically feasible I'm afraid. The energy required would need very large masses of ice striking the planet, which I doubt would impress the people in the aerostats.

The amount of H2SO4 isn't very high, a few centimeters at most. And "carbonic acid" - carbon dioxide dissolved in water - needs a lot of water. Depending on the porosity of the regolith, most of the condensed water/carbon dioxide could end up soaked into the ground, rapidly combining with the salts there to make carbonate.

But condensing the atmosphere seems a good start to changing Venus. Importing water, though, might be unnecessary if we can import hydrogen instead and react it with the CO2 via the Bosch reaction. However the amount of carbon generated might have issues. If we could convert carbon dioxide directly into amorphous carbonia, then the job might be easier. I am unsure if the stuff is metastable enough at low pressures to be interesting, though if it could be confined inside buckyballs and nanotubes, then we're talking. The pressures inside such molecular cages can be thousands of bars, enough perhaps for stable carbonia at STP. Making buckyballs and nanotubes from carbon dioxide, of course, leaves free oxygen.

Any clever physical chemists on this board?

Sort of. The ground is cool, but the Sun is still hot. And making Mercury retain an atmosphere so close to the Sun would be quite a trick. MESSENGER should hopefully tell us more about the volatiles available near the Hermean poles.

eachus

I was trying to describe a solution that doesn't require a one-piece dome. You make "blankets" of thin polymer with pockets full of hydrogen. If you use electrolysis to make oxygen, you release both H2 and O2. The blankets float on the H2/O2 interface in the atmosphere, and both reduce the mixing (which is a good thing ;-) and allows the hydrogen to escape. Technically some will escape completely from the atmosphere, but most will end up over some other part of Mars, and reacting with the CO2 or the iron oxide on the ground, eventually ending up as water in the (Martian) atmosphere. Recycle as above.

At some point you do have a complete dome over Hellas, with several thicknesses of blankets, but no significant pressure difference. Since Hellas is plenty deep, the pressure at ground level could reach Earth levels. Of course, the first goal would be around 6 pounds of pressure with 50% O2. From that point on you want to add mostly nitrogen or inert gasses.
Glad I had finished drinking my tea when I read this--I would have needed to clean my keyboard. ;-)

Obviously the two approaches are mutually exclusive or need to be correctly coordinated. Who knows, maybe you could sell living space in the areostats with bonus fireworks displays daily and special effects. ;-)

The use of tethers reduces the required energy input at the Saturn end. The ice will melt in transit, and if you first wrap the ice in plastic, the energy will be dissipated high in the atmosphere. Of course, the coupling between the atmosphere and the planet doesn't seem to be all that great today. So maybe you want to use sunshades or wrappers reflective on the sunward side to get supercooled ice bombs.

The necessary angular momentum is not an issue--assuming you can do the rest of it. If you are going to move 3% of the mass of Venus from Saturn's rings the rest is detail. (And probably tree-hugger lawsuits to prevent "destruction" of the rings.)
Actually latest reports show more SO2 than H2SO4. A detail unless the reaction with rocks sops up all that precious oxygen you are making. As for the excess carbon from using CO2 as an oxygen source--both for free oxygen and water--make it into diamonds or diamonoid for construction materials. Waste not, want not. ;-)
I'm assuming a (partially) reflective dome. You want to let through about the same amount of sunlight as at the Earth's surface. If you want more than say, one hundred square kilometers for growing things, try some other planet, or the moon.

Note that once we build a space elevator at Earth, projects on this scale seem a lot more feasible. Any day now some company is going to start selling a (single multi-walled) cheese slicer.* Then building a space elevator will just be engineering.

* Of course, in today's litigious society, the cheese slicer may never make it to the stores. Yes, it will be much less dangerous than the kitchen knives on the next shelf,... Eventually you will need a weapons permit for those knives, and the cheese slicer too. That's why it is time to leave Earth.

Chronos

Introducing an atmosphere would be a huge engineering [and energy intensive] challenge. Venting some of the atmosphere from venus seems much more practical - and offers a potentially useful energy source for other teraforming activities.

qraal

We're on a physics board and you're making that claim? It's the silliest truism that has floated around discussions like this for years. Quantify it and see if it is true. Escape energy from Venus is 54 MJ/kg. Adding enough hydrogen to convert the carbon dioxide into water and carbon needs four hydrogen atoms for every pair of oxygens in the CO2. Thus 1/11 the mass of CO2 in hydrogen needs to be imported from a gas giant. Uranus has the lowest escape energy per unit mass which, after correcting for its rotation, is 173 MJ/kg and not much extra for a minimum energy transfer to Venus. About 200 MJ/kg - but remember we only need 1/11 the mass of carbon dioxide in hydrogen - thus just 22 MJ/kg for sufficient hydrogen delivery to Venus to convert its atmosphere.

Thus throwing away 4.6E+20 kg of atmosphere is totally unnecessary by better than a factor of 2 - yet it gets trotted out every time this discussion comes up! And on a Physics board!

Chronos

Within the context of what WAS said, utilization of the excess atmospheric mass was clearly intended. My unfortunate use of the term 'venting' obviously derailed the point - it is more efficient to make use of what is already present while minimizing import of what is not. Liquid CO2 can be combined with Hydrogen in a pressurized reactor to produce Carbon, Oxygen, and Water: 2H+CO2 = C+O+H2O. This reaction also occurs when CO2 is sequestered underground on earth. Over tine, the CO2 combines naturally with hydrogen in the rocks. Of course, it is unknown if venusian rocks contain enough hydrogen for sequesterization to be effective on a planetary scale. A substantial quantity of hydrogen would probably need to be imported.

qraal

Well I agree in that sense of what you said. What about reacting the CO2 with oxides to make carbonates?