Which of the Galilean moons could we Terraform, and why?

[Spaceception]

Which Galilean moon would be best for Terraforming, and how? Btw, I'm not being strict, the atmosphere only needs to be thick enough so you don't need a pressure suit, and the temperature just needs to be high enough so you only need warm clothing (Winter clothing you'd wear in the pacific NW, and an oxygen mask.

Discuss, and please stay on the topic of Terraforming

 

Edited February 21, 2016 by Spaceception

[_Augustus_]

Callisto. Io and Europa are too irradiated, and Ganymede is still pretty bad.

[Spaceception]

2 minutes ago, _Augustus_ said:

Callisto. Io and Europa are too irradiated, and Ganymede is still pretty bad.

Quote from the Wikipedia article:

Quote

Due to its distance from Jupiter's powerful radiation belt, Callisto is subject to only 0.01 rem a day.

Which is perfectly fine for Humans.

Source

[_Augustus_]

Just now, Spaceception said:

Quote from the Wikipedia article:

Which is perfectly fine for Humans.

Source

Which is why I said Callisto is the best.

[Spaceception]

Just now, _Augustus_ said:

Which is why I said Callisto is the best.

Oh, I thought the '.' was a ',' My bad

[peadar1987]

Callisto actually has the lowest dose rates:

Edit: I also read the full stop as a comma. There is an error in earth's value as well, it is ten times lower than shown here

 

Edited February 21, 2016 by peadar1987

[Spaceception]

7 minutes ago, _Augustus_ said:

Callisto. Io and Europa are too irradiated, and Ganymede is still pretty bad.

 

1 minute ago, peadar1987 said:

Callisto actually has the lowest dose rates:

 

Alright, how would you two Terraform Callisto then?

[Spaceception]

I 'Terraformed' Callisto in US2 by doubleing its day/night cycle from 16 days (Tidally locked) to 8 days, and gave it a weak magnetic field of 0.01 Gauss to protect it from the little radiation it gets, and by giving it an atmosphere of 1.27 Atm. Also, the Temperature rose to -8.5 c (16 f)

[Findthepin1]

I don't think any of them are terraformable.

[sevenperforce]

We can terraform by flinging asteroids at it, or by introducing genetically modified microbes to convert the atmosphere, or by putting big mirrors in orbit to increase irradiation. Any other tactics? Would we be able to have any useful effects with gigaton-class thermonuclear bombardment?

Von Neumann machines are tricky to build, and biological Von Neumann machines (microbes) are unpredictable. 

[peadar1987]

Just now, Spaceception said:

 

Alright, how would you two Terraform Callisto then?

Well it's mostly water ice and rock, so you'd need a huge amount of gas. Your criteria require something that's common, noncorrosive and an extremely powerful greenhouse gas. It should also be readily available in the outer solar system, you don't want to be shifting large amounts of mass around the place.

From this page: https://en.wikipedia.org/wiki/Global_warming_potential I'm thinking your best bet is probably Nitrous Oxide: https://en.wikipedia.org/wiki/Nitrous_oxide. Boiling point of -88 celsius at atmospheric pressure, so should be a vapour at Callisto's surface temperature of roughly -100. Global warming potential of roughly 300 times that of CO₂. Nonflammable, and not particularly corrosive at low enough partial pressures.

The main problem with this would be finding suitable amounts of nitrogen. Oxygen could be cracked from the water of Callisto. Probably your best bet would be to redirect a small Kuiper Belt object, or a Neptune Trojan onto a collision course.

So now some numbers (all data from the excellent Wolfram Alpha: wolframalpha.com). In order to walk outside with no pressure suit, you need about 7% the atmospheric pressure of earth. Atmospheric pressure depends on the weight of the air column above you, which depends on the gravity of the body, so on Callisto, with a surface gravity 12.6% that of earth, you would need a column of air above you with a mass 55% of what you have on earth. Luckily, Callisto has a surface area just 14% of earth, so assuming the atmosphere is thin in comparison with the radius of the moon, it will need an atmosphere with a mass of (0.55*0.14) that the mass of the earth's atmosphere, which gives you 4*10¹⁷kg. You'd only need to import 2/3 of this if you were reacting it with locally sourced oxygen, so you end up with roughly 3*10¹⁷kg. That's a big chunk of ice, but there are probably plenty of them in the Kuiper Belt or at the Trojan points of Uranus and Neptune, and it's only 3 millionths the mass of Callisto itself. Redirecting such a huge thing takes a tremendous amount of energy though. Giving it a kick of just 100m/s, which might be enough to bring gravity assists from Neptune into play, would take 1.5*10²¹ J of energy. To do it over the course of 10 years would require a constant input of 5*10¹³W, or 50TW. Earth's current annual energy consumption is about 16TW.

Once you smash your KBO into Callisto, you drop huge reactors onto the surface to process the atmosphere and the water ice into N₂O and wait for them to do their jobs.

This is a monster of a project, and it's not going to be happening any time soon!

[Emperor of the Titan Squid]

Please explain how and why you would terraform a moon without a cosmic Von Nuimen swiss army knife.

[sevenperforce]

I feel like it would be dramatically easier to move asteroids out of the asteroid belt to a Jovian orbit than it would be to move KBO in.

Hell, aren't there a big swarm of metastable Trojans at Jupiter's Lagrange points? Should only take slight nudges to get a few of them to slingshot each other over to Callisto.

[Bill Phil]

1 hour ago, _Augustus_ said:

Callisto. Io and Europa are too irradiated, and Ganymede is still pretty bad.

Well, we're terraforming, so that would rapidly change Ganymede's  radiation characteristics.

[peadar1987]

3 minutes ago, sevenperforce said:

I feel like it would be dramatically easier to move asteroids out of the asteroid belt to a Jovian orbit than it would be to move KBO in.

Hell, aren't there a big swarm of metastable Trojans at Jupiter's Lagrange points? Should only take slight nudges to get a few of them to slingshot each other over to Callisto.

Yep, but the further in towards the sun you get, the less icy and more rocky the bodies. If you're looking for any old impactor, a Jupiter Trojan would be your best bet. If you want lots of nitrogen, you're going to have to go further out to either Uranus/Neptune Trojans, or KBOs.

The alternative would be to try and mine it from Callisto instead, although that is in itself a mammoth task. The world's largest open pit mine has removed 1.2*10¹²kg of iron ore since operations began in the late 1800s: https://en.wikipedia.org/wiki/Hull%E2%80%93Rust%E2%80%93Mahoning_Open_Pit_Iron_Mine

You'd need 25,000 of these mines to just dig up the mass of the atmosphere you would need. That's before you start to consider how much of what you dig up is actually useful material for producing an atmosphere. I'd be inclined to say doing the job in one go with a massive suitable impactor is the easier of the two options.

[cantab]

Callisto is probably the best bet because it at least doesn't need a radiation shield.

Regarding global warming potential, keep in mind it's defined based on Earth. Many gases are effective warmers on Earth because they "close the window", absorbing wavelengths that carbon dioxide and water vapour let through. Building an atmosphere from scratch the considerations will be different and a mixture of gases will be needed.

More direct, though, is a big lens or mirror in space. There may also be a significant contribution from the waste heat thrown off by whatever machinery is making the atmosphere.

The next question is what is the atmospheric escape like? "Jeans escape" is the loss of gas molecules that are travelling above the escape speed of the body they are on, and so if they are in the exosphere they fly off and never come back. On Earth it is very slow for anything but hydrogen and helium. But on Callisto, supposing an Earth-like exosphere temperature of 1000 K, it will be faster. The full formula is complicated, but it looks like Callisto would lose oxygen a thousand times faster than Earth loses hydrogen. So I think around 100 million tonnes a year will stream off into space.

Doing a little more maths, though, that is only about 1 millionth of the likely total mass of a Callistan atmosphere. So despite the atmosphere being totally unstable on geological timescales, if we can make it then keeping it "topped up" should be trivial.

[Spaceception]

22 minutes ago, Emperor of the Titan Squid said:

Please explain how and why you would terraform a moon without a cosmic Von Nuimen swiss army knife.

Speeding up the rotation to cause friction in the core and create a magnetic field. The best candidate would be Ganymede since it already has a magnetic field.

Although that won't be possible until at least 2250. (IMO)

Edited February 21, 2016 by Spaceception

[peadar1987]

2 minutes ago, Spaceception said:

Speeding up the rotation to cause friction in the core and create a magnetic field. The best candidate would be Ganymede since it already has a magnetic field

Not an option really. To spin Callisto up to 1 revolution per day would take 6.66*10²⁶J. And it's not really rotation that causes a liquid core anyway, it's residual energy of formation and radioactive decay of primordial radioisotopes.

You can add to that that a magnetic field isn't really necessary for much apart from preventing atmospheric escape. This can be mitigated for far less energy expenditure by simply lobbing more mass into the atmosphere from further out in the solar system to replace what you've lost.

[Spaceception]

1 minute ago, peadar1987 said:

Not an option really. To spin Callisto up to 1 revolution per day would take 6.66*10²⁶J. And it's not really rotation that causes a liquid core anyway, it's residual energy of formation and radioactive decay of primordial radioisotopes.

You can add to that that a magnetic field isn't really necessary for much apart from preventing atmospheric escape. This can be mitigated for far less energy expenditure by simply lobbing more mass into the atmosphere from further out in the solar system to replace what you've lost.

Oh. Well do you know of any theoretical possibilities to create a stronger magnetic field on Ganymede?

[peadar1987]

Just now, Spaceception said:

Oh. Well do you know of any theoretical possibilities to create a stronger magnetic field on Ganymede?

It depends what you want the magnetic field for. If it's protection from radiation, the atmosphere is actually a much better barrier. A gamma ray dose will be halved by passing through 150m of air. If it's preventing loss of the atmosphere, it will cost far less energy simply to top up what you've lost.

[Spaceception]

4 minutes ago, peadar1987 said:

It depends what you want the magnetic field for. If it's protection from radiation, the atmosphere is actually a much better barrier. A gamma ray dose will be halved by passing through 150m of air. If it's preventing loss of the atmosphere, it will cost far less energy simply to top up what you've lost.

Oh, then screw the MF

[Exploro]

2 hours ago, Spaceception said:

Which Galilean moon would be best for Terraforming, and how? Btw, I'm not being strict, the atmosphere only needs to be thick enough so you don't need a pressure suit, and the temperature just needs to be high enough so you only need warm clothing (Winter clothing you'd wear in the pacific NW, and an oxygen mask.

Discuss, and please stay on the topic of Terraforming

 

Why would anyone wish to terraform Callisto (or for that matter any Galilean moon) anyway?

Also consider that Callisto may have differentiated geology with liquid water deep underneath its surface (granted not to the extent thought to exist within Ganymede and Europa). I recall reading that signs of such differentiation were detected by the Galileo spacecraft while surveying that moon. Thus where there is likely liquid water, there too is the prospect for life on Callisto. Would we wish to possibly contaminate such an environment?

[Spaceception]

14 minutes ago, Exploro said:

Why would anyone wish to terraform Callisto (or for that matter any Galilean moon) anyway?

Also consider that Callisto may have differentiated geology with liquid water deep underneath its surface (granted not to the extent thought to exist within Ganymede and Europa). I recall reading that signs of such differentiation were detected by the Galileo spacecraft while surveying that moon. Thus where there is likely liquid water, there too is the prospect for life on Callisto. Would we wish to possibly contaminate such an environment?

Well, if we ruled out the possibility of life, then would it be a potential project?

[Exploro]

Which brings me back to the question as to why would such a project be initiated in the first place? Colonization of the surface would be more than satisfactory for our purposes.

[Spaceception]

3 minutes ago, Exploro said:

Which brings me back to the question as to why would such a project be initiated in the first place? Colonization of the surface would be more than satisfactory for our purposes.

Well, it would make surviving easier.