Quantimez said:You provided good points in many areas, and you are very right in so many points. Though one underlining theme may present itself as it does today. Economically speaking cost. Also not meaning to appear pessimistic. You would have to operate carefully in a vacuum and every member working there would need protection against a variety of things while the construct these things factoring in tourism. Titan was used as an example that though it had low G relatively small size and mass its components could exist in those tmperatues in some form(Nitrogen, methane, ethane etc.) Though water vapor and CO2 would not. These are green house gases to Earth's atmosphere trapping heat. Your right Titan gets minimal light. Though Jupiter being estimated 5.2 AU Ganymede may receive just enough heat and warmth 19% of Earth. You would just have to keep it "lit" from refreezing then implying more green house gases. Perhaps after global thermonuclear detonations. You can still use solar panels at that distance and comets become active and at that distance as well underlining the possibility. The Earth's atmosphere has less than 1% of CO2 and perhaps other trace green housegases and see what it has done?!? Once oxygen splits from hydrogen in the vast amounts of water ice on ganymede. Then vaporize naturally (O3 ozone) from radiation as easily as it forms from ionizing electrical arcs on earth. Now a vacuum makes sense for space travel but in a sense of priority of pace tourism and manufacture it seems easier and a bit more cost effective to have an Earth like biosphere for relaxation looking up into the jovian sky and for working on building those materials needed further out as a refreshing nostalgic waystation. The gravity would be similar to the moon already imagine how easy would(hypothetically) for the apollo astronauts without those"bulky but light already in lunar gravitation). As landing on the moon was a fearfully but time consuming maybe and maybe not but it was indeed possible. We came from figuring out how to get into orbit toward the moon in 8 years factoring in cost. Optimistically speaking, we don't know until we try it's a maybe so or maybe not. The impossibles of yesterday are proving possible today. Mars has water ice? Short liquid flows? Before it was thought only CO2 ice existed and it's GRAV was to low to hold a thick atmosphere and a no magnetic field. Venus has no magnetic field look at it's atmosphere! Those assumptions indeed contradicted what exists in our solar system. In all confidence may I imply that its highly beneficial to terraform at minimum Mars and a moon in the Jovian system Ganymede to make to bring things from home to makes the voyage more comfortable and reasuring. Nothing great ever strived and worked for was easy. There's nothing like a blue sky for the heart.
cjameshuff said:What precisely in its composition makes you think it could build the sort of thick nitrogen atmosphere you'd need? You're looking for an Earth-atmosphere-mass of nitrogen in something that's mostly rock and water. There might be some ammonia there, but its presence is mostly speculation. "far greater abundance than required" of what, and how do you know this?
That's not logic, it's just bad math. You don't get to simplify inverse square falloff to simple inverse falloff...that certainly isn't going to "diminish the likelyhood of error". Mars is about 1.5 times Earth's distance from the sun (not "a little more than twice"), which does work out to very close to 1/2 the sunlight per unit area. Venus, at about 0.7 AU, gets twice the sunlight. Jupiter and its moons are 5-5.5 times the distance, which means it gets 1/25-1/30th...as I've said multiple times, 3-4%. For Jupiter, not Saturn...once again, Saturn and its moons would get around 1% of what Earth does...which is why Titan's cold enough to retain its atmosphere, despite having one full of methane and other greenhouse gases. Your estimates of the difficulty involved are wildly off because you're not even using the right scaling laws.
This is ignoring what would be blocked by the thousand-km-deep atmosphere you'd need to have Earthlike pressures at the surface, and you've said nothing about how you'll get around the issue of atmospheric loss. You can't just ignore inconvenient problems.
Saturn V said:You forgot to add wator vapor, though it is a variable it still counts as a greenhouse gas. Indeed water vapor plays a big role in the system so water vapor and CO2 may go hand in hand for Earth's atmosphere and keeping it stable.
jarednjames said:I've just spent 30 minutes reading through this lot and I really wish I hadn't.
Quantimez, you clearly don't understand the basics of the maths and concepts behind simple issues (such as sunlight and atmospheric conditions) and yet you are making wild claims regarding energy and compositional makeup of these bodies.
You also don't appear to have a solid understanding of the economic side of things and are again making rather wild and extremely speculative claims regarding the justifications for such tasks (terraforming).
sophiecentaur said:Is terraforming an answer to anything?
Hydrogen Greenhouse Planets Beyond the Habitable Zone
Raymond Pierrehumbert, Eric Gaidos
(Submitted on 29 Apr 2011)
We show that collision-induced absorption allows molecular hydrogen to act as an incondensible greenhouse gas, and that bars or tens of bars of primordial H2-He mixtures can maintain surface temperatures above the freezing point of water well beyond the "classical" habitable zone defined for CO2 greenhouse atmospheres. Using a 1-D radiative-convective model we find that 40 bars of pure H2 on a 3 Earth-mass planet can maintain a surface temperature of 280K out to 1.5AU from an early-type M dwarf star and 10 AU from a G-type star. Neglecting the effects of clouds and of gaseous absorbers besides H2, the flux at the surface would be sufficient for photosynthesis by cyanobacteria (in the G star case) or anoxygenic phototrophs (in the M star case). We argue that primordial atmospheres of one to several hundred bars of H2-He are possible, and use a model of hydrogen escape to show that such atmospheres are likely to persist further than 1.5 AU from M stars, and 2 AU from G stars, assuming these planets have protecting magnetic fields. We predict that the microlensing planet OGLE-05-390L could have retained a H2-He atmosphere and be habitable at ~2.6 AU from its host M star.
qraal said:To tie this discussion to engineering let's look at the physical requirements of the task of providing Ganymede with 10 bars of hydrogen atmosphere. The radius is 2634.1 km and surface gravity is 1.428 m/s2, letting us compute the total mass of atmosphere as 6.1E+19 kg. Sourcing that much hydrogen from the gas giants will be challenging, but not ludicrous in the context of a solar system wide economy. Of course we're a long way from that point as yet.
The question for would be terraformers of the gas giant Moons is just what to do about the ice? The outer Galileans and Titan are half ice, implying very deep oceans if they fully melted. The obvious answer is to keep their average temperature sub-glacial, but then the Moons aren't much better than the Antarctic ice-caps as habitats and a lot further away.
cjameshuff said:You're nowhere near to the point where the ice can become a problem.
Your assumption that the entire mass of the atmosphere would be subject to the surface gravity of the moon is wildly wrong. The more you pile on, the further out of the gravity well it extends and the less the atmosphere you're piling on contributes to the surface pressure.