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Not necessary to achieve the same level of insolation as on Earth to have earth-like conditions. Actually , hundreds of times less are enough, provided that the balance infalling radiation / reflection, emission is as high that the equilibrium is achieved in normal temperature range for the habitable layer under the optical / infrared surface... also the flux of free energy which to be utilized by the eventual biosphere producers is not necessary to be photonic...
Look again in "Gerald Nordley surface gravity" -- google for it, a .pdf will appear -- Titan...
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Not necessary to achieve the same level of insolation as on Earth to have earth-like conditions. Actually , hundreds of times less are enough, provided that the balance infalling radiation / reflection, emission is as high that the equilibrium is achieved in normal temperature range for the habitable layer under the optical / infrared surface... also the flux of free energy which to be utilized by the eventual biosphere producers is not necessary to be photonic...
Look again in "Gerald Nordley surface gravity" -- google for it, a .pdf will appear -- Titan...
Well terraforming does mean making the planet habitable for humans. I think their may be Earth-sized planets underneath the layers of gases in side Neptune and Uranius. If you increase the light levels on those planets, you could dissappate away some of that hydrogen, thin out the atmosphere and let the heavier gasses remain. I think what you would have left would be a liquid water planet. You would need to provide some floating platform to support the complex life you want to seed there. I heard somewhere that there may be a water ocean underneath the thick atmospheres of Neptune and Uranius. If we could blow away the atmosphere of each planet and heat up the surfaces with giant mirrors, we coule retain the oceans. Of the two, I think Uranius might be the more likely prospect as it is closer to the Sun and its surface gravity is 0.794 times that of Earth. You would probably reduce its diamter by getting rid of its atmosphere, but we are talking about a planet 4 times the diameter of Earth, the price you pay for having such a huge planet with a low density is that its made mostly of water, you would want to float some artificial continents on it. A planet 4 times the size of Earth could have 16 times Earth's surface area if you keep the land to water ratio the same Neptune is another 16 Earths worth of living space if properly terraformed, it is somewhat smaller so you'd need greater land area in proportion to total surface area. Uranius's mearly 90 degree tilt probably doesn't matter too much since the reflective mirror would be providing most of the illumination.
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Tom,
In principle I of course agree with the terraformability of the "ice giant" planets. The only "objections" I have are connected with some "misconceptions" of what is necessary and enough to be done ( i.e. to minimize the work/cost of such effort ).
1. The escape velocity of the ice giants are still high , so it will be very expensive to export off-the gravity wells the hydrogen. It is pointless, too cause the H/He also contribute to the most valuable feature of Uranus and Neptune -- source of right "dose" of static surface gravity. Anything usefull ( as artificial continents ), which could float on liquid rock or liquid water, could float also in H/He+trace gases cryogenic atmosphere... NOT necessary to get rid of the hydrogen and helium. The floating continents could be aerogel-like ( but with vacuum bubbles ) and well-insulating from the surrounding cold. The cold also is resource = better heat sink, higher efficiency of the thermal machines. Not to mention that that much hydrogen / helium would be real treasure after the date we learn how to fuse them into more helium, carbon ... it would be like a ensemlbe of continents floating in a cold star, with enough thermonuclear free energy gradient, thye civilization hundreds of times bigger than ours to thrive there for trillions of years, absolutelly independent from natural EM radiation sources... Not usefull and profitable to expell hydrogen also because the surface gravity being right , one loses usefull surface with loosing planetary mass...
2. The simulations show that Uranus and Neptune are too hot ( i.e. young) and too dry ( relativelly low oxygen, i.e. water content ) to have NOW liquid water oceans in them == perhaps after 5-9 billions of years, yes. The simulations show also that during formation the Solar system most probably may expelled 4 "neptunes" -- cold enough into the interstellar space, so liquid oceans to form into them... but again it is better the floating continents to be higher and colder, than floating over the liquid water lawyer where the temperatrure would be at least hundreds of degrees celsius and the pressure in the range of thousands of bars...
3. Yes, the axial tilt, the orbit, the distance from the central star is irrelevant for the insolation level, if good optics provided -- not necessary to be reflectory one, the study of metasmaterials with negative refractivity, etc. shows that it is better to deal with swarms of trillions and trillions of small "lences" hovering in the planet-solar L1 provided with active position control, focusing characteristicvs, and "hive inteligence" than to put super-giant and super-flimsy mirror ( which btw, could also possess these flexible life-like features, including self -repair, self-power supply, self-regulation ... "telepathically " linked to the new planetary biosphere homeostasis.. )... Using optics we could insolate any body -- up to SEVERAL DOZENS of LIGHT YEARS away from star -- limited by the planetary mass conditionally ... the only thing I`d like to stress on is that indeed our idea of how much light per sq.meter is quite exaggerated by the solar constant here on Earth. 1.5 kWatt is way TOO much. The level of insolation is not the most major factor determining the local temperature... The temperature of one body is fiunction of how much energfy it receives, and how much it releases... with what pace... Neptune and Uranus colonies spawning at dozens of Earth`s areas habitable ~1G well insolated territory actually could live with literrally hundreds of times less light per square meter, than Earth... if we play with the photosynthetic efficiency, even less -- the only aesthetical limit would be the darkening of the landscape -- let me remind that in average living room, where we can read a book, the illumination levels are approximatelly 1-2 watts per square metter...
Perhaps, we must concentrate over the question "What CAN NOT be terraformed?" in this forum?
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