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The Hegemony has long looked upon Ganymede as a prime terraforming project for humanity.

The Hegemony has the tech for large scale space production so large mirrors or sun shades are able to be built if necessary. They also have gases and materials from the inner planets to aid the project (ex: Venus).

Is terraforming Ganymede even possible and if it is what would be the best methods to attempt? I heard it would become some sort of island world when terraformed.

Note: The Hegemony is looking for a habitual Ganymede where without much equipment humans could survive in it's surface.

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    $\begingroup$ What exactly do you mean by that? I personally believe that no terraforming is possible period (comments are not the place), others believe in it firmly. But maybe if you would elaborate on the following things: a) what would the end result be b) what would your method be for an easier case according to you, you mentioned Venus for example. c) What do you mean by "best method"? d) Why even try? I am serious with this point, imo the biggest issue with terraforming is that it's just a way more complicated way to build a space station. Things are only possible if people are willing to do them $\endgroup$ – Raditz_35 Aug 1 '18 at 12:09
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    $\begingroup$ I think if you were talking about adding life to a barren planet or generating atmosphere from elements already present in the planet, I could see that. Raising the temperature significantly on an ice moon would require a serious amount of energy, enough so that with that energy, you could have terriformed three earth-like planets instead. $\endgroup$ – Neil Aug 1 '18 at 12:18
  • $\begingroup$ @Raditz. A: edited question. B: A shell world or ring colony would be a nice start to getting better at terraforming. C: Some methods probably work but would take ages while others are quick and possibly dangerous. D: Terraforming I feel would make colonist feel safe and secure as well as offering "A new earth" $\endgroup$ – Celestial Dragon Emperor Aug 1 '18 at 12:34
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    $\begingroup$ "We know both too much and too little to talk coherently about what makes a planet habitable" - Larry Niven on terraforming, at this stage terraforming is not a science that we can make well educated guesses about. $\endgroup$ – Ash Aug 1 '18 at 12:39
  • $\begingroup$ This question has a lot of info about how feasible a habitable moon around a gas giant is. I only skimmed it so I may be wrong, but it seems like Ganymede might be too small to permanently hold water vapor but otherwise should be possible to terraform. However, as other people have said we really have no idea how feasible terraforming anything is until we've tried it out on a few planets in real life. $\endgroup$ – Giter Aug 1 '18 at 12:56
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If you really want to terraform a world like Ganymede, you will need to go very big indeed. LDutch's answer provides the context, but where are we going to get the energy to heat the moon, especially when you are so far from the Sun?

I'm going to suggest a laser, but not just some piddly little gigawatt thing orbiting Mercury, but actively engaging the Solar photosphere in order to use it as a lasing medium. (Note, there was an article called "Constructing artificial laser stars" by John Talbot, but this seems to have vanished from the Internet). Simply put, the plasma environment of the photosphere makes for a powerful lasing medium, so a "starter" laser to create a population inversion can trigger a massive, terawatt laser pulse. Ringing the Sun with mirrors to create a circular "racetrack" for the laser pulse gives the medium far more material to lase, and at the appropriate time, one of the mirrors can be manipulated to allow the beam to exit.

From the article:

  1. Orbiting Mirrors

The mirror method would extract laser energy by creating a resonant cavity in which the radiation would make multiple passes dramatically increasing the effective gain. The path would ideally be perpendicular to any velocity gradient in order to reduce Doppler smearing and increase coherence and thus directivity. The laser beam is emitted tangential to the surface of the star.

Sherwood (1988) described a platoon of orbital mirrors around mars or venus to extract a coherent and directed CO2 laser beam from the gain medium. He foresees the use as means of transmitting/propagating our entire culture to a future nano-civilisation established in various other solar systems throughout our galactic neighborhood.

Mirrors external to the stellar atmosphere would reduce the problems of erosion and orbital deflection by the violent and corrosive stellar winds. Although pairs of mirrors would be ideal to extract directed energy from the gain medium, there are power limitations due to the finite reflectivity of the mirrors (which absorb a small but damaging fraction of the radiation). To overcome this problem larger mirrors could be constructed to distribute the heat load, and reduce the Airy diffraction pattern (beam divergence). However large mirrors are extremely vulnerable to orbital debris such as an encounter with a handful of sand from an intersecting orbit etc...

Large mirrors will act like solar sails, this side-effect could be used to maintain a stationary satellite (statite) over the desired location near the solar limb. (see papers on 'statites' by R.L. Forward) The photon pressure from the laser photons and the photosphere could be adjusted to exactly compensate for the solar gravitational force and prevent the hovering statite from falling onto the star's surface. Conservation of momentum would impart a momentum of 2p every time a photon bounced off the mirror. For a multiple pass optical cavity the photon travels back and forth many times stimulating emissions at every pass. The force on the mirrors from this photon pressure in combination from the photon pressure from the star's photosphere acts like a solar sail and can be designed to exactly balance the inward gravitational force pulling the mirror onto the star. These three counterbalancing forces could be harnessed to maintain the mirror stationary against the gravitational pull of the star. ('statites' or stationary satellites by R.L.Forward). Very near the star there may be deviation from 1 over r squared law by dilution of radiation effect of finite angular width of solar disk.

If more than two mirrors are used a ring laser could be produced, the radiation would make numerous quasi-circular trips around the sun; in other words, a photon merry-go-round spinning at the speed of light !

The other thing you will need is a series of mirrors out of the plane of the ecliptic in order to steer the beam, since the motion of Jupiter as it orbits the Sun and the orbit of Ganymede will mean the beam needs to be actively controlled at all times.

This principle can be extended throughout the Solar system, and the beam used as a high quality energy source deep into the Oort cloud if desired.

As for the target, the intense energy from the beam will be defocused somewhat by the targeting mirror(s), likely hovering above the Jovian pole, and steered much like solar sails using the laser energy. Since the builders have so much energy at their disposal, they can indulge in all kinds of exotic engineering projects, but the most likely one would be to simply create a huge "balloon" for Ganymede to be enclosed in. This would help diffuse the laser light, trap the heat and atmosphere and provide some fine control for the project managers on the surface (for example, if the laser is turned off for a short time for maintenance, or to realign the beam with another mirror, the heat energy and gasses remain trapped inside the balloon structure).

Frankly, if you are going to terraform or use super science, then you really need to go "big" with your plans.

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Google is your friend, if you use it.

Terraforming means modifying the atmosphere and surface conditions of a planetoid to make it a similar environment to Earth and even potentially habitable by humans. It is possible to do this to Ganymede but the result might not be a nice place to live or not possible with our current level of technology.

Let's take a look at Ganymede: it is a moon of Jupiter that is bigger than Mercury (although it doesn't have the same mass as Mercury) meaning that it can hold on to an atmosphere. It doesn't have enough gravity to hold on to an atmosphere with Earth pressure, but it would take thousands, if not tens of thousands of years to fade away so we could easily "top up" the atmosphere in the mean time.

Ganymede is also in possession of a magnetic field which is of a huge benefit because it means that Ganymede can deflect the solar wind from the atmosphere, slowing the rate at which the atmosphere will blow away and reduces that radiation exposure on the surface of the moon.

The first step of terraforming Ganymede would have to be by increasing its surface temperature. We could do this through a combination of heating and greenhouse gases. Powerful greenhouse gases such as ammonia (which would also add nitrogen to the atmosphere), nitrogen triflouride and sulphur hexafluoride. The extra heat could be added through solar mirrors, nuclear detonations and or redirecting asteroids to impact the surface. Nitrogen could be added from Titan which is near by to act as a buffer gas and oxygen could be generated through electrolysis of the water ice on Ganymede.

The resulting atmosphere would be thick and would likely have an active hydrological cycle. A thick atmosphere would also provide circulation and help to reduce the temperature differential between the day and night side of the planet.

Ganymede is thought to be made primarily of water-ice and there is even thought to be a subterranean sea beneath its crust between the mantle and the core. This means that when Ganymede is terrafoprmed there would be oceans but it is unknown how large the landmasses would be or if there would be any at all. If there is too little landmass then more can potentially be added by redirecting asteroids to impact the surface.

The resulting Ganymede would still be a very cold palace to live and it would likely be an ocean world with ice at the poles and mostly ocean everywhere else with possibly a few small land masses. It is very unlikely that crops or other forms of vegetation could be grown on the surface due to lack of surface soil so most food would likely have to be provided through artificial means such as hydroponics.

However another way Ganymede could be terraformed is through para-terraforming which involved building several small, or possibly a single giant enclosed shell across the surface of the entire world. This would solve the power of the atmosphere escaping over time and would likely be artificially lit and heated through nuclear power as it is unlikely solar could work at that distance from the Sun. Para-terraforming is currently beyond our current technological ability, much like terraforming although it could be done.

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