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I have seen many people talk about terraforming Venus or Mars. How about Mercury? There is probably plenty of sun light there and I imagine that people could place a magnetic ring at the L1 point to stop solar radiation like they want to do with Mars. How can we make Mercury like a second Earth?

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    $\begingroup$ The reason we always talk about mars and venus is that they're moderately reasonable planets to try it on. $\endgroup$ Commented Apr 12 at 16:02
  • $\begingroup$ Note that Does it even make sense to talk about Mercury's triangular libration points also addresses L1-L5 generally in the answers. Sun-Mercury L1 may not be a useful place to try to put anything because of how much influence Venus has. $\endgroup$
    – Erin Anne
    Commented Apr 12 at 20:11
  • $\begingroup$ Probably easier to move Ceres than to terraform Mercury. $\endgroup$ Commented Apr 12 at 20:30
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    $\begingroup$ Personally, I would build a train track in a circle around one of the poles, and drive it slowly (59 days per cycle) following the sunset. Local temperature can be chosen to be comfortable by how far behind the sunset you drive, since the surface cools from :very hot to very cold. I would get power from a separate train ahead of me that had photovoltaics (perhaps on towers) that still caught sunlight, or by a Stirling engine powered by radiant heat from the surface re-radiated to space. Since we'd be in the "comfort zone" normal windows would give us an ever-changing view of the landscape. $\endgroup$
    – uhoh
    Commented Apr 13 at 2:51
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    $\begingroup$ @uhoh such a train-city (Terminator) is in Kim Stanley Robinson's 2312, but motive power for it is derived from the thermal expansion of the rails behind it. Good book. $\endgroup$
    – Erin Anne
    Commented Apr 13 at 20:32

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Trying to terraform Mercury is not impossible, just extremely impractical. It's close proximity to the sun causes a large number of complications:

  1. Mercury's magnetic field is very weak, the solar wind will strip any atmosphere away
  2. The delta v costs of getting to Mercury are very significant, because you have to slow down a lot to get that close to the sun. The delta-v costs to move an object from the asteroid belt to Mercury is double what it would take to move an object to Mars
  3. The intense heat would cause significant problems getting terraforming materials to Mercury. Much of what you would need is water and cryogenically frozen gases, without protection these cargoes would be blasted long before reaching their destination. Shielding would mean significant weight, and therefore a great deal of cost

Add to that it's far too hot to survive, and the force of gravity isn't strong enough to hold an atmosphere. It's not a good choice.

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Don't even bother trying to think about it.

Mercury is very close to the Sun. A solar day on Mercury last 178 Earth days.

This means that one side of Mercury will remain in sunlight for one Mercurian year of 88 Earth days; while during the next orbit, that side will be in darkness all the time until the next sunrise after another 88 Earth days.

If you are desperate to terraform a planet consider Mars, or better still, don't mess up Earth.

The trouble with this is the equatorial temperatures on Mercury are either too hot or too cold. On the sunny side of Mercury, the temperature will be 420 °C, nearly as hot as Venus, while on the other side (the night side) the temperature will be -170 °C.

The only hope for a reasonable temperature on Mercury is a narrow strip at the poles.

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    $\begingroup$ But how about orbital mirrors? I bet you could get some temperature control with that $\endgroup$
    – Divinator
    Commented Apr 12 at 10:17
  • $\begingroup$ And then what? You're talking about extreme measures just to get a barely reasonable temperature, and you haven't even started thinking about where to get air and water from. $\endgroup$ Commented Apr 12 at 16:04
  • $\begingroup$ @DarthPseudonym Well, I have thought of it, but I didn’t mention it in the comments because this answer said it isn’t possible to address the temperature expect at the poles and that is why I mentioned orbital mirrors $\endgroup$
    – Divinator
    Commented Apr 12 at 16:11
  • $\begingroup$ My point is that "just put in some giant orbital mirrors" is a fantastically huge project to undertake before you can even get around to the necessities of life. And there's not really a local source for water so you'd have to import it all. $\endgroup$ Commented Apr 12 at 16:20
  • $\begingroup$ @DarthPseudonym Yes, the water can come from asteroids or maybe Europa. I bet orbital rings or sky hooks will make the job easier. If you want to write an answer do so. But I don’t need to explain how to terraform Mercury in the comments, when my question is how to terraform Mercury $\endgroup$
    – Divinator
    Commented Apr 12 at 16:25
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Terraforming Mercury would be practically impossible unless we're talking about domeing the planet over, which is often called "paraterraforming" or "worldhousing". Plus, with the exception of needing extra space (which quite frankly could be better done by building spacesteads [think O'Neill cylinders, Stanford toruses and the like]), Mercury is highly unlikely to ever have a large population. With the exception of small skeleton crews working in Mercury's mines, few people will likely want to live on that planet, so building large habitat settlements, let alone trying to make Mercury habitable, wouldn't be that useful.

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  • $\begingroup$ Is there anything worth facing the challenges of shipping it out from a mine on mercury? A quick look at a DV map suggests getting goods from Mercury to Earth is more than Earth surface to Earth, both much more expensive than moon. Also note the question is 'how' - if glass housing mercury, is there enough oxygen and nitrogen locked in chemistry to actually fill one or has it all been blown away? $\endgroup$ Commented Apr 18 at 13:15
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This is an insightful question that I don't think anyone thought to consider before. After all, Mercury is so hot!

The first step would be to build a solar shade to get the right average amount of sunlight to fall on Mercury, protect it from the solar wind, and create a suitable diurnal cycle. This part would represent a small portion of the overall planetary terraforming budget.

After that, a terraforming project will need lots of energy. Most planets have quite a bit of hydrogen, oxygen, and nitrogen bound up within their minerals. If this holds true for Mercury, it should be possible to create an atmosphere, hydrosphere, and materials for soil by mining and processing these minerals. Because there is more solar flux at Mercury than, say, near Mars, the mineral processing on Mercury could progress relatively quickly.

Venus would be harder to terraform both because it's bigger and because sequestering most of Venus's atmosphere into its lithosphere will probably involve more processing work than extracting an atmosphere and hydrosphere from Mercury's lithosphere.

In a terraforming contest between Mercury, Venus, and Mars, I suspect that Mercury might even be first to the finish line.

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