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So, to cut a long story short, a group of people are attempting to turn an earth-sized exoplanet into a new earth; that is, a planet artificially made indistinguishable from old earth.

This planet has no water, and no tectonic activity. Its heavily eroded surface is relatively uniform with no mountain ranges or canyons. Terraforming it will be difficult, but before these people do, they face another challenge: shaping landmasses that resemble those of the old world.

Naturally, any method of shaping the surface of an entire planet to a whim is going to be heinously expensive and energy-demanding, but what would be the most efficient way to sculpt the relatively uniform surface of a planet and produce landmasses that resemble those of earth, albeit superficially?

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    $\begingroup$ How precise do you need to be? You won't get volcanoes, and you won't have the magnetic field (so lots of radiation). None of the geology will be right without an unfathomable level of chemical processing. Granite only forms under pressures many kilometers below the surface. $\endgroup$ Feb 1, 2023 at 18:19
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    $\begingroup$ Lots and lots of gigantic excavators and monstruous haul trucks? $\endgroup$
    – AlexP
    Feb 1, 2023 at 18:25
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    $\begingroup$ What's your goal with this question? We don't know the technology available to the planet builders. Even if we did... @RobertRapplean's point about things underground being just as important can't be ignored. And the result will be a climate that won't match the homeworld at all. So, what's your expectation beyond explosives and giant earth movers? Is there a worldbuilding question here, or is this another storybuilding question? $\endgroup$
    – JBH
    Feb 1, 2023 at 18:29
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    $\begingroup$ Hills, mountains, valleys.. they are all nuisance when it comes to building infrastructure. Why would one spend effort in ruining a planet perfect for building? $\endgroup$
    – L.Dutch
    Feb 1, 2023 at 19:00
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    $\begingroup$ Is there varying terrain elevation? If so, just add water. Otherwise you need to define what you mean my "make a continent". (i.e. Tectonic plate? Large landmass separated from other landmasses by water?) $\endgroup$ Feb 1, 2023 at 19:29

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Prefab veneer puzzle pieces

3-dimensional forms corresponding to the landmasses on earth will be built in space using asteroids as raw materials. These forms (of sizes which are feasible to handle) will then be brought down and assembled like puzzle pieces on the flat ground of this new world. The metallic frames will be covered with soil and rocks, or possibly plastic fake land. Plastic trees might look nice too.

This does not allow for deep oceans (once they bring the water in) . They will be as deep as the edge of the prefab forms.

https://en.wikipedia.org/wiki/Potemkin_village

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Comet Bombardment

This is a quick way to make a whole bunch of pock marks and variation on this exceptionally smooth faced planet. A current and widely accepted theory is that earth had a period of time where it was bombarded with comets, possibly giving earth the water it needed to be the blue marble it is today.

Bonus points here is the potentially small energy requirement: a small "kick" on a comet way out in an outer parts of the system can result in tons of new material coming in. The downside is that you want everyone out of the way and gotta wait a while for the process to run. That is terraforming for you, though!

Targeting some asteroids for bombardment may also help develop long lasting features, like mountains. A "rock" the size of Manhattan will surely work as a mountain.

As craters and debris from the bombardment accumulate, natural variation will occur. Once the planet gets liquid water, the "oceans" will form in the low laying areas while the higher areas will be "continents." The icy comets could be a source of a lot of this water!

What About Internal Magnetic Fields?

This is not going to happen without some crazy science going on here. The least crazy route is likely a kind of "radiation shield" parked at the Lagrange point between the main star and planet in question. This would really be a massive satellite whose full function will be generating a massive magnetic field, deflecting harmful radiation away from the planet.

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    $\begingroup$ Thumbs up. You just need to be careful with bombardment not to turn the surface to molten lava. It takes a very long time for such things to cool to habitable temperatures. $\endgroup$
    – Boba Fit
    Feb 1, 2023 at 20:17
  • $\begingroup$ Landing an asteroid, even one that's a single solid rock, gently enough to leave a mountain rather than a crater, is tricky and expensive. It's going to have to be braked all the way and soft-landed. If you let it fall freely, you just get a crater. $\endgroup$ Feb 2, 2023 at 0:34
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    $\begingroup$ This wont be making the old earth continents right? $\endgroup$
    – Demigan
    Feb 2, 2023 at 9:14
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The planet is spinning. There is a star nearby. Just add a big mirror and you have a huge photoablation lathe.

You need a bunch of satellites in sun-synchronous orbit around the planet. Each should have a large, steerable mirror. Focus the sunlight reflection from a group of satellites to a point that should be lower, and the rock will start to vaporize.

The method is scalable and all energy needed can be had from the star. Just keep producing enough satellites and eventually the job is done.

Now one complication is where the vaporized rock will end up? It will mostly condense into small dust particles, that will land in random places. By using a slightly less intense beam, you can melt the dust together to grow mountains.

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Step 1: Start over

Re-melt the planet, how? not important, probably a lot of nukes or asteroids; melt it down to a liquid sea of magma, then let it cool (you also get a magnetic field from a newly liquid core)

If you're lucky, the crust will eventually be the same consistency as air-dry clay, allowing you to mold the planet's surface to whatever you want.

if you're willing to play the long game, wait a few million years and let tectonics do your job for you, dump some water on the surface too to help cool down the planet and for some oceans

Step 2: enjoy :)

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  • $\begingroup$ > crust will eventually be the same consistency as air-dry clay It'll be the same consistency as igneous rock... > Re-melt the planet That requires truly astronomical amounts of energy, even for a group powerful enough to terraform a planet... $\endgroup$
    – neph
    Feb 3, 2023 at 4:03
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I know this is a complete troll answer - but you call up the planet of Magrathea and ask for Slartibartfast.

(Those who know, know)

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Start with Australia

It's small, it's mostly flat, it's mostly featureless.

QA might not notice mistakes in Zealandia

If you want a no consequence practice run at making mountains, you can try Zealandia, the undersea continent that New Zealand and New Caledonia sit on. If Kelly from QA pays a site visit, it won't be as obvious that you made a mountain half the height it should be and 400 km's to the west.

She'll get you from the documentation in the end, but it might be after completion, or after the client has had beneficial usage. Better to ask for forgiveness than permission.

Especially if the permission is from Kelly and forgiveness is not.

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You don't mention any moons or gravitational effects, so I'll go ahead and assume you don't have any. You sort of need some sort of rotational activity otherwise you don't have days. There'd have to be a magnetosphere or else you won't hold on to any atmosphere. All that means that you don't have tides, and may not have seasons (unless you have a "wobble"). That's all going to have profound effects on your weather systems.

New Earth is currently roughly smooth and featureless. You're going to have to dig out the Mariana trench, and dump the material onto somewhere you want land mass. You're going to have to scrape up enough material from just about everywhere to make Everest and all the Himalayan mountain range. And so the list goes on.

Instead of all that, go cheap. Start by ground-working a load of levees by scraping up material in what will be the ocean and making "soil walls" where the edges of the land will be. Now get out your galactic hose pipe and start filling up the oceans with water.

At some point, some of that water will evaporate and will be carried by the atmosphere to some other location, where it will fall as precipitation. You've now got a puddle on a bit of the planet where land was supposed to go. You can now scrape out rivers and lakes and let that water fill those spaces. Water left sitting still will start to stagnate though, so you can throw in a pump or two to make it flow, and empty out over the top of your levees back into the seas.

At some point someone's going to want to build an earth bank in their back garden. Soil can be obtained by digging out a river (if one is required), or by digging out the ocean. You could even pre-prepare by having "soil mines" in the middle of the oceans (remember, they're uniform depth, so the mines can have levees around them like the land mass does). If someone wants soil, they mine it from the middle of the ocean and bring it back to wherever they live. Sure, it costs a bit to do, but essentially you've pushed the cost to someone else rather than the original terraformers.

I'll admit you're really creating Theme Park New Earth, rather than one completely indistinguishable from the original. I said it was cheap, not perfect! I guess over the next 200 years, you might have mined enough of the soil from the oceans to have got the depth required, and the necessary material to make hills and mountains too, but by then the original terraformers will be long since departed leaving their descendants to do the work they avoided all those years ago.

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