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An alien entity fell in love with Earth a long time ago. When he came back to her, she looked different. He would like to return Earth to her Hadean eon when she was much hotter.

This entity has abilities that are comparable to what we suspect a Kardashev Type 2 civilization would be capable of.

The entity would like to return Earth to the Hadean eon without having to throw tons of rocks at her or changing her composition. And he doesn't want to use a Mega bomb if it isn't necessary. A bomb can be used, but he wants to make sure that Earth doesn't lose too much weight in the process. Any loss bigger than 1% will be noticed.

The time and energy spent to bring her back is irrevelant, but the sooner the better.

How can I make the Earth red again?

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    $\begingroup$ Try using large mirrors tuned to the infrared reflecting more of the suns light at earth heating it up $\endgroup$ – Ummdustry Apr 6 '18 at 9:39
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    $\begingroup$ Do you want it just red, or glowing hot? $\endgroup$ – L.Dutch Apr 6 '18 at 9:44
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    $\begingroup$ Kardashev Type 2 are the guys that are able to build dyson spheres. Building an oven around earth to heat it up will be an accomplishable task for them. Producing heat is among the easiest things in the universe $\endgroup$ – Raditz_35 Apr 6 '18 at 10:56
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    $\begingroup$ @Raditz_35 I ve just checked he has no planet cooking book. Will the temp be enought to have a well mixed lava ball. May you share the oven configuration ? Preheat the oven to what temp? $\endgroup$ – Drag and Drop Apr 6 '18 at 11:21
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    $\begingroup$ Did this alien try extracting all the hydrocarbon chains under the ground and tricking the humans on the surface to burn those hydrocarbons as a source of fuel? Because it's working. $\endgroup$ – corsiKa Apr 6 '18 at 14:47
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Buy a lot of paint. Presumably a Type 2 Kardashev civilization entity can lift a bucket that large...

enter image description here

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    $\begingroup$ And few led for a glowing effect? $\endgroup$ – Drag and Drop Apr 6 '18 at 13:44
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    $\begingroup$ I always found that to be a weird logo. Cover the Earth in paint? No thanks, that sounds pretty hazardous to my health. $\endgroup$ – kingledion Apr 6 '18 at 14:22
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    $\begingroup$ @kingledion nah it's cool, their paints are lead-free and low VOC. $\endgroup$ – Harper Apr 6 '18 at 15:01
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    $\begingroup$ upvote for the relevant logo $\endgroup$ – spacetyper Apr 6 '18 at 16:12
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    $\begingroup$ You deserve an internet. $\endgroup$ – Renan Apr 7 '18 at 1:39
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Actually a very interesting premise - a type 2 Kardashev civilisation entity would have command over significant assets, but I believe also in the nano scale as well as the macro scale.

Hence it would probably be a good bet that it has an unbelievablely large arsenal of nanobots at his command.

The cloud of nanobots would be able to make large structures as well as small, and change the configuration of the environment too. Indeed, to capture the energy of the sun, one needs means to create large structures without the need to think, design, or manually make them - hence AI controlled nanorobots would be one of the likely scenarios, ones which could manipulate large amounts of material.

These nanobots can then be sent to earth, to 'reconfigure it into a new matrix'. Basically, the Hadean Earth has high temperatures, high atmospheric pressure, and high levels of C02 - these can be achieved by the nanobots by first self-replicating, then disassembling the crust, ejecting the material into the atmosphere, boiling the oceans, and releasing the magma.

The entity can then blissfully come down and admire his handiwork.

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    $\begingroup$ Remember, though, that even Kardashev-II self-replicating nanobots can't make energy out of nothing (presumably)- the extra energy difference between "present Earth" and "Hadean-like Earth" will still have to come from somewhere. $\endgroup$ – Maxander Apr 6 '18 at 15:33
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Impacts are your friends

Step 1:

Push the moon towards the Earth. Once the moon gets to ~20,000 km from the Earth, Earth's gravity will cause it to disintegrate into a ring.

Step 2:

Perturb the ring. I think that many of the moon particles will end up impacting Earth anyways, but a little perturbation won't hurt. Get those particles into nice elliptical orbits and then atmospheric drag will eventually get most of them to impact the Earth's surface. Remember, as the oceans vaporize, you will only get more atmosphere to help drag down moon particles!

Step 3:

Wait for the Earth to heat up. There is over 7e22 kg of moon. The potential energy of dropping those from ~20,000 km is something on the order of 1e30 J. That is a million years of sunlight energy that strikes the Earth. If you can deliver all that energy within few hundred years, it should be not problem to vaporize the oceans and get the Earth's crust nice and glowing again.

Note: The best part about this is that there is no way you will lose 1% of the Earth's mass, since by tossing a moon down there, you will be gaining about 1% of Earth's mass! Even if you blast a few impact particles off into deep space, they will be more than made up for.

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    $\begingroup$ It might be worth considering that when the Earth was "nice and red" the moon may not have separated from Earth yet. This method would actually restore Earth to it's original size. $\endgroup$ – Jason Apr 6 '18 at 20:48
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    $\begingroup$ @Jason: it is currently believed that it was a mars sized planet that collided another one, giving a larger body we today name Earth, and a smaller one named the Moon. The Hadean Earth was after that event, so the size was equivalent to today. $\endgroup$ – aluriak Apr 6 '18 at 21:16
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Spread a lot of Fe2O3 (iron oxide) all over the planet.

Where there is no water it will give a nice red appearance, while where there is water it will make it red.

water contaminated by rust

At the end Mars is known as the red planet just for the rust it has on it.

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Hadean Earth was Hadean Earth because it was still cooling down. All the entity has to do is reheating the planet.

A K2 civilization should be able to harness the energy output of a star. The entity can make something akin to a dyson sphere and redirect the energy to Earth.

The atmosphere might be lost to space. But the atmosphere weights only around 5x1018 kg according to the heavier estimates. That is less than one millionth of the mass of the Earth (approximately 6x1024 kg). Surface water will also be lost, but according to Wikipedia, the whole mass of Earth's hydrosphere is around 1.4x1021 kg, which is about 0.023% of the mass of the planet, so your "no more than 1% mass loss" requirement is accounted for.

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  • $\begingroup$ Will we be loosing a lot of elements? May be we could gather the lost and import them back or they won't be able to exist in their know state? $\endgroup$ – Drag and Drop Apr 6 '18 at 13:01
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    $\begingroup$ @DragandDrop the only difference between old Hadean Earth and new Hadean Earth is that the new one is about 1/1000 lighter than the other. We would have lost a lof of hydrogen but we would regain it the same way old Hadean Earth got its surface water: just throw a lot of icy comets over geolocical time. The entity should be able to do that, and in a more gentle way than nature would have it. $\endgroup$ – Renan Apr 6 '18 at 13:09
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    $\begingroup$ The formation of atmosphere and presence of liquid water on Earth is one of the big questions of planet formation. Were they trapped internally (chemically?) as elementally they should be lost by a Hadean Earth until it was cool enough that any trapped could be slowly released, or otherwise deposited by post Hadean comets. Either way your visitor does not expect either to be present anymore, as they were not at the earlier time. $\endgroup$ – Windlepon Apr 6 '18 at 13:15
  • $\begingroup$ Just wanted that information to show that planet composition was the same with this process as those element where not on the old Hadean. Even if Water and atmosphere is still a question ask by the Cool Early Earth kids. $\endgroup$ – Drag and Drop Apr 6 '18 at 13:17
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Which end of the Hadean are you going for? There was the early Hadean with molten surface and a rock vapor atmosphere, and there was the late Hadean with liquid water oceans at a balmy 230C with an atmosphere at around 27kPa.

Early Hadean requires lots of surface heating so the bombardment and radiation ideas are the way to go. A more subtle method of creating the late Hadean would be interior heating.

A Kinder, Gentler Planet Cooker

Alexander already suggested infusing the earth with radioactive elements. If you could deliver a large dose to the core, conduction and convection would take care of the rest. A large critical mass of dense fissile material (and what fissile material isn't dense?) placed on the Earth's surface would naturally find its way to the core with local scarring to the crust and mantle.

Another way to heat from the inside out would be akin to a microwave, or to a Bubblegram. Normal radiation wouldn't make it though the atmosphere very effectively, but bombardment by a focused neutrino emitter could warm the core via Cherenkov radiation and trigger nuclear changes within heavy elements, infusing radioactive material directly into the core. This would require some unknown technologies, like aimable neutrino emitters, and probably neutrino reflectors to get enough interactions.

So, a large high energy neutrino emitter bombarding the planet from a 60 degree spherical cone converging on the core, so that there is relatively low neutrino density on the surface but a small area of extreme bombardment in the core, combined with a reflector reflecting back the same 60 degree cone to increase interactions would bias heat toward the core, gently warming the planet from the inside.

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Infuse Earth with radioactive elements.

This is much less invasive than Dyson spheres, mega-bombs or celestial calamities. Radioactive elements will undergo fission, which will heat up the Earth's mantle and lead to massive volcanism (think Siberian Traps). With half-life of the elements being long enough, this volcanism will turn the Earth back into Hadean era.

However, the whole process will take centuries and millennia to unfold. The idea is actually similar to Asimov's "Robots and Empire". And, even "Kardashev II" level is not needed for it.

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The Greenhouse Effect

There is little chance of modern society turning Earths atmosphere into something like Venus. However, a powerful alien entity would probably be able to do this.

The main ingredient in the Venusian atmosphere is carbon dioxide, not the mere 0.04% concentration that climate change scientists seem so worried about, but 96.5%. The Venusian atmosphere is much heavier too, being 93 times the mass of Earths atmosphere on a slightly smaller planet.

Our strategy is simple. Pick a greenhouse gas, or a combination of greenhouse gasses, and release enormous quantities on Earth.

The amount of solar energy hitting Earth is 174 PW, enough to heat the entire mass of the planet by 1 degree Kelvin in a year or two. So once we set up the correct atmospheric conditions, we can expect the appropriate surface temperature in a reasonable period of time.

Of course, this will heat up the crust but not the core or mantle, as they are already hotter than the temperature you are likely to achieve.

Another issue is that you may as well just enjoy Venus, which already resembles what this would do to Earth, and is not far away.

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Move Earth's Orbit

Switch orbits of Earth and Mercury would probably do the trick. It wouldn't be quick for us (well, our deaths would be fairly quick), but for an entity that visited so long ago, what's a few million more years.

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