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In a small closed system, like a spacecraft, getting rid of built up heat can pose a problem. One method would be to radiate it into space by first pumping the heat into large panels.

My game takes place on a small planet (unrealistically small, but still bigger than Le Petit Prince) and terraforming is one of the goals. If the planet is cold, a player may want to heat it with whatever heat source they desire, for example by burning (imported, pehaps nuclear) fuel. A more 'external' solution would be to redirect solar radiation to the surface, but I prefer an on-surface solution.

Cooling the planet poses a problem. I've thought of large radiators extending high up but because of practical reasons (they are unsightly and don't fit the screen) I'm looking for alternative solutions here.

My first thought was some sort of system that launches heat cartridges away from the planet. A heat pump would collect heat into a medium (liquid? solid?) and then launch it off away from the planet.

My initial feeling is that this is quite far-fetched and likely not efficient at all. I also have never heard of any such system besides the 'heatsink launcher' in Elite Dangerous.

Even though I'm taking quite some liberty with the small planet size, I'm still hoping to have a solution for heat removal that feels hard-sci-fi-ish enough.

I'd love to hear any ideas if you have any.

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    $\begingroup$ It's hard to imagine a medium that could collect the heat of a planetary-sized object and serve as a vessel for its ejection from the planet... and you'd rapidly run out of material. $\endgroup$
    – jdunlop
    Commented Jan 28, 2021 at 23:07
  • $\begingroup$ Depending on how unrealistically small your planet is, it might be possible to use comets, which are mostly made of ice (albeit not necessarily water ice), for cooling. You could have a gravity gizmo on the surface pull one into the planet. $\endgroup$ Commented Jan 29, 2021 at 1:08
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    $\begingroup$ One problem you'd run into is that, as the planet gets cooler, it will become progressively harder to cool it more. For that reason, something like the albedo, umbrella, or balloon approach seems like a good bet, because it's easier to stop energy from getting to the planet than it is to get rid of heat that has already "landed." $\endgroup$
    – Tom
    Commented Jan 29, 2021 at 2:55
  • $\begingroup$ How small of a planet are we talking? Built up heat doesn't seem like a problem you would even have if it's small enough (and far enough from the star). If it's close enough to the star, well, then you're probably not going to be able to get rid of heat by any means. $\endgroup$
    – spacetyper
    Commented Jan 29, 2021 at 5:53
  • $\begingroup$ The heat launcher reminds me of Bethselamin. No planet, no cooling problem. $\endgroup$ Commented Jan 29, 2021 at 6:45

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Increase the albedo.

The Albedo is the "whiteness" ie. effectiveness (and scattering) of incident light. A planet with a low Albedo will look dark and the surface will heat-up relative to the amount of starlight (sunlight) it gets.

In Earth's case, the Albedo is about 0.9 for snowy areas and 0.04 for Asphalt. The overall Albedo being about 0.3.

Raise the mean Albedo to as near as 1 (perfect reflection of all radiation) and you can cut down on about 1KW of incident radiation from the Sun per square meter. Sure, some will bounce around inside the atmosphere still, but you should be able to create a global Antarctica effect in no time. Aluminised Mylar sheets might just fit the bill, they're cheap and lightweight, but you'd needs lots and lots to cover a significant area.

Edit as per comment below:

If not on the surface, then basic inverted umbrella shapes on columns a few hundred or even a few thousand feet high depending on the scale you need, a bit like this:

enter image description here

Image copyright through bdir.com 2021 (commercial website)

There could even be hundreds or thousands of miles/kilometers between each stand, housing a motorized Sun-tracking system, capable of furling and unfurling upon instruction.

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  • $\begingroup$ I like the idea as it would be an on-surface solution for redirection of incoming heat. The planet can then be its own radiator and cool down. However, since this is for a management-type game, it does pose a new visual problem. Coating the whole planet in some sort of shiny material is not ideal and I'd rather plop down some large machine or installation, hence my first idea (cartridge launcher). $\endgroup$
    – Waarten
    Commented Jan 28, 2021 at 21:51
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    $\begingroup$ +1. You could also increase albedo by seeding additional cloud cover, or by putting mirrors into orbit that would prevent solar radiation from ever hitting the planet. Those aren't ground-based solutions, but the effects would at least be visible as large shadows on the ground. $\endgroup$ Commented Jan 28, 2021 at 21:52
  • $\begingroup$ @Waarten Oh I see the issue now. Following from what N Hoagie said, could giant Mylar umbrellas a few hundred feet above the ground work? They could track the sun's movement (having a motorized control tower at the base) and they'd certainly be visually striking. $\endgroup$ Commented Jan 28, 2021 at 21:54
  • $\begingroup$ @Tantalus'touch. Thanks, I'll see if I can make this work. I feel this approach (and other forms of shade and reflection) is the most solid in terms of realism and feasibility. $\endgroup$
    – Waarten
    Commented Jan 29, 2021 at 10:22
  • $\begingroup$ as a visual for the game, a cloud producing factory could serve. $\endgroup$
    – ths
    Commented Jan 29, 2021 at 10:54
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Melt the ice caps.

Ice requires a huge amount of latent heat in order to melt. That is, as ice melts, it absorbs a great deal of heat energy without actually changing temperature. This is exactly what happens when you put ice into a warm drink - the ice melts, absorbing heat energy from its surroundings. The overall amount of energy in the drink never changes, but you've stored some of the heat energy in breaking the bonds that hold the ice together, resulting in a lower overall temperature.

One could imagine that if we mined the entire polar ice caps and brought them to the equator, the ice would melt and lower the temperature of the surrounding area. Of course, you'd have to be willing to deal the the consequences of melting that much ice, but that might be an interesting challenge in the context you're describing.

Alternatively, you could also bring in ice from off-world to lower the planet's temperature. Capturing or mining an icy comet (a la Futurama, as mentioned in the comments) would allow climate modulation even if the planet has no ice caps, or if they've been melted already.

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    $\begingroup$ That'd definitely work for a quick-fix. $\endgroup$ Commented Jan 28, 2021 at 22:16
  • $\begingroup$ Obligatory Futurama link. $\endgroup$
    – jdunlop
    Commented Jan 28, 2021 at 23:05
  • $\begingroup$ Even though this might not be a long term solution (and we may never create a planet that is 'more icy' than what you started with) I like that this poses some infrastructural challenges (placement of the liquefier, pumping away meltwater) that could be fun to play with. $\endgroup$
    – Waarten
    Commented Jan 29, 2021 at 10:26
  • $\begingroup$ unfortunately melting the ice caps also lowers the planet's albedo, meaning it absorbs heat faster and so this method is self-limiting in its effectiveness, as well as only working as long as you still have ice caps to melt $\endgroup$
    – Tristan
    Commented Jan 29, 2021 at 13:21
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    $\begingroup$ @Tristan True, but the poles receive the least insolation of anywhere on the planet, by their nature of being at the poles. For a planet with no axial tilt, there's virtually no sunlight falling on the poles in the first place (assuming the ice caps don't cover a huge portion of the planet), so the albedo change will have almost no effect. Even on our planet, latitudes >80 only get about 5% of the total global annual insolation. Melting all the ice in a dry location could perhaps increase cloud cover and offset the change in albedo, too. $\endgroup$ Commented Jan 29, 2021 at 14:16
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Build a space umbrella!

One idea suggested a long time ago to possibly terraform Venus is to construct an orbital solar shade in the L1 point to protect Venus from both light and solar radiation. The Solar shades radius would need to be 4x the size of the planet to provide total cover (heave the planet inside the umbria of the solar shade.

Building a solar shade is within the reach of modern technology. Though how you prevent the shade from getting blown about like a solar sail is an issue.


Or you could place trillions of reflective balloons filled with hydrogen into the atmosphere to reflect light away from the surface.


Or you could be giant heat pipes to transport heat from the surface to the upper atmosphere to heat the upper atmosphere which would increase the speed that the planet radiates heat into space.

Alternatively creating giant vortexes to mix warm surface air with cold upper atmospheric air would have the same effect.

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    $\begingroup$ It doesn't matter the size of the planet - big or small you're going to need the same relative % of its available resources to be able to construct a shade of the necessary size. Thus a solar shade at a Lagrange point is far more feasible than a half-planet-sized atmospheric umbrella, as it would use far less material. It also doesn't run into issues with deployment and retraction infrastructure, and as a potential useful hook for a game, would require regular maintenance due to micro-asteroid impacts. Thus, this is the correct answer. $\endgroup$
    – Ian Kemp
    Commented Jan 29, 2021 at 13:28
  • $\begingroup$ And the solar shade could be built out of materials thinner than paper since it is in space and doesn't have to handle a corrosive atmosphere containing oxygen. Unlike planetary based options. Though I think reflective hydrogen balloons with a facility constantly pumping them out would be visually spectacular $\endgroup$
    – Pliny
    Commented Jan 29, 2021 at 18:37
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Since you mention that you also need to heat the planet, why not storing the heat you want to take rid from for later usage?

You could use something akin to sodium acetate heating pads

Sodium acetate is also used in heating pads, hand warmers, and hot ice. Sodium acetate trihydrate crystals melt at 136.4 °F/58 °C (to 137.12 °F/58.4 °C), dissolving in their water of crystallization. When they are heated past the melting point and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By pressing on a metal disc within the heating pad, a nucleation center is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The bond-forming process of crystallization is exothermic. The latent heat of fusion is about 264–289 kJ/kg. Unlike some types of heat packs, such as those dependent upon irreversible chemical reactions, a sodium acetate heat pack can be easily reused by immersing the pack in boiling water for a few minutes, until the crystals are completely dissolved, and allowing the pack to slowly cool to room temperature.

You would need some heat pumps to transfer the energy at some higher temperature, and you could reuse that heat later.

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Plant some trees in an dome that lets in greenhouse gases, and has an controlled atmosphere. Keep building more domes, and planting more trees within these domes, until the temperature is just right. Once that benchmark is reached, keep adding CO2 sources until the planetary temperature stabilizes.

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