Cooling a planet

[madd0ct0r]

new terraforming trick I've just come across:

build rings (like saturns) around a planet to help cool it.

they cast a shadow, basically.

http://www.guardian.co.uk/science/punct ... 1/may/02/1

not exactly hard science, hence why posting here.

[sirocco]

new terraforming trick I've just come across:

build rings (like saturns) around a planet to help cool it.

they cast a shadow, basically.

http://www.guardian.co.uk/science/punct ... 1/may/02/1

not exactly hard science, hence why posting here.

Well that may be useful for Venus-like planets. But first you'd need a good guestimate of mass and composition of the rings.

[Simon_Jester]

Build big hollow frames with aluminum foil wrapped around them- it's much cheaper than bringing in enough rock for Saturn-style rings, and more efficient. You're basically looking for something like solar sail fabric- and yes, you do need to worry about the propulsive effects, at least slightly.

[someone_else]

Bah, just nuke the moon. Repeatedly.

For a slightly more rational project, you just need a sail (+ its frame) big enough to do a total eclipse (the size depends from the distance from the sun it must mantain), and have it say partially trasparent, so that only an arbitrary quantity of sunlight reaches the planet. "Planetary sunglesses", much more classy.

I wonder what the hell would ancients think about the "strips in the sky", and the "moving shades" under them.

[Sarevok]

Would introducing a global ocean help cool the planet via convection currents ?

[Serafina]

Alternative:
Cover most of the surface in a white color. This will reflect a large amount of solar radiation back into space.
This happened to Earth at least once, during an extreme ice-age. Most of the planet was covered in ice, because more ice cooled it down, which lead to more ice and more cooling, and so on (we got out of it by volcanic activity and more greenhouse gases).
On that note, keep the greenhouse gases in low concentration.

This doesn't require any space construction. And of course, you could do it in addition to space construction.

[madd0ct0r]

Well to terraform a planet, we'd have to actually get there, so my assumption is always to start in space.

And this caught my eye becuase it doesn't need huge amounts of dedicate construction. As someone-else suggests, just dismantle a moon.

I would actually expect the ring creation to be a useful side effect from strip mining asteroids, moons or their ilk. Of course, there doesn't tend to be many asteroids near the center of a system, which is where the hot planets are.

Think of it as an interstellar equivalent as using mining waste for road construction.

[Darth Tedious]

Ringworld-style Shadow Squares! Why cool just one planet, when you can make regular eclipses for every body in the whole star system?

Alternative:
Cover most of the surface in a white color. This will reflect a large amount of solar radiation back into space.
This happened to Earth at least once, during an extreme ice-age. Most of the planet was covered in ice, because more ice cooled it down, which lead to more ice and more cooling, and so on (we got out of it by volcanic activity and more greenhouse gases).
On that note, keep the greenhouse gases in low concentration.

This doesn't require any space construction. And of course, you could do it in addition to space construction.

Another way of lightening the surface of an Earth-like planet would be to get rid of all those really dark trees that capture so much heat, but that would lead to other terraforming issues...

And interesting side thought is that a desert planet (like Dune or Tattooine) would need to be closer to the sun than Earth is to maintan a habitable temperature (maybe less so in the case of Tattooine though, what with having two suns).

[madd0ct0r]

also had a thought this morning in the shower.

for those paranoids among you - it's a lot harder to destroy or manipulate a planetary ring compared to a solar shield.

[Purple]

But would destroying a moon and otherwise introducing a large change into the mass present in the orbit of a planet wreak havoc on the tide pattens and generally mess up the environment?

[someone_else]

Dunno, rings are very ethereal.
Saturn's ones seem to be 3E19 kg. Earth's moon is 7E22 kg, so Saturn's rings are somehwere around 1/1000 th of the moon mass.

The ones for Earth will likely be much lighter.

[Lord Relvenous]

Isn't the easiest way to cool a planet to throw particulates into the air with impactors? Essentially a nuclear winter without the nukes. Or am I missing something?

[Sithking Zero]

I guess a nuclear winter type situation could work, but the problem with that is the whole, "The point of Terraforming is to make the place livable, so I wouldn't do that. I mean, I guess with kinetic impacts from orbit, it could be without the radioactivity, but plants and animals don't survive in a nuclear winter. Plus, what's the soil composed of? That could have an effect on how long the winter would last, or what it would be like.

[Lord Relvenous]

Well I suppose I overstated my point. Nuclear winter wouldn't be the desirable level, but even things like large volcanic eruptions have introduced enough particulates into the atmosphere to effect temperature. Krakatoa dropped the global climate by as much as 1.2 degrees Celsius. A space faring civilization could pretty easily introduce enough matter into the upper atmosphere to drop the temperature by enough, I'd think. While it wouldn't be permanent, they could reintroduce the particulates on a regular basis.

Just a thought. It doesn't take anything as grand as formulating a stable ring system for a planet, at least. Just some impactors in a remote location.

[Purple]

On the other hand, it would be much harder to clean up than just moving a bunch of asteroids out of orbit again. After all you don't want indefinite cooling. Also, as far as I understand making a ring around a planet would also give you fine control over the cooling process. All you would have to do is modify the composition of said cloud slightly. I don't think you can do that if you fill the atmosphere with ash.

[Lord Relvenous]

On the other hand, it would be much harder to clean up than just moving a bunch of asteroids out of orbit again. After all you don't want indefinite cooling. Also, as far as I understand making a ring around a planet would also give you fine control over the cooling process. All you would have to do is modify the composition of said cloud slightly. I don't think you can do that if you fill the atmosphere with ash.

Seeing as how a planetary ring is made up of billions of particles, I think the cleanup would be harder than you think. Also, the cooling would reach an equilibrium. All the particulates do is reflect sunlight and keep it from reaching the surface. After the initial period of cooling, it wouldn't continue as a stable amount of sunlight would be reaching the surface.

[madd0ct0r]

cleaning up a planetry ring would be nigh impossible.

it would need much less ongoing maintenance then the particulates, which if the feeding stopped would disappear in a few years (depending on surface liquid, winds ect)

I'd prefer a long term stable solution personally, but the particulates would be ideal as a start point. Get the planetry tempreture down to just above what you want, and start building the ring. As temperature drops, slowly phase the particles out and pray you don't hit a tipping point.

[someone_else]

cleaning up a planetry ring would be nigh impossible.

I was thinking about gravity tugs. Technically those are the same kind of machinery you will want to use to shape the ring in its flat pattern without risking dangerous screwups (= filling lots of orbits with fucking huge quantity of high-speed debris after collisions, like Chinese did with their ABM test).
It will take a lot of time (as much as setting the rings up anyway), but in the end you destabilized all the thrown crap's orbits to reenter atmosphere.
Given that the average size of such crap is big fridge/average pickup, they won't survive reentry.
Otherwise you can shepherd them into a slightly thicker ring if you don't want to lose them.

Of course, this allows you to make a bigger ring to speed up the cooling, and then erode it as the planet approaches the temp you need (if all this happens in decades, you have all the time you need).

Just a thought. It doesn't take anything as grand as formulating a stable ring system for a planet, at least. Just some impactors in a remote location.

Yup. Even redirecting a dinosaur-killer asteroid is a joke in comparison of making a stable ring system from scratch. And the thing killed dinos with climate change mostly.

but plants and animals don't survive in a nuclear winter

tangential to your point, but still relevant: indigenous life is not likely to survive terraforming anyway. (terraforming by definition is enacted when the environment has to be drastically changed)

[Sky Captain]

A ring system would mess up all other space activities. Imagine launching a sattelite or launching anything when most orbits pass through the rings with resulting high chance of high speed collisions.

[StrikaAmaru]

In the realm of we-might-just-theoretically-achieve-with-this-century-tech, I'd go with an irregular ring of ice and dust, at and around the equatorial band. Push some icy asteroids in orbit with tugs, then blast them with solar mirrors, over a long, long time. Water vapor and whatever solid chunks were trapped in the ice would make a fine shade, yes? A near-planet one (below the Roché orbit/limit, if memory serves) would have the added benefit of slowly (10^5 years) sinking into the atmosphere, so if you use some water ones, you have extra benefits for a ground-up terraforming effort.

Increasing the albedo by covering the planet in something white (what exactly? Calcium carbonates? Titanium oxide? White cloth with a nanoweave base?) is tempting, but it's a solution (like all of them, actually) that requires centuries, and if the planet has even a semblance of atmosphere - and therefore, wind and weather - it will get damaged; if the planet has no atmosphere, why bother? I'm also discounting ice, because if we'd have a significant portion of the planet covered in ice, it probaly won't need cooling. I remember Earth has no winds +/- 5 degrees of the Equator, so there's a possible target for an albedo solution; I can't remeber why that happens, though... It definitely wouldn't work on Mars, for instance.

and now, something different, but still kinda the same. I was thinking something on this subject a few months ago... specifically, about how could the excess-heat problem be addressed on a Coruscant-type planet. This might actually be off-topic for this thread; from what I gather, madd0ct0r wanted a passive cooling system, to shield a planet from externally-generated heat radiation, and both ideas I had were about rapidly moving internally-generated heat outside the planet. I say cooling a planet-city is sufficiently on-topic, so I'm posting anyhow.

Both systems are, in essence, mind-bogglingly huge radiators, connected to an elliptical backbone, with their perihelion in the planet, and the aphelion either beyond geostationary orbit on the other side of the planet (the first, and largest one) or below geoSync, and tethered to one, or several concentric, orbital ring(s), which also means it's an active system, and the power better never shut down.

The second backbone, being inherently unstable, would need the core to stay aloft, as I don't expect an orbital ring to provide enough lift to support the whole thing. The first one should be stable on it's own, but still borrows the maglev internal structure from launch loops and orbital rings, because it's crucial to the purpose of the radiator; heat transfer from planetary surface to outer space is done by lifting hot packets to the radiators, letting the head bleed off into them, then dropping the cool transfer medium back on the planet. This transfer system is the reason why I didn't just build a space elevator for it. Heat transfer packets would consist of hot liquid, packed for transit, then once reaching aphelion, unpacked and left to contact/flow through the radiator; I'm counting on gravity here. Then it gets repackaged and break-descended into the gravity well. and I just now realized you'd need a twin-rail backbone, with packets travelling in opposite directions, each feeding the radiator in the opposite side.

Problems I can think up so far:
- how much heat does this move outside the planet, and can more than one be built?
- the system has its own heat output.
- radiator bodies are vulnerable to impacts (micro- and macro-meteorites) which could rupture radiator fins, or worse, damage the backbone. The vision of even one second-type radiator collapsing on the planet would be a good reason to never build a planetary city in the first place.

[StrikaAmaru]

A ring system would mess up all other space activities. Imagine launching a sattelite or launching anything when most orbits pass through the rings with resulting high chance of high speed collisions.

The problem this thread has is that there are too many different cases lumped together. I see two distinctions here:

If the planet is terraformed for human habitation, that's not a problem; there are no humans on it to launch anything. When it comes to an already inhabited planet, with a runaway greenhouse effect people are trying to mitigate, well, that's different.

Speaking strictly in the case of Earth, in the near-ish future (100-500 years): currently, most orbital activity happens in LEO, or in geostationary orbit. Anything outside that consists of several research sats in highly elliptical orbits (Chandra, for instance). I find it a reasonable assumption that any space development will happen in LEO (space stations and habitats) or geosynchronous (space elevators, not necessarily for human transportation - although I doubt their feasibility nowadays; pesky Van Allen belts)

A relatively "jagged" ring could be made outside of geosynchronous orbit; I described a hopefully plausible method in the post above, and I'd add that if they use icy asteroids, that's some wasted water, because solar wind will push small particles away relatively fast; depending on circumstances, that may in fact be an advantage. It also means that the mass of asteroids to get broken up would substantially increase, making the orbital sunglasses option more attractive for this particular scenario. And incidentally, the Kyoto Accord keeps looking better and better.

[Cykeisme]

Would I be wrong in saying that an artificial ring (or in fact any orbital objects intended to block a parent star's radiation) would make the most efficient use of their surface area by being in as low an orbit as possible? It would "cast a larger shadow" that way.

[Ahriman238]

Would I be wrong in saying that an artificial ring (or in fact any orbital objects intended to block a parent star's radiation) would make the most efficient use of their surface area by being in as low an orbit as possible? It would "cast a larger shadow" that way.

To a point within reason, yes. The closer to the planet the ring is, the more it's affected by the planet's gravity. Even if the ring doesn't start shedding bits right away, there must be a point where the added stress would outweigh the benefits of maximizing surface area.

Worse, where that point is will likely have to be decided on a case-bycase basis. Though I'm sure there are people here who could come up with a ballpark estimate.