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Here, I asked if it's possible to terraform a hot planet. But now, if we have a volcanic active planet, can we use the same techniques to cool it down?

  1. Normally, the planet cool off slowly after its formation. Is there any way to speed up the process?
  2. Some planets like Venus have formed billions of years ago but are still very active, with lot of volcanic eruptions. is it possible to lower this activity to make the planet more hospitable?
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  • $\begingroup$ A lot of the reason for Venus' high temperature is the thick atmosphere and greenhouse effect, not the core. $\endgroup$ – Tim B Oct 21 '14 at 15:36
  • $\begingroup$ Lots of water. But try to avoid explosions. $\endgroup$ – Shokhet Oct 21 '14 at 15:41
  • $\begingroup$ Are you asking about a natural process, or an artificial one? $\endgroup$ – Shokhet Oct 21 '14 at 15:53
  • $\begingroup$ it could be both $\endgroup$ – Vincent Oct 21 '14 at 15:54
  • $\begingroup$ @ Tim B: the planet is also active with many volcanoes, no ? $\endgroup$ – Vincent Oct 21 '14 at 15:56
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Volcanic planets are actually in the process of cooling themselves down already (see bolded answer further down.) In addition, the heat is not from the volcanoes but rather the greenhouse effect. "Venus is hotter due to the greenhouse effect: Venus has an atmosphere about ninety times thicker than that of Earth, and made almost entirely of carbon dioxide, which is one of the gasses that causes the greenhouse effect on Earth." (Source). As such, most of the following keep that in mind.

DRAIN ATMOSPHERE Draining the atmosphere from the planet by ejecting it would be one way of dealing with it. Since a hot volcanic planet probably has a very thick atmosphere, this might actually help terraform it towards livable conditions. The opposite problem that Mars has. Pros: Can help terraform a planet towards our own tolerance. Cons: Difficult to achieve and astronomically expensive.

SPACE SHIELDS Steerable micrometers-thick refractive screens could divert a portion of the sun’s energy away from planet, thus cooling the atmosphere. The screens would orbit between the sun and the planet.
Pros: No pollution; can be turned on or off quickly.
Cons: Even using futuristic launching technology, the 20 million metric tons of mesh would cost $4 trillion to deploy

SPACE DUST Reflective particles in low orbit reflect sunlight and cool the planet.
Pros: Closer orbit and low manufacturing costs could make dust cheaper to deploy than space shields.
Cons: Costly to deploy and would require frequent replenishment as solar radiation drives dust down to planet.

PARTICLES IN THE STRATOSPHERE Sulfate or other reflective particles injected at the equator stay aloft in the stratosphere for one or two years, reflecting sunlight and cooling the planet.
Pros: Principle proven by volcanic eruptions; $130 billion price tag is relatively reasonable.
Cons: Increased acid rain, ozone layer damage.

REFLECTIVE BALLOONS Reflective balloons would bounce a portion of the sun’s energy away from planet before it had a chance to warm the surface or the lower atmosphere.
Pros: Cheaper to launch than space shields or space dust.
Cons: Would require millions of balloons that would eventually fall to planet as trash.

CLOUD COVER Ships spray salt-water droplets that make ocean clouds more long-lasting and reflective, cooling the planet.
Pros: Pollution free.
Cons: Would take some 5000 salt-water spraying ships, at \$2 million to \$5 million apiece, to counter a carbon dioxide doubling.

IRON DUST Iron particles spread over unproductive parts of the ocean cause photosynthetic plankton blooms. The plankton absorb carbon dioxide. When they die, they carry some carbon to the ocean bottom.
Pros: Some experiments indicated that thousands of metric tons of carbon were absorbed per metric ton of iron.
Cons: Unclear how much carbon is permanently trapped; plankton blooms can poison other sea life.

REFLECTIVE ROOFS Simply painting roofs and roads white could cool populated places by reflecting sunlight.
Pros: Paint is cheap.
Cons: A small effect because much of the sun’s energy is absorbed in the air before it reaches the ground; cooling is local and so could make the local weather worse.

SEQUESTRATION Carbon in the atmosphere or in smokestacks is converted to a form that can be stored underground.
Pros: Already being intensely investigated.
Cons: Could be expensive to deploy the technology and store the carbon; carbon reservoirs could leak.

REFORESTATION Trees pull carbon dioxide out of the air and use it to form wood.
Pros: Uncontroversial and already accepted under the Kyoto Protocol.
Cons: Most carbon uptake happens only in the early part of a forest’s growth; new forests could compete with agriculture for land and water.

Original Source for the previous ideas modified slightly by myself (added drain atmosphere).

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  • $\begingroup$ Information copies from the links as per SE preferred policy (thus the large amount of mostly direct copying) $\endgroup$ – Mourdos Oct 21 '14 at 16:18
  • $\begingroup$ If you already have life forms living on the planet or are safely able to store large amours of carbon under ground that a volcanic planet is already largely terraformed (probably between 0 and 70 degrees Celsius). $\endgroup$ – Thijser Oct 21 '14 at 20:34
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    $\begingroup$ "20 million metric tons of mesh would cost $4 trillion" - we could build a massive space net and cool down venus, for the same rough cost as the war in Iraq? $\endgroup$ – NPSF3000 Dec 6 '14 at 0:43
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I think there is a confusion here, for the most part volcanoes are a symptom of the heat of the planet, not the cause of it.

When a planet forms it's a super-heated ball of lava. Gradually that Lava cools and the heat escapes, radiating out into space and carried off with escaping gasses.

Over time an equilibrium forms when the incoming heat from the sun and from nuclear reactions within the planet's core matches the outgoing heat lost into space. The position of that equilibrium is what determines the conditions on the surface.

If the crust is thin and the surface volcanic then that means either less of the heat has escaped or more is being generated. In the case of Venus it's a combination of being closer to the sun and having a thick and heavily insulating atmosphere. So far as I know we don't have any real detailed information on what lies below the surface so we cannot speculate as to any further heat sources there may be.

Cooling the planet will reduce the number of volcanoes as it causes the crust to thicken. The problem is that we are talking a huge amount of energy that would need to be lost. There is no known technology that would do the job in less than centuries, probably you would need thousands of years.

First you would need to change the atmosphere, possibly by seeding it with specially engineered bacteria assuming you can even engineer them that will survive those conditions. You would need to scatter reflective particles in the upper atmosphere, and then you would still need to construct heat shields in space to reduce the incoming heat from the sun, and that's just to get you started!

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Eventually the gasses caused by the volcanic activity would condense and create an atmosphere. As the atmosphere thickens it would condense. Depending how close the planet is to its parent star the atmosphere would condense its gasses causing rain-ice building oceans, or creating thick dense atmospheres of carbon dioxide and nitrogen raining sulfuric acid. Pick your planets wisely.

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  • $\begingroup$ "Pick your planets wisely" - no kidding! :-) Welcome to Worldbuilding. I don't think this properly addresses the question, but it's a good start. Can you expand this? $\endgroup$ – HDE 226868 Oct 22 '14 at 1:10

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