Here's my idea, tell me if it's feasible or what's wrong with it.

To make Mars hold an atmosphere indefinitely, it needs a magnetosphere to protect it from solar winds. If someone were to hollow it out and put all the ejected material on the surface until you had a hollow sphere the size of earth or bigger, you could turn the whole thing into a giant fusion reactor/Dyson shell which would have a magnetosphere.

I was thinking that by turning the inside surface into the containment system for a fusion reaction, you could slowly scale it up until you reach the point where the containment field plus the fusion itself would create enough of an EM field to ward off the solar wind.

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    $\begingroup$ How does making mars hallow create a fusion reactor? $\endgroup$ Aug 11, 2017 at 20:02
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    $\begingroup$ I guess if we are able to hollow out Mars, building a fusion reactor should be trivial. $\endgroup$
    – Alexander
    Aug 11, 2017 at 20:11
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    $\begingroup$ Welcome to Worldbuilding! By the looks of your question, you want to know if something is possible (terraforming Mars), given we can hollow it out. As such, you might want to edit the question to include the reality-check tag as well as possibly adding more details about how this would cause the magnetosphere (or how you could go about creating a magnetosphere from this) $\endgroup$ Aug 11, 2017 at 20:18
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    $\begingroup$ This entire "need a magnetosphere to keep the air in" is a red herring. Yes, without a magnetosphere some air will need to be added every million years or so, but then the entire frakking history since the most ancient clay tablets to the latest iPhone is less than five thousand years. Phenomena which need geological timespans are of no interest on the scale of human civilizations. $\endgroup$
    – AlexP
    Aug 11, 2017 at 22:17
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    $\begingroup$ NASA had something posted about placing a big magnet between the planet and sun to protect a Mars atmosphere from solar wind. $\endgroup$
    – rclev
    Aug 12, 2017 at 1:16

1 Answer 1


Hollowing out Mars would be a monumental task that would probably take millions of years using plausible mid future technology. While it could potentially be done, it would also be rather pointless.

Creating an artificial magnetosphere around Mars really only needs a superconducting loop placed at the L1 point and energized by a small fission react or even solar panels. Other means of terraforming mars creating a magnetosphere are also possible, depending on the amount of effort and resources you are willing to put into it. Even injecting antimatter into the core to melt it seems far simpler and less energy intensive than attempting to hollow out an entire planet.

As an aside, building gigantic "bubble worlds" seems feasible as a mega engineering project, but you would start by gathering material from asteroids to make the bubble. Multiple bubbles could be assembled together, or larger and large bubbles could be "blown" as experience in the technique is refined. The largest feasible bubble would actually dwarf what you are suggesting, an air filled bubble 400,000km across


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