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Can Mars be magneticly shielded by Phobos placed in L1 point of Mars (between Mars and Sun)? Magnetic shield will aid in Martian atmosphere regrow.

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  • $\begingroup$ There is a list of many magnetic shielding of Mars questions here. The time scales are millions or billions of years so the benefit in the short term is minimal. It also requires a source for he magnetic field, does Phobos have a strong field? Also an orbit at or near L1 will suffer some instabilities, it may require a propulsion system to stay there long term. $\endgroup$ – uhoh Aug 11 '19 at 0:21
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Moving Phobos around takes an enormous amount of energy and as it does not have a magnetic field moving it to L1 wouldn't help anyway. Also, Phobos appears to be a rubble pile, so moving it is extremely difficult, it barely sticks together as it is and contains a significant amount of empty space. From Wikipedia: "The porosity of Phobos was calculated to be 30% ± 5%, or a quarter to a third being empty." Any force you apply to Phobos is likely to either simply compact it or break it up.

It might be better to invest that energy directly in building a magnetic field. This Japanese plan to build an artificial magnetic field for Earth makes more sense on Mars as it is much smaller, has no large seas and is geologically stable:

http://www.nifs.ac.jp/report/NIFS-886.pdf

Atmospheric erosion is an issue on geological timescales only; as such it is not relevant to terraforming or colonization. So there is no particular need to do any mega-projects to add magnetic shielding. Leave that for the technological capabilities of our descendants 100,000 years in the future.

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Phobos is very small, 27km on its longest axis, so it wouldn’t do much of anything to affect Mars no matter where it is.

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    $\begingroup$ you might want to add that a magnetic field is required and address if Phobos has one or not, and if it's strong enough. There is a list of many magnetic shielding of Mars questions here, further information might be available in some of those posts. $\endgroup$ – uhoh Aug 11 '19 at 0:24
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To create a field like Earth’s, you need to invest about $10^{20} J$ into creating the field (see this SE Physics item). You might be able to save a couple factors of two, but that still leaves you needing something comparable to a year’s entire energy output of the United States.

Interestingly, The mass of Phobos is about $10^{16} kg$, so the energy to lift it to L1 is somewhat comparable to the magnetic energy needed. So there’s a possibility to go the other way around: If Phobos was already at L1, could we drop it into a low orbit to get the energy needed to create a shielding field?

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    $\begingroup$ I think the idea of going to L1 is that you can shield Mars' atmosphere from much of the solar wind with a much smaller field at that point, than the field would have to be at the planet. I don't know how much smaller though. $\endgroup$ – uhoh Aug 12 '19 at 12:00

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