Could Mars's magnetic field be restarted by its own moon? I've done some research (and I am definitely no scientist) but I am looking for answers. I know that Mars has two moons, one of which is on a orbit that could end in it hitting the red planet. Could this lead to the restarting of Mars's magnetic field, blocking deadly solar radiation, allowing liquid water to form and stay, and creating weather--and ultimately, a habitable planet apart from Earth on which we could start our first ever colony?
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$\begingroup$ Mars has a partially molten core, just as does the Earth. Mars does not have a magnetic field because the heat transfer rate across the core-mantle boundary is too low to sustain a magnetic field. The problem is that Mars's surface is geologically inactive, keeping heat bottled up in the core. Start (or restart) plate tectonics on Mars and voila! you'll eventually have a magnetic field. This will take lots of water and lots of time. It might not last long, because then Mars's core will soon freeze solid ("soon" meaning soon in geological terms). $\endgroup$– David HammenOct 21, 2016 at 9:35
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$\begingroup$ @DavidHammen, I'm not doubting what you're saying- it seems reasonable, but do you have any further reading or simulations that I can look at? $\endgroup$– Mohammad AtharOct 21, 2016 at 15:45
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$\begingroup$ DavidHammen, I too would like to know more about what you say. The work of the late Mario Acuna on the Mars Global Surveyor provided rather convincing evidence that Mars' global magnetic field dramatically decreased more than three billion years ago. My understanding is that this was because Mars' core cooled much faster than Earth's so that it began to vitrify. Since Mars' mass is about a tenth of Earth's, its heat capacity is also about a tenth. Having a smaller diameter, it has a larger surface to volume ratio. If this isn't correct (or complete), I'd like to learn more. $\endgroup$– Vince 49Oct 21, 2016 at 16:38
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Short answer: No
Simply hitting a planet with a big rock does not create a magnetic field. Earth has a magnetic field because it has a molten core which spins. Mars may or may not have a partially molten core, but even if it's partially molten it's not molten enough.
In order to have a magnetic field on mars you'd have to melt the entire core somehow, and to do that from the outside you'd have to turn the whole planet molten again. That's a lot of small rocks or a few big ones. The trouble with that method is you'd then have to wait the thousands or million years for the outside to solidify enough to be habitable again. We are barely able to move a single small space rock at the moment, and that's only theoretical as it hasn't been tested in practice.
So, is it theoretically possible to give Mars a molten enough core to have a magnetic field? Yes, if you have massive resources, incredible technology, and are willing to wait thousands of generations.
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$\begingroup$ Mars's core is not frozen solid. Mars has a molten outer core, just as does the Earth. Mars has no magnetic field because Mars does not have plate tectonics. Mars's surface is instead in a stagnant lid regime, which makes heat transfer across the core/mantle boundary too low to sustain a dynamo. $\endgroup$ Oct 21, 2016 at 9:12
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$\begingroup$ That's not confirmed @DavidHammen, it's a theory which is not agreed. You have a point in that even if it is partially molten it's not molten enough, I will edit accordingly. $\endgroup$– GdDOct 21, 2016 at 14:02
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$\begingroup$ Which part is not well agreed? That Mars' core is at least partially molten (just like Earth) has been well known since 2003: science.sciencemag.org/content/300/5617/299 . That a sufficiently high heat transfer rate across the core mantle boundary is essential for the creation of a geodynamo on a terrestrial planet has been well known even longer. That plate tectonics is one of the ways of getting that high heat transfer rate is also well known. (Another is rampant vulcanism.) That a stagnant lid regime is a way to keep the heat bottled is also well known. $\endgroup$ Oct 21, 2016 at 15:53
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$\begingroup$ For example, see annualreviews.org/doi/abs/10.1146/annurev-fluid-122109-160727 . $\endgroup$ Oct 21, 2016 at 15:54