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Supposing that we managed to speed up Venus's rotation to a 24 hour cycle in just under 40 years (how we managed to do that is irrelevant here), how much time would take for Venus to form a magnetic field?

Considering that the existence of a magnetic field is related (but not exclusive) to a planet's rotational period, what is the timescale we could be seeing? 100 years? 1000? A million?

Edit: I replaced 'magnetosphere' to 'magnetic field' as JBH recommended below.

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    $\begingroup$ /Considering that the existence of a magnetosphere is related to a planet's rotational period/ - that is news to me. Can you link a reference about that relationship? $\endgroup$
    – Willk
    Dec 11, 2022 at 22:04
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    $\begingroup$ Why would there be any relationship between the rotation period of a planet and the presence or absence of a magnetosphere? (For example, Mars has about the same rotation period as Earth; Earth has a magentosphere, Mars doesn't.) And why do you care about Venus having a magnetosphere? $\endgroup$
    – AlexP
    Dec 11, 2022 at 22:11
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    $\begingroup$ Why you want a magnetosphere is unimportant. How magnetospheres form is important. First, there's a difference between a planet's magnetic field and the magnetosphere, which is caused by the interraction of the solar wind with a planet's magnetic field. So what you're really asking is how to create a magnetic field. "Planetary magnetic fields are formed by the interaction between the convection of interior conducting material (molten rock and metal) and the planet's own rotation. Mercury's field is weak because... (*Continued*) $\endgroup$
    – JBH
    Dec 12, 2022 at 1:45
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    $\begingroup$ ... it rotates so slowly." (Source) So you are correct that rotational speed is involved, but it's not the only variable. If a planet is formed completely of rock, all the spinning in the universe won't create a magnetic field. There must also be metal. Good for you Q, Venus has an iron-nickel core. So, spin it up fast enough and you might get a magnetic field. Therefore, it's my opinion that this Q is reasonable. (*Continued*) $\endgroup$
    – JBH
    Dec 12, 2022 at 1:47
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    $\begingroup$ ... However, it would help a lot if you edit your question and replace "magnetosphere" with "magnetic field" to avoid the inevitable confusion. $\endgroup$
    – JBH
    Dec 12, 2022 at 1:48

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Probably never. See https://web.archive.org/web/20100714051425/http://www-spc.igpp.ucla.edu/personnel/russell/papers/venus_mag/

"It is important to note that, contrary to popular belief, dynamo theory does not credit the smallness of the magnetic moment to the slow rotation of Venus (a Venus day of ~ 243 Earth days is almost equal to the length of its year of ~ 224 days, and its sense of rotation is retrograde). It is also notable that Venus would not have maintained any remanent crustal magnetic fields from its proposed early period of dynamo activity because the temperatures in the crust are expected to be above the Curie point (below which such fields could persist in rocky materials)."

Earth's magnetic field is created not just by the spin of the planet, but by convection within the molten core. Venus may well have had an Earth-magnitude magnetic field for the first billion years of its life, but lost it once that convection ceased.

For the creation of artificial planetary magnetic fields, you might want to have a look at this: https://www.sciencedirect.com/science/article/abs/pii/S0094576521005099

It seems far easier to put a set of superconductors across the surface, or in orbit, than it does to restart core convection.

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  • $\begingroup$ I remember doing calculations like this at college for Mars. I think it would take a loop of superconductor carrying about 500A around the equator, assuming you wanted to stabilise an atmosphere, and taking into account we were further away from the sun so we could use half the field. Sounds plausible but the energy taken to power it up would be huge. And it all gets out if the wire breaks. $\endgroup$
    – Richard Kirk
    Dec 12, 2022 at 15:29

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