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A quick follow-up to How would it be possible to kick start Mars's magnetic field?

For example, the Venerean atmosphere is contained by merely an induced magnetic field.

  • How powerful would magnetic field need to be to contain sea-level Earth equivalent atmospheric pressure and composition as it exists today at Martian standard datum?
  • If future terraforming initiatives get some greenhouse effect going on Mars, would the magnetic field need to be gradually strengthened / reinforced as the Martian atmosphere also gradually thickened? Would the atmospheric escape rate to outer space increase as it thickens, or would interaction between the ionosphere and the solar wind sufficiently strengthen induced magnetic field on its own?
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    $\begingroup$ Magnetic fields do not hold atmosphere. Rather, a lack of a magnetic field means the solar wind is much more effective at stripping it away. $\endgroup$ – Loren Pechtel Sep 9 '14 at 3:50
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Earth's atmosphere is also slowly "leaking" into space, but very slowly. This is because there are multiple processes involved in escaping atmospheres. One of those processes is Jeans escape, where due to Maxwell speed distribution and long enough mean free path molecules are able reach escape velocity and escape the atmosphere before "bumping" into another molecule.

The dominant process for an escaping atmosphere differ from planet to planet. For example Venus has a very weak magnetic field and orbits closer to the sun, but has an atmosphere two orders of magnitude denser than that of Earth.

So giving Mars a strong(er) magnetic field and a "new" atmosphere does not mean its will keep it. It probably will lower the rate at which its atmosphere is escaping, however it will not stop it. I am not an expert on this, but I suspect that Mars is just too light to maintain a thick atmosphere, since more mass would increase its escape velocity.

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    $\begingroup$ Agreed it's probably impossible to stop atmosphere escaping. The rate of escape may be reduced though ... one means of reduction being a stronger magnetic field. I can't help going on a tangent here; wondering whether, on any given day, Mars' proximity to the asteroid belt means it accumulates more space dust than Earth does $\endgroup$ – Everyone Sep 8 '14 at 15:27

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