Subject: How powerful a magnetic field is necessary to prot

I have always questioned when people talk of terraforming the planet Mars.  If
it's lost its atmosphere before it seems a waste to import/create an atmosphere
for it only to loose it again.  Now that I have learned that the magnetic field
of a planet is what protects its atmosphere from solar and universal radiation
it seems like a real possibility.
related inquiries:
Could you create a sufficient magnetic field be generatable from the surface of
a planet maybe by magnetizing the crust of the planet?
Once you have a sufficient magnetic field to protect the atmosphere how much, if
any, gravity is necessary to reasonably hold it?  Would it be possible to
magnetize the moon and atmosphericly terraform it?  Would a magnetic field of
the Moon be problematic or reinforcing or neither to the Earth's magnetic field?

Re: How powerful a magnetic field is necessary to prot