QUESTION:
If Terraforming was ever undertaken, what could be done to shield Mars
from the bombardment of cosmic radiation due to the lack of atmosphere on
Mars? Could an electro-magnetic field be generated artificially creating safe 
zones?

ANSWER from Bob Haberle on February 14, 1997:
Actually, Mars does have an atmosphere! Even though it is thin by comparison
to Earth (mean surface pressures on Mars are about 7 mb compared to 1013 mb
here on Earth), it provides about 15-20 gm/cm**2 of shielding for surface
operations. There are three sources of radiation: the solar wind (protons
streaming away from the sun); cosmic rays (very high energy particles), and
solar flares. You can expect about 10 REM per year from the solar wind,
and 30 REM per year from cosmic rays. Solar flares are difficult to predict,
but a conservative estimate might be 60 REM per year. Thus, the total exposure
is about 100 REM per year from these three sources. Since OSHA standards
allow for about 300 REMs for an entire career, something must be done to 
reduce the radiation exposure on Mars. 

Bob Haberle

ANSWER from Mark Adler on April 30, 1997:
Assuming that terraforming includes an Earth-thick atmosphere, then
you have taken care of some of the radiation from space.  However as
you point out you lack the shielding effect of Earth's magnetic field.
Not much can be done about that with any forseeable technology.

In general, whether you terraform Mars or not, you will likely use
Martian dirt to shield your abodes, and you would tend to not spend a
lot of time outside unshielded.

mark

ANSWER from Peter Thomas on June 1, 1997:
When people finally go to Mars, there are different parts of the problem: 1)
going to Mars, and 2) time spent on Mars.  Solar flares are the main
concern.  Spacecraft generally cannot carry heavy shielding, so the transit
to Mars has to use imagination, such as crew quarters as much inside other
equipment and fuel tanks, or areas to be in during solar flare events.  On
the surface, Martian soil could be used for living quarter protection. 
Obviosuly, this all depends upon ability to use other satellites to tell
when solar flares are occuring, and the willingness to have background
exposures greater than those of airline crews.  The Mars atmosphere provides
some protection, but not as much as ours, and our magentic field, which is
absent on Mars.

Peter Thomas