QUESTION:
Isn't it dangerous to bring Martian soil to earth?  Who knows what 
viruses it could have?

ANSWER from Dr. Robert Anderson and Marc Siegel on December 11, 1996:
The present missions have no plans to return Martian soil to Earth.
Such a mission is called "sample return" and NASA's current plans
call for a "sample return" mission to launch in 2005.  There is a
possibility that NASA will receive additional funding for this mission;
in that case it might be moved up to a 2003 launch.

No one knows now if a Martian soil sample brought to Earth would
contain viruses.  It is known that the surface of Mars appears very 
sterile due to the high amount of UV at the surface.  But life may
exists below the surface.  If a sample was brought back to Earth, it 
is almost certain that the sample would be isolated and not come in 
contact with the Earth's atmosphere.

ANSWER from Mark Adler on July 10, 1997:
We do have plans to bring back rocks, etc. from Mars.  We will be sending a
more capable rover in 2001 that go many miles for several months and collect
rocks, and another like it in 2003.  Then in 2005 we will send a rocket to
one of those sites to pick up the can of rocks from the rover (not the whole
rover!) and return the rocks as well as some dirt and Mars atmosphere to
Earth.  Two more sample return missions will follow that one in 2009 and
2013.

ANSWER from Jack Farmer on October 4, 1997:
If life were discovered on Mars or Europa, then there would be a potential
threat to the Earth's biosphere if samples were returned. Not surprisingly,
the concept of planetary protection is presently an important activity
within NASA, with a lot of advanced planning going on relative to future
samples returns. We are even worried about planetary protection issues in
connection with the cometary rendevous planned for early next century which
will bring samples back to Earth. If we do return samples from these places,
it will only be with extreme caution.

The National Academy of Sciences recently studied questions of forward and
back contamination, publishing their recommendations last year in an Academy
Report earlier this year. They recommended sample containment as a preferred
means for avoiding back-contamination, followed by quarantine. This is
preferred over sample sterilization (by heating or chemical cleaning)
because sterilization really has a big impact on the quality of science that
can be done. Implemetation of a planetary protection policy will be
complicated and will take a long time to accomplish. It will also need to
involve the global community. This is why NASA is investing a lot of effort
now in Public education and policy development of this critical issue.

(References: "Mars Sample Return: Issues and Recommendations" Space Studies
Board and National Research Council, National Academy Press 1997;
"Biological Contamination of Mars: Issues and Recommendations" Space Studies
Board and National Research Council, 1992)

Jack Farmer

ANSWER from Andrew Petro on October 20, 1997:
The sample return mission is still a few years off and I am not working on
that mission so I can't give you a very specific answer.  Someone at JPL
might know more about it.  But I'm sure that measures will be taken to
prevent any contamination of Earth whether they work with the CDC or not. 
Also it is important to make sure that the samples are not contaminated by
Earth organisms - so that there are no erroneous results when they are
analyzed.