QUESTION:
My question is about the landers on the planet's surface now and from the
past. The Viking Landers, which have been on the surface of Mars for quite
some time now, have been exposed to the elements of the planet, wind, dust,
etc. Is there any idea of what the elements on Mars is doing to these
landers (or the Pathfinder and rover in the future)? If there comes a day
when we could land on the surface of Mars, would there be a way to
dissasemble these and bring them back to study what the elements have done
to the material on these landers? The elements on Mars may have a different
impact on man-made equipment as compared to rocks.

ANSWER from Mark Adler on September 2, 1997:
We don't really know what's happened to the Viking landers since we stopped
communicating with them.  The only way to find out, as you suggest, is to go
visit them and maybe even bring some pieces back.  That's exactly what was
done on the Moon when Apollo 12 landed near the robotic Surveyor 3 lander
and retrieved the camera and soil scoop for examination on Earth.

In 2001 and 2003, we will sending sample collection rovers that will have a
small box on them to hold the collected rocks.  One of those boxes will be
returned to Earth in 2008 by a 2004 sample return mission.  We may put
patches of different materials on the outside of the boxes to test the
effects of exposure to the Martian environment over years.  This would be
like LDEF (the long duration exposure facility) orbited by the shuttle and
retrieved years later to determine the effects of space exposure on
materials.  But much smaller.

Eventual human missions to Mars may happen to land close enough to an old
robotic lander to bring pieces back, a la Apollo.  However the landing site
selection for humans will certainly not be dictated by that, and they may
well end up too far away for that.