QUESTION:
Being that Mars is composed of mostly red and orange materials, does that
imply that it is largely ferrous? If so, I would guess that there are many
local magnetic fields that could cause numerous problems with computer and
electronic equipment.  I have had stream current velocity meters go haywire
in Colorado streams because we were too close to fields of magnetite.  Once
away from these fields, the equipment functioned perfectly. Could this be
happening on Mars and be the cause of some equipment problems?

ANSWER from Geoff Briggs on August 12, 1997:
This is a very interesting suggestion and one that I will need to pass on to
others who know more about the history of iron on Mars.  I have not been
following the details of the Pathfinder radio reception problems to which
you refer so I can't comment on that -- other than to note that the Viking
landers missions did not seem to experience an interference problem.

Most of what we know about Martian iron mineralogy comes from telescopic
spectroscopy, from the magnet experiment on the 2 Viking landers, and
inferences from the Viking lander elemental analyses by x-ray fluorescence
technique.

There is a chapter entitled "Surface Chemistry and Mineralogy" in the U.
Arizona conference proceedings book "Mars" (Kieffer et al editors, 1992) by
Amos Banin, Ben Clark and Heinrick Wanke that discusses the whole subject
including iron minerals.

Selective quotes:
* Iron is the second most abundant (element) after silicon
* Reflectance spectra of the bright regions of Mars, believed to contain the
  more weathered components of the soil, show an intense though relatively
  featureless absorption edge from 0.75 microns to the near ultraviolet
* The major conclusion from the abundance of spectral analogs is that
  unambiguous identification of the iron mineral(s) in Mars soil, on the
  basis of spectral evidence only, is not possible at present.  The spectral
  evidence does imply, however, that iron in the weathered component of
  Mars soil is mostly present in the oxidized form (Fe3+) either in poorly
  crystalllized clusters of iron oxides or oxyhydroxides, or as crystaline
  minerals but in extremely small particle-size range ...

As you know, the martian soil was found by the Viking biology experiments
(which turned out to be chemistry experiments) to be highly oxidizing so I
have always supposed that all the iron would be completely oxidized to the
ferric form.

But I am a real non-expert on these matters so I will pass on your question
to others who will have more informed comments.

Geoffrey Briggs

ANSWER from Guy Beutelschies on July 25, 1997:
The amount of dust in the atmosphere is too small to affect communications.
If all of the dust in the atmosphere during a dust storm were condensed to
the surface it would only be a micron or two in thickness.  One way to think
of it is like haze (or smog) in terms of effect.

Guy Beutelschies        Mars Pathfinder Flight Engineer