CARNEGIE INSTITUTION OF WASHINGTON

Geophysical Laboratory

2801 UPTON STREET. WASHINGTON 8, D.C.

March 8, 1961

OFFICE OF THE DIRECTOR

Dr. Norman Horowitz
California Institute of Technology
Pasadena, California

Dear Dr. Horowitz:

l especially appreciated the comments in your January letter concerning
the version of my talk in New York. I have since revised the material and it
will appear in the April issue of the Proceedings of the National Academy of
Sciences. I followed up your comment concerning the work on growth of organisms
in a simulated Martian environment reported by Strughold and the group at
Brooks Air Force Base, ultimately obtaining a piece of literature entitled
“Microbiologic studies on ecologic considerations of the Martian environment”
by Irving Davis and John D. Fulton.

On reading this material it became clear that the experiments reported by
the Brooks group do not actually simulate a Martian atmosphere. The heart of
the matter is in the experimental procedures, Soil and organisms are dried and
mixed, water is then added to the soil in an amount to bring the moisture content
up to 3 or 4%. The mixture is placed in a closed Martian jar which is then flushed
with nitrogen to remove oxygen. This procedure leaves 3 to 4% water in the soil.
Once the flushing procedure is terminated, the relative humidity within the closed
space must rise to a value near 100% in contrast to the 1% or less present on Mars.
Another way of stating the matter is that a 3 or 4% free water content of soil is
incompatible with 1% relative humidity under equilibrium conditions.

‘cd ' VO STR Y

Having reached this conclusion I spoke with Captain Davis on the phone con-
cerning his experiments and he admitted to me that my view in this matter was
correct. I encouraged him to repeat his experiments, suggesting that it would
be possible to buffer the moisture content in an environment using an arrangement
analogous to that employed in a Warburg apparatus, with the buffer consisting of a
system such as sulphuric acid - water. He stated that he and hia group would
like to do such research when time permitted, but my guess is that he won't be
able to do the work immediately and it may be necessary for others to perform
the studies if these very important experiments are to be made soon.

Sincerely yours,

is roxED BY
ORTCINAL 5
puLLIP H- ABELSON
ce; Dr. Sagan Philip H. Abelson

Dr. Lederberg /