ake STANFORD UNIVERSITY MEDICAL CENTER
R STANFORD, CALIFORNIA 94305 © (415) 321-1200

 

STANFORD UNIVERSITY SCHOOL OF MEDICINE
Department of Genetics March 15 ; 1972

Dr. Richard S. Young

Chief, Exobiology ;
National Aeronautics and Space Administration
Washington, D.C. 20546

Dear Dr. Young,

We have been given the difficult task of recommending a Viking
Biology experiment for removal from the payload. The differences
are not compelling from a scientific standpoint. We were told,
nevertheless, that one experiment had to be dropped, and that we were
to disregard engineering reliability considerations, which others had
judged to be given’no basis for choice.

Given these premises, we have concluded that the light-scattering
experiment be selected. Dr. Vishniac is, however, one of the most
valued scientists in exobiology and should be strongly encouraged
to retain a vital role in the Viking mission, particularly in association
with the gas exchange experiment. (In terrestrial biology we do not
make a close identification of a scientist with a particular instrumental
sensor.)

Our reasons, insofar as so tenuous a judgment can have a rational
basis are:

1) The difficulty of interpreting turbidity as necessarily a result of
microbial proliferation, rather than, for example micro-dispersion of
soil particles. _
2) The lack of any secondary utility if the result is negative. (If

there is no proliferation there should be nothing to measure, and we

will not have improved our knowledge of the physico-chemical habitat) gesnm

3) The a priori likelihood that organisms adapted to ultra-arid
environments will not have a dispersed growth habit in a liquid medium.

4) Technical problems that may be expected from dust contamination,
which may increase the noise signal level.

Except for (2) these are not categorical criticisms and much thought ©
has been given to answering them, but we conclude that this experiment
may be somewhat more vulnerable than its competitors on these grounds.
The secondary potential of the gas-exchange experiment is one reason
for preferring it. This is the alternative probe for responding to the
contingency that Martian organisms can survive very high water-activities.

Sincerely yours,

co fo ARA (et) DQ foe

Boe ae <

- Lad
LT. J. P. KENNEDY, JR. LABORATORIES FOR ‘CULAR MEDICINE, DEDICATED TO RESEAR IN MENTAL RETARDATION

MOLECULAR BIOLOGY HEREDIT Y NEUROBIOLOGY DEVELOPMENTAL MEDICINE

Joshua Lederberg

ra IV AOA

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