STANFORD UNIVERSITY MEDICAL CENTER
Stanford, California 91305

September 17, 1971

Dr. John W. Findlay

Space Science Board
National Academy of Sciences
National Research Council
2101 Constitution Avenue
Washington, D.C. 20418

Dear John:

Elliott Levinthal has shared with me your letter of September 13th
with respect to proposed revisions in quarantine policy.

I am in accord with these proposals with the following explicit and
important exceptions:

1. I simply cannot agree that our present knowledge of Mars
justifies a further reduction in Pg. My own view of the
state of uncertainty concerning the possibility, for
example, of subsurface "permafrost" would lead me to assign
Pg = 10-4 as the model expectation in the light of present
knowledge, Roughly speaking I would assign P = 10°¢ for the
current estimate of the existence of extensive permafrost and
another 10-2 for the possibility’ that an organism deposited
on the surface will have an opportunity to reach that layer.

It may be sufficient to-say that if P, is drastically reduced the
same reasoning would make the design of current biology experiments on
Viking an absurdity, and this in turn would remove much of the scientific
interest that attaches to the exploration of Mars.

I believe that the present policies, predicated on Pp = 10°4 are a
reasonable accommodation of the diverse arguments that have been presented
in this sphere.

2. and 3. (Venus and Mercury). The revisions are in accord with my
own past doctrine that Py (surface) for both of these planets
approaches zero.

4. Outer Planets. STRENUOUS OBJECTION! I see great mischief in the
merry-go-round of the Jupiter values chasing the Mars ones and
vice versa. In the present state of our knowledge the a priori
probability of viable habitats in Jupiter probably exceeds that
for Mars. We know nothing of the altitudinal gradients of
temperature and molecular composition of the Jupiter atmosphere
and surface and quite plausible models have been presented that
John

JL/rr

W.

Findlay - 2- 9/17/71

would offer very attractive habitats at certain strata.
Whatever merit there may have been in comparing Jupiter
with Mars in the past is degraded by the progressive
decline of restraints for Mars. I would advocate a Jupiter
policy based on Pg, = 10-3 until further information on the
structure of the planet allows a more refined revision in
either direction.

I cannot object to including bus deflection within the

system analysis of contamination probabilities. ‘However,

the reason for the hitherto unwritten policy was undoubtedly
the difficulty of making credible estimates of the reliability
parameters. If the engineering numbers can now be tested then
certainly they should be explicitly included in the system
definition.

Orbital Lifetime - Mars. Hurrah!

Apollo - Inventory of Contamination. Yes, I think we can
relax on a detailed inventory of biological contaminants,
since the existing burden by now is already so high: f

would think there would still be some prudence in keeping
track of the physical and chemical composition of materials
that are deposited on the moon and then may later be recovered
and serious questions then brought up about artifacts.

Sincerely yours,

/s/

Joshua Lederberg
Professor of: Genetics