Cha oo dy. ' fie

THE UNIVERSITY OF CHICAGO

CHICAGO 37+ ILLINOIS

THE ENRICO FERMI INSTITUTE
FOR NUCLEAR STUDIES

January 30, 1961

Dr. Joshua Lederberg
Stanford University Medical Center
Palo Alto, California

Dear Dr. Lederberg:

Thank you very much for bringing the error in my
manuscript to my attention. I had read your paper rather
carefully last August, immediately after its publication,
and thought I could trust my memory. However, it seems
that I wrongly attributed to you statements by other authors.
I am therefore offering to revise the first sentence of my
paper to read as follows:

"Several authors have discussed the possibility
that the Moon might serve as a repository for microorganisms
from outside the solar system, or “astroplankton" (1la,b,¢c,d)".

The references in question are:

la C. Sagan, Proc. Nat. Acad. Sci. U. S. 46,
396 (1960).

1b C. R. Phillips and R. K. Hoffman, Science
122, 991 (1960).

le J. B. S. Haldane, "The origin of life",
in New Biology (Penguin, London, 1954) yol. 16.

1a J. Lederberg, Science 132, 393 (1960).

The term "astroplankton" is used in your paper on
p- 397. Although Haldane does not give a complete definition
of this term, it is clear from the context of his discussion
(especially pp. 25 and 12) that he meant spores from inter-
stellar space. It would seem to me that while it was wrong
for me to say that you have "emphasized the importance...",
it is still true that you have "...discussed the possibility..".
I hope the present wording meets with your approval.

I also propose to change the penultimate paragraph
of my paper (pp. 6-7) to read as follows:

",..a factor of 3.3 x 10°, Hence a search for extra-terrestrial
biota has overwhelming odds against it, but, as pointed out by
Turkevich (9) the Moon may well yield samples of now-extinct

 
Dr. Lederberg January 30, 1961
eo

terrestrial microorganisms. At the observed frequencies

of meteorite infall (10), crater-forming_impacts of the
required magnitude may be expected at 10° - 10° year inter-
vals, and a fraction of the debris ejected from the Earth
may ultimately reach the Moon, after transit times ranging
from a few days to ~10! years. Indeed, the latest addition
to the Moon may have taken place in this century, after the
fall of the Tunguska meteorite (or comet) in 1908.

It would seem that these facts should warrant a
reconsideration of the goals of the lunar biology program.
The principal remaining objective would be a test of the
panspermia hypothesis, as provided by the presence or
absence of terrestrial microorganisms (1a). If a positive
result could be predicted with certainty on the basis of
present knowledge, the sterilization of lunar probes would
no longer seem as imperative as has sometimes been supposed
(1b), although a strong case could still be made for the
sterilization of planetary probes."

I agree that some delicate policy issues hinge on
a clear understanding of this problem. I am sure that you
will find most physical scientists anxious to cooperate
with you once they become convinced of the need for steri-
lization. To arrive at an informed opinion, they need to
know all pertinent facts. In my paper I have tried to
clarify one particular aspect of the problem.

I hope these changes meet your objections. As I
tried to indicate in my letter, I sent you the manuscript
in order to give you an opportunity to spot any errors and
misrepresentations before they appear in print. I dislike
polemics at least as much as you do, and therefore regularly
distribute preprints of my papers to about 150 workers in
the field. In the present case, I shall include an errata
sheet with the above changes.

Thank you again for your comments. With best
regards, I am

Cordially yours,

Aon, - - 9
Ct ce DS om
Edward Anders

EA:mb
ec: Dr. Carl Sagan

Miller Inst. for Basic Research

U. of Calif.

Berkeley 4, Calif. (with preprint)

 
A

Zé /

THE MOON AS A COLLECTOR oF
yr BIOLOGICAL MATERIAL

Bawaré(Anders )

Enrico Fermi Institute for Nuclear Studies
and
Department of Chemistry
University of Chicago

ABSTRACT

The Moon is not likely to contain detectable
amounts of microorganisms from outside the solar system,
Since this would require, on the average, the intact
ejection of twice the mass of the biosphere from rot
planets in the Galaxy. The ratio of terrestrial to extra-

solar-system biota on the Moon should be > 8.x 1072, and =
the addition of terrestrial biota by meteorite impacts on a
the Earth is likely to take place at intervals of 10° - 10° Oo
years. ™
=O
ON
~~
Lederberg (1) has recently emphasized the importance (v\

of the Moon as a possible repository of microorganisms from
outside the solar System. It is the purpose of this note

to discuss some quantitative aspects of this idea.

The first question to be asked is, what amount, W,
of microorganisms needs to be ejected from an average planet
in the Galaxy to give the minimum detectable density of 1
microorganism per square meter of lunar surface (2), or

10""*g/m°. Assuming a perfectly uniform distribution of this