October 15, 1963

Or. N. &. Gibbons

Division of Applied Blology
Nationa} Research Counc! 1!
Ottawa 2, Canada

Bear Or. Gibbons:

Thank you for your communication of September 26 relative to the action of the
IAMS soliciting appraisals of the problem of planetary contemination. You
are probably already well acquainted with my ow position on this subject

and | have not lacked for an opportunity to make It know to COSPAR and to
national agencies involved In spece research. There ere Just two points that
1 would like to stress In the general picture:

1) Astronomical determinations of the parameters of the Mars surfece ere
subject to a large uncertalaty, unknown In direction end quantity. We should |
be cautious about relying on assertions as to the best estimates of tempera-
ture, water concentration, and other parsaeters which are likely to suffer
considerable local variation. The only way ! have been able to assimilate all
of the considerations fs to establish sase number as representing the equiv-
alent damages of unwonted contamination and then to aultiply this cost by a
series of factors representing our best estimates of the probabliity of an
undesired result. For example, if one were to conclude that there wes a
residual likelihood of the order of .01 thet Mars had resources of water
readily avaliable to orgeniems, then this consideration would possibly lead
to # reduction of the ‘equivalent cost'' (expected value) by the same factor,
.O1, provided this was # necessary condition for the Habllity of damages by
contamination. The sane sort of factors must be considered In assessing the
ltkel thood of failure of sterilization, the Ifkellheod that an organism would
survive Impact, that given other factors It would be able to proliferate, etc.
Our course of action would then be besed on a prudent and to some extent cal«
culable balance between our assessment of the values at risk, on the one hand,
and the possibilities of prejudicing these values on the other.

2) It has usually been taken for granted that the disturbance of existing
life was the main ''value’ which wes at risk In planetary contamInation. while
| would certinly plece a very high priority on this consideration, It should
not obscure others. For example, even if Mars were now sterile, but were
habitable by terrestrial microorganisms, | submit we should still be extremely
ceutlous In ofr exploration. The Introduction of terrestrial life to such a
habitat would be bound to lead to wery large perturbations of planetary
chemistry, of a character which Is unpredictable beth In itself and with
respect to the presently unforeseeable ut! lization of planetary resources

that future technology may bring about. If we bring terrestrial lffe to Mars

Su9qq 1-3)
Br. N. E. Gibbons October 15, 1963
Page 2

and It can survive there, | believe it should be a matter of deliberate
forethought as to the projected consequences rather than an Inadvertence
arising out of our momentary Impatience.

1 am not sure precisely which documents Dr. Kellogg has furnished, slhtough
| as feniller with many of his writings and have great respect for his
authoritative position In this field. i would urge you to bring to the
attention of your coreespondents the considerations which are sumerized In
the enclosed note. {f these coples are not sufficient | will be happy to
furnish more of thea.

Sincerely yours,

Joshue Lederberg
Professor of Genetics

Enciesure: % coples of
Lederberg, J. and C. Sagan, 1962. Microenvironments for life
on Mars. Proc. Nat. Acad. Sci. 48: 1473675.