June 25, 1964

Dr. &. B. Leighton

Norman Bridge Laberatery of Physics
Califoraia Inetitute of Technolegy
Pasadena, California

Dear br. Leighton:

The Space Science Board of the National Acadeny of Sciences, at the
request of the National Aeronmutics end Space Aduinistration, has
undertaken to review the scientific ains and methodology of the

seareh for extraterrestrial life. In order te ecenonise on the

time of scientific specialiets, we are departing frou the toe cus-
tomery sultiplicstion of large scale meetings end will rely to the
largest peesible extent on communication by wail and on reference

te the literature. A Working Group has accepted the burden of draft-
ing 4 summary report. We expect te use contributed material just as
received from or enended by the contributors as supporting decusentation.

Uatil recently, NASA's major efferts tn exeblology were focussed on
missions involving vehicles of the Atias end similar types. Prospects
with these rockets are limited, at best, te the landing of a few pounds
of iustruments on Mars, with a ainisus of supporting pewer end teleastry.
However, the rapid progress of the Saturn systems now makes it possible
to consider a totally different kind of program, in which payloads of

wp to 20 tone aight be landed on Mars. Yhe complexities of such afesions
end the importance of early planning are self-evident, even though 1969
or 1971 are the earliest conceivable dates on which these attenpts

aight be made.

Ageinst this background, we ask you specifically to consider the
eesignuaent described below.

As a basis for further eelentific and engineering study, we are

' attempting to enumerate the funetione which should be embodied in
an analytical system for bielegical study of Mere - that is, the
characteristics of an ensembic of selentifie instruments to be
lended on the planet. At the same tine, we wish te aseure ourselves
that we sre giving appropriate priority te the invesitgations to be
undertaken and to the varieus meane of pursuing then. ‘The selection
De. BR. 3B. Leighton June 2S. 1964
Page

of these is tentative and subject te mech revision, but « begioning
is needed.

The probless under consideration ere:

1. The diegnesis of the presence of life on Mere, under
various asewsptions of the extent ef ite evolution
aad ef its divergence from the terrestrial systen.

2. If life te present, the characterization of its
composition, metabolion, ecolegy, and btetory.

3. The characterisation ef the MNertian exvirensset, par-
ticularly but net exclusively fa conmsction with
evidence for existing life and for the possibility
of the colenization of Mars by terrestrial organiens.

Special emphasis has been placed om the exanination of soil for
wicrobiel activity, and fecilities fer acquiring eamples of it
have already been considered. If other kinds of easples are
impertent, what are they and how wight they be acquired for
analysis? The present discussion centers o Per went 1

   

with telewetry beck to earth.
outeide present consideration.

Of a series ef instrumental approaches, partly summarized on the
atteched List, we would especially ask your detailed coment on:

fV Pictures

Principally we vould want yeur best judgenent on the relative
interest that this method should attract in dealing with the basic
problems se stated abeve. Uagineering details should be ef sinizam
concera te you, though any renarke yeu may have on the possibility
end directions of uinisturising the {netrusentation, if necessary,
would be welcome. Move important is your seseesnent of the ways {a
which the instresent (or technique) can contribute to solution of
these problems; the interpretability ex eubiguity of ite indications
and quantitetive steatenents on present end expected limits ef sen-
sitivity; censtraiate on type aud size of senples, end requirexeats
for sample preparation end treatuent.

Experience has shown that some seemingly abeurd tdeas need careful
cousideration, and precisely fer this reason, several instresentel
sppreaches are listed although a superficial consideration would
tend to exclude then.

A prelininary draft of a acte on "Signs of Life” is attached te
help provweke the passionate response to which we leck ferward. A
capoule swunary of our current knowlaige ef Mars, which is gersane
De. BR. B. Leighton dune 25, 1964
Page 3

to the topic, is also enclosed; «a sere detailed report on "The
Atmospheres of Mars and Venus" will be forvarded to you under
seperate cover.

De. Joba McCarthy, of Stanford University, has agreed to receive
and prepare your comments for distribution te the Working Group;
please send then te: Spece Science Board, National Acadesy of
Seleaces, 800 Welch Read - Suite 214, Pale Alte, Califernte,
telephene: 324-0091. Additional information relating te this
effort will be previded as may be necessary.

I hope this letter will elicit your interest, and hopefully, sone
prelinisary comments before the preparation of the firet draft
of the report on July 15.

Very truly yours,

Joshua Lederberg

Jf $4
enc lesures

ce: Dr. John MeCerthy
Sr. BD. G. Rea