cr -/

Please reply to Genetica Bldg.

Dr. Fred L. Whipple
Harvard College Observatory
Cambridge, Masg.

Dear Dr, Whipples

T have lately become interested in the much mooted queation of prebiotic
synthesis of organic (carbonaceous) molecules, At least since Oparin's first
boek there has, of course, been much attention given to the activation af
the simple hydrides by ulgraviolet light and related processes in the |
atmosphere of the already farmed earth, Without Wishing to diminish the
importance of these processes, I have however been wondering if such
synthesia might be occurring on a much grander scale as part of the evolupion
ef the interstellar grains,

Your own work on the composition of comets has particularly fascinated
me, es it furnishes some hope of eventual verification of this model, insofar
as the satellite program may lead to the retrieval of interplanetary dust
for chemical analysis — except for the lightest components, the surface
of the moon will be of course an abundant source.

P%dd'H

My main question 1s your present thought of the molecular chemistry of
the interstellar grains (and of the cometary substance which, I gather, you i
would consider to be of comparable composition). In your "Comet model, IT.", Ty
1951, you wrote that "Lacking at present sufficient information to estimate °
the frequency distribution of the various molecules of H, C, N, and 0 the .
writer has arbitrarily assumed that the major mass is in the forn of CH, » NHg gy
and H,0." Does this then leave open the plausible possibility of the
existénce of much larger molecules as an appreciable part of the total conpo~
sition? The reduced abundance of H in the canet perhaps makes this more
plausible for the canet than for the intersteller grain,

My comprehension of the astrophysical literature is bound te be shamefully
naive and uncritical, but I cannot readily decide whether the chentlatry of
larger molecules has simply been overlooked (perhaps intentionally on account
of its complexity or inaccessibility) or whether there are good reasons to
limit discussion to the simple hydrides. I an speaking, of course, of situations
where the particle temperature and the radiation flux are relatively small.

When interstellar grains are referred to as aggregates of H C N and 0 I can't
help wondering if they might not be immense macromolecules,

If you can still furnish reprints of your Comet-Model and related papers,
I would be most grateful for them, as I will have to spend more time on them
than I can conveniently do in the library.

Yours sincerely,

Joshua Lederberg
Chairman, Dept. of

Medical GWnetics