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Department of Genetics
Febr. 23, 1959

Or. Rithard Davies

Jet Propulsion Laboratories
California Institute of Technology
Pasadena 4, California

Dear Dick:

A propos the Cytherian atmosphere, some useful figures are in Hutchinson's
chapter in THE E@RTH AS A PLANET. Fossil carbon adds up to 18 kg/cm® ; atmospheric
COz is 460 mg/cm™, for a ratio of about 40,000:1. Hess reports the Cytherian
atmosphere as be/lng about 500X richer in co¥ than ours. 1 am not clear whether
this can be a measurement of the total atmospheric content, or only that part
above the cloud mass. The terrestrial atmosphere contains about 1:3000 C0e ; the
Cytherlan atmosphere would have to have a substantial cpmponent at 10 atm. or higher
pressure for it to contain an amount of COo equivalent to the total carbonate
sedimented on earth. Perhaps It does.

The blosphere may contain bard ee Pe GBunhhaRexGRe thee oc S camuinakenaxzex

of which perhaps 1-10 pc. is 'living'. This would
be roughly comparable to atmospheric C0zg on earth, and considerably less gaya than
Venus by this estimate. In any case, | don't see how one can draw any paxkkeukka
particular inferences, The biosphere Is only a small part of the total carbon, and
whether the rest Is locked away as carbonate sediments or as atmospheric COa seems
to me to depend more directly on other factors than the metabolism of the biosphere.
(1 should have stressed that 'fossil' carbon includes 2-3X as much carbonate as
reduced carbon).

StIl] on Venus, you might dom us a great service for the next meeting if you could
get someone to give us a more critical appraisal of the temperature profile. Is the
200° estimate highly plausible, and does it necessarily apply to the surface or to
some layer perhaps just beneath the clouds, or above them for that matter’ Hess nas
an oblique comment about possible ‘electric’ rather than thermal activation of the
emitting layer-- what does that mean? If you could get someone to review what the
earth would lé@e like from Venus by inference from the same methéds, we might have
a better perspective.

| expect you walked off, inadvertently, with my potential dlagram-- unhapplly that
is my only copy. I am sure that this does not represent a minimum-energy path for
e collision, and possibly not even for soft landing. The line Integral you're thinking
of would apply to a conservative system, but I'm adding up the labsolute! values for
each step, since the rocket has to do work ammkka equally to accelerate or decelerate.
The paths I've pictured would be: @ from earth's surface to solar orbit at 1 A.U. (=
escape from earth's field), @ circular orbit at 1 A.U. to circular orbit at 1.52 AU.
(= co-orbital with Mars and at equal velocéty (© work to decelerate In Mars" fleld («
escape from Mars). A gaxkag grazing orbit, i.e., ellipse with apahelion at 1.52 A.U.
would reduce(b) to about half, and if the velocities were in the right sense, (©) might
also be partly reduced, { haven't worked this out carefully, and would be grateful if
one of your experts could reduce the results to the simple graphical form Indicated.
This may not be terribly Important any more, but it would be Interested to see at a
glance what the energy cost of sarious missions was.