LOWELL OBSERVATORY

FLAGSTAFF, ARIZONA
April 25, 1959

Dr. Joshua Lederberg
Department of Genetics
School of Medicine
Stanford University
Stanford, California

Dear Dr. Lederberg:

Here is the analysis of the feasibility of detecting organic
matter on Mars from a pwobe.

First the detection from a probe of NH bending and C=0 stretching
bands at 5 - 6 p is considered. Most of the energy from Mars at these
wavelengths will be thermal emission. I find that for an emissivity of
0.5 the energy received per cm from the whole of Mars at 100,000 miles
within a 0.1 yp band is 5 x 107” watts. Since lead selenide detectors at
liquid nitrogen temperatures can detect 1079 watts or less, from a detection
standpoint the test seems feasible. Telescope apertures of the order of
100 em“ would seem to yield adequate signal-to-noise ratios. The bands will
appear in emission since, as mentioned, the majority of the energy is
thermal emission. Some amount of surface discrimination may be possible,

particularly is larger telescope apertures can be used. Observation of &
these bands from the ground is prohibited poor atmospheric transmission and =
the small amount of energy. From a balloon this latter difficulty will be <
condiderably enhanced by restricted apertures available. «i

Another possibility I have consédered is detection of N-H and 0-H &

stretching bands at 3 p. This region is aggin messed up at ground level
by a water band. In a balloon this difficulty is eliminated. One expects
about 2 x lo-il watts/0.1 p from the whole of Mars in a 12-inch aperture.
@his would be detectable by uding a cooled lead sulfide cell. To obtain
resolution on the sueface a considerably larger aperture or a probe is
required.

‘bf o7

I have learned, partly to my chagrin, that carbonates have prominent
bands right at 3.4 microns. However, the presence of carbonates on Mars is
eliminated by the fact that their bands are not like the observed in that
there is nog appreciable absorption at 3.67 p. It is still further eliminated
in that carbonates have a very strong absorption at 3.9 m which is not
observed on Mars. However, I feel that, from the observations alone, one
can not be sure that the observed absopptions are produced by organic molecules.

I have enclosed the travel vouchers and my tickets.

Sincerely,

BL

William M. Sinton