Pathfinder is now enroute to Mars for a July 4, 1997 landing.
Its lander is equipped with a camera having better color and spatial
resolutions than did Viking's. It is possible that a close-up picture of a
rock might show clear evidence of biological colonies. A search for such
evidence should be a Pathfinder priority.
2. Use Hubble Telescope. The Hubble Telescope
should be used to seek evidence of large areal changes in the color and
patterns of the martian surface and seek to correlate them with
atmospheric water vapor and climatic seasons. Useful images that already
may exist in the Hubble files should be compared.
3. Seek Chirality in Mars Samples. Perhaps the
surest robotic means for unequivocal distinction of biological from
chemical reactions is a test for chiral activity. For some yet unknown
reason, or by chance, when the first living cells came into existence
their enzymes were chiral specific. They catalyzed protein-building
reactions with L-amino acids only. They had a similar preference for
L-carbohydrates over D-forms. Throughout the evolution of all living
forms, these preferences have been genetically transmitted. This
peculiarity of living systems provides a ready means of distinguishing
them from chemical reactions. Chemical reactions, without the intervention
of man, cannot distinguish between L- and D-isomers. On the other hand,
all known life forms utilize and make virtually only the L-form of amino
acids. Thus, were a sample of martian soil to react with one chiral isomer
of a compound and not the other, the biological nature of the reaction
would be established. A simple, small, low-cost experiment has been
proposed90 which would separately add L-cysteine and D-cysteine
(FIG. 11) to respective small ovens in the Surveyor '98 Thermal and
Evolved Gas Analyzer (TEGA). TEGA will measure CO2 evolved when
samples of martian soil placed in them are heated. Were the amount of
CO2 evolved from the oven containing one isomer of cysteine to
exceed the amount from the oven containing the other isomer significantly,
the case for life would be confirmed.
4. Protect Health and Environment. Samples of
martian material should not be returned to Earth before a thorough
evaluation of possible hazards. The simple test for chirality could
provide a warning of potential hazards to health and environment before a
sample from Mars is returned to Earth. An upgraded version of the LR
experiment might be added to an upcoming martian lander. This experiment
would differ from the original in that the chiral isomers would be offered
separately. The advantages of this approach are that it builds on the
proven technology of Viking and that the Viking results provide relevant
data for comparison. In addition, it could permit testing under controlled
environmental conditions. Many other means of inquiry would follow a
positive test to begin studies of comparatively biology.
5. Continue SNC studies. The ongoing appraisals
of the meteorites reported to contain evidence of martian microbial life
may confirm the conclusion reached herein. In particular, if EETA79001 is
validated as to both its Mars origin and its evidence of microbial life,
this would constitute such confirmation.
In the 45 years since I first developed the radioisotopic
method for detecting microorganisms, I have been fortunate in my
assistants. This variously composed team total nearly half a hundred
people. I have acknowledged each in the more than 50 published papers many
have co-authored with me, and I now thank them collectively. I do want to
mention several individuals. Dr. Patricia Ann Straat, my Viking
Co-Experimenter, was my right arm at Biospherics during the 10-year period
covering the Viking mission. She was essential to the success of the LR
experiment. Her predecessor was Mary-Frances Thompson who did a splendid
job overseeing our early laboratory efforts. Engineer George Perez was
able to take my sketchy concepts for the early instruments and reduce them
to excellently functioning metal. TRW, Inc. converted the early
instruments into the faultlessly performing Viking LR instruments. I
particularly want to thank my son, Dr. Ron Levin, a physicist, for his
constant support of the LR life interpretation, his help with the
water-on-Mars issue, and in extracting the Mars images from the JPL
The bulk of the work reported on herein was funded by
a series of NASA Headquarters contracts with the companies where I was
employed: Resources Research, Inc., Hazleton Labs, Inc., and Biospherics
Incorporated. Since 1979, my efforts in analyzing the Viking Mission
results have been supported by Biospherics. I would like to thank its
Board of Directors for indulging my commitment to this issue and for the
1. McKay, D.S., E.K. Gibson, K.L. Thomas-Keptra, H. Vali, S.
Romanek, S.J. Clemett, X.D.F. Chillier, C.R. Maechling, and N. Zare,
"Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian
, 273, 924-930, 1996.
2. "Martian Lanuch Pads,"
S&T's Weekly News Bull
Sky Pub. Corp., 1, 11, Nov. 96.
G.V.," Detection of Metabolically Produced Labeled Gas: the Viking Mars
, 16, 153-166, 1972.
Levin, G.V. and P.A. Straat, "Labeled Release - An Experiment in
Radiorespirometry", Origins of Life
, 7, 293-311, 1976.
5. Miller, S.L., "A Production of Amino Acids Under
Possible Primitive Earth Conditions,"
, 117, 528,
6. Levin, G.V. and P.A. Straat, "A
Reappraisal of Life on Mars,"
Proc.. NASA Mars Conf
., Nat. Ac.