planning for the Viking Mars Missions in the early 1970's, NASA
discussed a wide range of experiments
for detecting life on Mars, including ones which would discover
photosynthesis, proteins and enzymes. Finally they decided
on using five different ways to detect carbon-based, oxygen-breathing,
life. They were:
Chromatograph Mass Spectrometer - this
experiment was intended to detect and identify organic molecules
in the Martian soil, such as formaldehydes, using the then
new science of mass spectroscopy.
This experiment used samples from the topsoil, obtained
by a sample chute which placed them in a chamber. The chamber
had been tested during the flight to Mars, to ascertain the level
of contamination from Earth and the measurements were made against
this known background.
experiment did not detect any organic molecules which could have
indicated waste matter from living organisms.
Exchange Experiment - this would
analyze gases, given off from Martian soil, to look for biological
by-products. The soil sample was sealed in a container and
the Martian atmosphere was replaced by inert helium gas.
Then a fine liquid suspension containing nutrients (including
ascorbic acid) was introduced and a number of gas samples were
taken for chemical analysis. Variations in temperature,
humidity, and incubation time were made to different samples and
one was sterilized by heating.
was a very rapid liberation of oxygen measured when the low humidity
variation was carried out, but this soon halted. The oxygen
reaction was not affected by heating to 145 C (293 F). Whether
it took place in the light or the dark made no difference to the
reaction. When samples were incubated for several months,
this too had no effect on the strength of the reaction.
After three days, the soil was soaked in water and the analysis
repeated. This time, a third of the carbon-dioxide
present was absorbed into the water and soil immediately, and
the oxygen level decreased. After incubation, the samples
slowly released carbon-dioxide until the original balance was
achieved and the reaction ceased.
Release Experiment - this
used tagging of the nutrients by radioactive carbon, in order
to trace any absorption and subsequent excretion of them by living
organisms. Martian soil samples were taken and sealed
into containers with uncontaminated Martian air. Water
vapor and radioactively-tagged nutrients were added to the samples
and incubated for up to 52 sols (martian days). One of the
samples was sterilized and two were heated to 50 C (122 F).
The radioactivity being released from the soil was measured with
a Geiger counter and the readings compared with control samples
of Earth soil, under simulated Martian conditions.
the unsterilized samples the rapid increase in radioactivity level,
followed by a leveling off, was the same as for the Earth soil.
When sterilized, the soil did not release any radioactivity, again
this was the same as for Earth soil. Heat treatment at 50
C (122 F) for a prolonged time reduced radioactivity detected
in both Martian and Earth situations.
Release Experiment - this experiment
assumed that any life-form would need to breathe in carbon-dioxide
gas from the atmosphere, to incorporate carbon into its own structure.
It would detect carbon molecules that had been assimilated by
the organisms. The sealed chamber containing Martian soil,
was lit to simulate Martian day and night. Small quantities
of radioactive carbon-dioxide and carbon-monoxide were introduced,
in similar CO2
to CO proportions as Martian air. Again, water-vapor
was used to stimulate growth.
were incubated for five days, at between 8 C (46 F) to 26 C
(79 F), with simulated Martian days. Then radioactive gas
was extracted from the chamber and the soil analyzed. This
was done by heating the soil to 635 C (1175 F), to release carbon
atoms from the incinerated organic compounds. The gases
released from the burnt soil were then filtered and burnt to produce
carbon-dioxide gas again, which was passed by a Geiger counter,
so that radioactive carbon atoms could be counted.
results of seven, of the nine successfully carried out experiments,
showed small peaks of radioactive carbon atoms. These readings
could indicate a very low level of biological activity.
Lander Imaging -
images, to a resolution of centimeters
at a few meters away from the landers, were also examined to look
for signs of Martian life. Colonies of organisms might
provide a pattern which would change over time and weather conditions.
Animal tracks might be seen. The system of scanning used
to take the images would probably not have detected any fast-moving
entity. The images were studied and analyzed with the help
Viking team did not find any evidence of biological activity from