The announcement this week of the detection of liquid water
on Mars has come close on 4 decades after the arrival of the first Viking
landers at the red planet in 1976. The temperatures at the two original landing
sites of the Viking spacecraft in 1976 ranged between a high of -31°C and a low
of -84°C, so no liquid water would have persisted at the surface.
The Viking
probes had also carried out in situ biological tests of Martian soil, the
so-called Labeled Release Experiment, where an isotope-labeled nutrient was
applied to the soil to test for the presence of microbial life. An astoundingly
positive result for the uptake of the nutrient and hence extant life was
obtained; but it was quickly rejected on grounds of alleged uncertainties of
interpretation, as well as the lack of organic molecules detectable at the
landing site.
A year later, in1977, a major dust storm enveloped the planet and
H. Abadi and the present writer reported evidence of absorption properties of
the Martian dust that was consistent with the presence of aromatic
hydrocarbons. In 2012 a careful reexamination of all the Viking results of 1976
led to the conclusion that a positive detection of microbial life on Mars may
have been obtained at the time. This is a position that Gil Levin has firmly
held and defended against all his critics.Read More....