Both
the Spirit and the Opportunity roving vehicles carry a
device called the Mössbauer Spectrometer, which is able to tell the difference
between two forms of iron in chemical compounds in the Martian soil and
rocks. If the Martian surface contains
H2O2 or other oxidizing agents, then a lot of the iron
should be in ferric, or oxidized form (Fe+3). However, if the Maritan surface is more
reduced, then a lot of the iron should be in the ferrous or reduced
form (Fe+2). Based on
initial reports, it appears that almost all of the Martian surface iron is
indeed in the ferrous form. If this is
confirmed, it will mean that the oxidant hypothesis used to explain the results
of the 1976 LR experiment is entirely incorrect. Mars may indeed harbor microorganisms, even today.
But the current Martian surface environment appears to be hostile to anything alive. Unlike Earth, Mars has no protective ozone layer to filter out the dangerous ultraviolet (UV) rays that break apart the organic molecules from which lifeforms are made. On the other hand, life forms, if present today, would be protected from UV if they live underground, or even inside or under a rock at the surface.
But what about the mystery of the Viking landers, which examined samples from the surface material itself? One possibility is that underground life may exist throughout the planet and that in hostile environments such as the Viking landing sites, microorganisms may undergo a process called sporulation, essentially a form of microbial suspended animation. On Earth, certain microorganisms can exist for millions of years as spores –not exactly alive, but not dead either. Given what we are learning from Spirit and Opportunity, we cannot dismiss the posibility that in the Viking LR experiment of 1976, a few spores were re-animated when exposed to the nutrients and the water injected into the soil sample. However, the definitive answer to the question of whether or not Mars harbors microorganisms awaits the delivery of sophisticated astrobiology instruments.