Geoscience Reference
In-Depth Information
The prime concern of hardware contaminating Mars derives from incomplete
spacecraft sterilization of some hardy terrestrial bacteria (extremophiles) despite
best efforts. Hardware includes landers, crashed probes, end of mission disposal
of hardware, and hard landing of entry, descent, and landing systems. This has
prompted research on radiation-resistant microorganisms including
Brevundimonas
,
Rhodococcus
,
Pseudomonas genera
,and
Deinococcus radiodurans
survival rates
under simulated Martian conditions. Results from one of these experimental
irradiation experiments, combined with previous radiation modeling, indicate that
Brevundimonas
sp
.
MV.7 emplaced only 30 cm deep in Martian dust could survive
the cosmic radiation for up to 100,000 years before suffering 10
6
population
reduction. Surprisingly, the diurnal Mars-like cycles in temperature and relative
humidity affected the viability of
Deinococcus radiodurans
cells quite severely.
In other simulations,
Deinococcus radiodurans
also failed to grow under low
atmospheric pressure, under 0
ı
C, or in the absence of oxygen.
8.5.3
Reanalysis of the Viking Labeled Release Experiments
One of the designers of the Labeled Release experiment, Gilbert Levin, believes his
results are a definitive diagnostic for life on Mars. Levin's interpretation is disputed
by many scientists. A 2006 astrobiology textbook noted that with unsterilized
terrestrial samples, though, the addition of more nutrients after the initial incubation
would then produce still more radioactive gas as the dormant bacteria sprang into
action to consume the new dose of food. This was not true of the Martian soil; on
Mars, the second and third nutrient injections did not produce any further release of
labeled gas. Other scientists argue that superoxides in the soil could have produced
this effect without life being present. An almost general consensus discarded the
Labeled Release data as evidence of life, because the gas chromatograph and mass
spectrometer, designed to identify natural organic matter, did not detect organic
molecules. The results of the Viking mission concerning life are considered by the
general expert community, at best, as inconclusive.
In 2007, during a Seminar of the Geophysical Laboratory of the Carnegie
Institution (Washington, D.C., USA), Gilbert Levin's investigation was assessed
once more. Levin still maintains that his original data were correct, as the positive
and negative control experiments were in order.
Moreover, Levin's team, on 12 April 2012, reported a statistical speculation,
based on old data (mentioned above and below in the text) - reinterpreted math-
ematically through cluster analysis - of the Labeled Release experiments, that may
suggest evidence of extant microbial life on Mars. Critics counter that the method
has not yet been proven effective for differentiating between biological and non-
biological processes on Earth so it is premature to draw any conclusions.
A research team from the National Autonomous University of Mexico headed
by Rafael Navarro-González concluded that the GCMS equipment (TV-GC-MS)
used by the Viking program to search for organic molecules may not be sensitive
Search WWH ::
Custom Search