So what's up with all these positive detections?
Discussion from http://cmex-www.arc.nasa.gov/MarsEssy/life/life.htm:
"The most important result for the detection of life came not from
the biology experiment, but from the GCMS. It found no trace of any
organic compound on the surface of Mars. Organic compounds are known
to be present in space (for example, in meteorites), so this result
came as a complete surprise. The GCMS was definitely working,
however, because it was able to detect traces of the cleaning
solvents that had been used to sterilize it prior to launch. "The total absence of organic material on the surface made the
results of the biology experiments moot, since metabolism involving
organic compounds were what those experiments were designed to
detect. However, the results from the biology experiments were
sufficiently confusing to be worth examining. "To reduce the chance of false positives, the biology experiments
not only had to detect life in a soil sample, they had to fail
to detect it in another soil sample that had been
heat-sterilized (the control sample). Had terrestrial life
been tested with the Viking biology instrument, the following results
would have been expected:
|
| Response for Sample | Response for Heat-sterilized Control |
| GEX |
O2 or CO2 emitted |
none |
| LR |
labeled gas emitted |
none |
| PR |
carbon detected |
none |
"If life was completely absent from Mars, as the GCMS results
suggested, these should have been the results from the biology
experiments:
|
| Response for Sample | Response for Heat-sterilized Control |
| GEX |
none |
none |
| LR |
none |
none |
| PR |
none |
none |
"In highly simplified form, these were the actual results from
Mars:
|
| Response for Sample | Response for Heat-sterilized Control |
| GEX |
O2 emitted |
O2 emitted |
| LR |
labeled gas emitted |
none |
| PR |
carbon detected |
carbon detected |
"The fact that both the GEX and PR experiments produced positive results even with the control sample indicates that non-biological processes are at work. Subsequent laboratory experiments on Earth demonstrated that highly-reactive oxidizing compounds (oxides or superoxides) in the soil would, when exposed to water, produce hydrogen peroxide. Oxidized iron, such as maghemite, could act as a catalyst to produce the results seen by the PR experiment.
"Only the LR experiment appears to have met the criteria for life detection, and it does this rather ambiguously. When the nutrient was first injected, there was a rapid increase in the amount of labeled gas emitted. Subsequent injections of nutrient caused the amount of gas to decrease initially (which is surprising if biological processes were at work) but then to increase slowly. No response was seen in the control sample sterilized at the highest temperature (160C, 320F.) While there is still some controversy, the consensus opinion is that the LR results can also be explained non-biologically."