Nonlinear analysis of the Viking lander 2 labeled release data

During Viking missions (Mars, 1976) experiments to detect signs of life were performed in the Martian soil. In particular, the Labeled Release experiment (LR) monitored the evolution of radiolabeled gas after injection of a 14C-labeled nutrient mixture. Recently, JD Miller et al. (2002) analyzed the previously unrecognized fluctuation in radiolabeled gas with a period equal to 1 Sol. These periodic oscillations resulted correlated with the periodic oscillation in the temperature inside the test cell where experiments were done. Possible interpretations were the result of a circadian rhythm of a putative Martian microorganism as well a simple chemical oscillation driven by thermal fluctuation. Here, we have performed a nonlinear analysis of high frequency fluctuation data of the released radiolabeled gas compared to the temperature fluctuation data inside the test chamber. Our results show that the structure of temperature signals (LZ = 0.272, Lyapunov = 0.382 ± 0.156, H= 0.694, CD = 3,020 ± 0.105) is completely different from the one of the releases radiolabeled gas (LZ = 0.469, Lyapunov = 0.480 ± 0.129, H= 0.21, CD = 3.821 ± 0.168), permitting to exclude that the latter might be provoked by a simple chemical oscillation triggered by thermal fluctuation. Moreover, gas release fluctuation data approached very well the one of biological processes (e.g. heart rate time series of a human neonate). Our results strongly support the hypothesis of a biologic origin of the gas collected by the LR experiment from the Martian soil.