<title>Microbial life detection with minimal assumptions</title>

To produce definitive and unambiguous results, any life detection experiment must make minimal assumptions about the nature of extraterrestrial life. The only criteria that fits this definition is the ability to reproduce and in the process create a disequilibrium in the chemical and redox environment. T he Life Detection Array(LIDA), an instrument proposed for the 2007 NASA Mars Scout Mission, and in the future for the Jovian moons, enables such an experiment. LIDA responds to minute biogenic chemical and physical changes in two identical “growth” chambers. The sensitivity is provided by two differentially monitored,electrochemical sensor arrays. Growth,in one of the chambers,alters the chemistry and ionic properties and results in a signal. This life detection system makes,minimalassumptions; that after addition of water the microorganism replicates and in the process will produce small changes in its immediate surroundings by consuming, metabolizing, and excreting a number of molecules and/or ionic species. The experiment begins by placing an homogenized split-sample of soil or water into each chamber, adding water if soil, sterilizing via high temperature, and equilibrating. In the absence of any microorganism in either chamber, no signal will be detected. The “inoculation” of one chamber with even a few microorganisms which reproduce,will create a sufficient disequilibrium in the system (compared to the control) to be detectable. Replication of the experiment and positive results would lead to a definitive conclusion of biologically induced changes. The split sample and the “nanogram” inoculation eliminates chemistry as a causal agent. Keywords: Mars, Astrobiology, Life Detection, Microbial Growth 1.,INTRODUCTION “The minimum,requirements for us to recognize an object as living is that it…. or some members,of its kind should… reproduce.” (Richard Dawkins)