Possible and False Biomarkers from Space

Abstract

The Search for life in the Solar System is one of NASA's main goals for the coming decade. We may never observe alien life directly; we or our robotic craft may always be removed from it by many years, or meters of crust. If we do find evidence of Life elsewhere in the Solar System it will probably be in form of chemical biomarkers, quintessentially biological molecules that indicate the presence of micro-organisms. What molecules would be truly indicative of alien life? Chlorophyll fragments, which are often used by geochemists are probably far too specific. Simpler molecules, such as fatty acids, amino acids and nucleo-bases might seem to be biomarkers, but they can form non-biotically in space. Alkyl substituted aromatics in ALH 84001 have been invoked as biomarkers, but they are not strong evidence in and of themselves. Understanding the range of nonbiological organic molecules which could act as false biomarkers in space is a prerequisite for any reasonable search for true biomarkers on other worlds. When simple organics arrive at the surface of a body like Europa, either from below or from space, how long do they survive and what do they make? How can we distinguish these from real biomarkers? In this talk I will present some ideas about what might be useful qualities to consider in a potential biomarker, and will ask for advice from the attendant geochemists.