Tiny Microbes Inspire Modern Microbe Hunters to Think Big

Is life on Mars? Indisputably, the answer is yes; unfortunately, we delivered it there. In fact, every spacecraft sent to the Red Planet is allowed to carry a small amount of terrestrial contamination onboard, including hardy endospore-forming bacteria capable of withstanding severe conditions in space. How will future astrobiology missions searching for indications of life—past or present—disentangle the signature of terrestrial contaminants from potentially native life forms? While we can do a better job at reducing the viable bioburden on spacecraft by aggressive sterilization methods, it adds substantial costs to missions and limits the type of instruments that can be carried (e.g., computers don’t like to be autoclaved). Even a fully aseptic spacecraft would still be littered with microbial debris—biosignatures thatmight be indistinguishable from samples acquired in a precious scoop of Martian soil. Knowing this, perhaps we must accept the inevitable contamination issue and focus instead on identifying our own signal through intentional tagging and traceability. Systematic approaches using synthetic molecular barcodes or inert fluorescent particles would at least tell us which samples are fouled and which can be trusted. The detection of life beyond Earth will someday send shockwaves through popular culture and reconfigure humanity’s understanding of the universe. We must ensure that such a discovery will not be corrupted or confused by a false signal. Digging for Ancient Pathogens