Abstract
I need a “tricorder”—the convenient, hand-held device featured on Star Trek that can detect life forms even from orbit. Unfortunately, we don't have a clue how a tricorder might work, since life forms don't seem to have any observable property that distinguishes them from inanimate matter. Furthermore, we lack a definition of life that can guide a search for life outside Earth. How can we find what we can't define? An answer may lie in the observation that life uses a small, discrete set of organic molecules as basic building blocks. On the surface of Europa and in the subsurface of Mars, we can search for alien but analogous patterns in the organics.
Highlights
Ineed a “tricorder”—the convenient, hand-held device featured on Star Trek that can detect life forms even from orbit
PLoS Biology | www.plosbiology.org might be like water, hard to define phenomenologically, but easy to define at the fundamental level
There are only two properties that can determine if an object is alive: metabolism and motion. (Metabolism is used here to include an organism’s life functions, biomass increase, and reproduction.) All living things require some level of metabolism to remain viable against entropy
Summary
Ineed a “tricorder”—the convenient, hand-held device featured on Star Trek that can detect life forms even from orbit. We don’t have a clue how a tricorder might work, since life forms don’t seem to have any observable property that distinguishes them from inanimate matter. We lack a definition of life that can guide a search for life outside Earth. How can we find what we can’t define? An answer may lie in the observation that life uses a small, discrete set of organic molecules as basic building blocks. On the surface of Europa and in the subsurface of Mars, we can search for alien but analogous patterns in the organics
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