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, 2 (9), E302

What Is Life--And How Do We Search for It in Other Worlds?


What Is Life--And How Do We Search for It in Other Worlds?

Chris P McKay. PLoS Biol.


If there is life on distant worlds, how would we go about finding it?


Figure 1
Figure 1. Water on Another World
A Mars Global Surveyor image showing Nanedi Vallis in the Xanthe Terra region of Mars. The image covers an area 9.8 km ×18.5 km; the canyon is about 2.5 km wide. This image is the best evidence we have of liquid water anywhere outside the Earth. Photo credit: NASA/Malin Space Sciences.
Figure 2
Figure 2. Comparison of Biogenic with Nonbiogenic Distributions of Organic Material
Nonbiological processes produce smooth distributions of organic material, illustrated here by the curve. Biology, in contrast selects and uses only a few distinct molecules, shown here as spikes (e.g., the 20 l-amino acids on Earth). Analysis of a sample of organic material from Mars or Europa may indicate a biological origin if it shows such selectivity.

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