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Polarized Starlight and the Handedness of Life

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Figure 6. Circularly polarized lightClick to Enlarge Image

Whereas amino acids produced by inorganic reactions are equally split between two mirror-image versions, the amino acids found in living things are almost universally "left-handed." The origin of this biological homochirality, as it is called, has been clouded in mystery, but a group of astronomers may have stumbled on the answer. They found that the light passing through large parts of the cosmos is sometimes circularly polarized in one direction. Such radiation can preferentially destroy one version of the amino acid molecules that form in space along with other complex organic compounds. A similar occurrence five billion years ago may have seeded the solar system and the early earth with a lopsided mix of amino acids, which would have favored one handedness over the other when life evolved from these organic molecules.

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