Searching for Signs of Life
Exactly what kinds of compounds could signal the presence
of life? Certainly water would be first on the list. From
geologic clues, scientists are convinced that water once existed in
equilibrium with the atmosphere on the surface of Mars. Water currently
existing on Mars is primarily in the solid or vapor state due to the
low temperature and low atmospheric pressure on Martian surface.
(12) Other compounds then rise to the top of the list. The
identification of carbonate and sulfate deposits could signal the
possibility of a past water source. In Earth's environment,
carbonate deposits are the result of aqueous sedimentation. It is
hypothesized that perhaps fossilized microorganisms may also be found in the
carbonate deposits.(8) Some scientists hypothesize that amino acids may be
present on or just below the Martian surface. On the surface,
conditions are highly oxidizing and would be hostile to organic
molecules. Some scientists anticipate that by drilling just below the
surface, the chance of finding protein residues, amino acids, would increase.
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Metal Carbonates |
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Phenylalanine |
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Phenylalanine is an amino acid that is present in many proteins. The possible identification of the existence of amino acids on or near the surface of Mars would yield strong evidence for the possibility of past life on the planet. This amino acid has multiple functional groups including a phenyl group attached to the basic backbone of the acid. The molecular model may be viewed on the right. The most predominant Raman signal from Phenylalanine occurs at 1000 cm-1. This stretch is the result of the stretch of the benzene ring (ring breathing) and is a key marker for this amino acid. (8) The diagram below illustrates a ring breathing mode for phenylalanine.
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Glycine |
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In addition to these simple chemical species, complex molecules such as chlorophyl or even entire organisms such as cyanobacteria emit very specific, identifiable Raman spectra. (2) The spectrophotometer used for these missions must be able to withstand the vigor of interplanetary travel as well as function robotically on a remote planet. Click on "The Raman Spectrophotometer" for more information. |