astrochem'org the astrochemistry lab at NASA Ames Research Center

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(image by Andy Christie for Scientific American
July 99)
astrochem.org the astrochemistry lab at NASA Ames
Research Center
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The search for life in the Solar System We may
get lucky
Image of Europa from ase.jpl.nasa.gov/
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but the search for life in the Solar System is
far more likely to be the search for organic
biomarkers
Amino acids
Sugars
Substituted aromatics
Fatty acids
Nucleobases
Nitrogen containing heterocycles
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• Molecules that look like biomarkers
• (but may not be convincing indicators of life)
• Various aromatics (invoked in martian meteorite)
• Amino acids (components of proteins)
• Fatty acids (components of membranes)
• Sweeping generalizations

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We make a little bit of space in our laboratory,
and see what happens.
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(image by Andy Christie for Scientific American
July 99)
Interstellar ice photochemistry
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Drawing a line in the (Martian) sand
No more free molecular species, commonly used in
geochemistry i.e., terpenes or PAHs
Unlessyou see something way out of equilibrium
or non sensical i.e.,
High ee Only one (or a very narrow distribution
of) chain lengths or functional groups when many
are expected.
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Drawing a line in the (Martian) sand
Definitely No enzymatic tests that rely on
their biochemistry being the same as ours. Dont
assume their chromophores will be the same as
ours i.e., Chlorophyll
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Keeping an open mind
On the other hand, we dont want to miss life
because its basic components are different from
ours. Would we get a detection if they used
different bases, different sugars, and had the
opposite chirality of amino acids?
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In summary we must be
Knowledgeable open-minded without being
credulous
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In summary we must be
Knowledgeable open-minded without being
credulous
much like the Astrobiology Exobiology panels to
whom I am grateful for financial support
Jason Dworkin (GSFC), Scott Sandford, Louis
Allamandola (Ames)
SETI
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XA
Liu et al., Science (2003) 302, 868.
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XT
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Alternative sugars, i.e., allopyranose
Eschenmoser (1999) Science, 284, 2118
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HO3P-
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FMN, coenzyme in certain oxidation-reduction
reactions in the body
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chirality
(non-super imposable mirror images)
(almost) All the chiral amino acids in living
things are left handed, and there is also a bias
for left handed amino acids in meteorites. The
reason(s) for this is not yet clear.
Cronin, J. R., Pizzarello, S. (1997) Science
275, 951-955.
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