Abstract
Glycolaldehyde (GLA), a two-carbon sugar precursor, has been detected in
multiple regions in our galaxy and on comets in our solar system. Impact
experiments conducted at the Experimental Impact Laboratory at NASA’s
Johnson Space Center have shown that samples of GLA and GLA mixed with
montmorillonite clays can survive impact delivery in the pressure range
of 4.5 GPa to 25 GPa. When extrapolated to amounts of GLA observed in
the comae and in situ on the nucleus of individual comets and assuming a
monotonic impact rate in the first billion years of solar system
history, these experimental results show that up to 1023 kg of cometary
GLA could have survived impact delivery, even if comets made up just
20% of the total impactor population. Substantial amounts of threose,
erythrose, glycerol, glycolic acid, and ethylene glycol would also have
been produced or delivered, depending on initial amounts and impact
conditions. During the era of heavy bombardment (~4.2 to
~3.7 billion years ago), when life may have been
developing on Earth, cometary impacts were likely prevalent throughout
the solar system. They would have delivered these sugar molecules to
Mars and to the icy moons of Jupiter and Saturn, providing additional
intriguing evidence that biomolecules would have been abundant on these
planetary bodies, too. The presence and availability of these
biomolecules under the right conditions may have driven prebiotic
chemical reactions that lead to, for example, ribose, the five-carbon
sugar in RNA. In short, because experimental evidence shows that GLA
survives impact, understanding impact delivery of biomolecules (in
general, and including amino acids) may be important for answering
questions about the origin of life as we know it. A diverse and
wide-ranging approach that includes not only practices of investigation
(i.e., experiments, observations, modeling) but also experiences and
perspectives of the investigators, will be key to addressing the issues
related to the origin of life on Earth and potentially elsewhere.