  We demonstrate for the first time that Galactic cosmic rays with energies as
high as 1e10 eV can trigger a cascade of low-energy (< 20 eV) secondary
electrons that could be a significant contributor to the interstellar synthesis
of prebiotic molecules whose delivery by comets, meteorites, and interplanetary
dust particles may have kick-started life on Earth. We explore the relative
importance of low-energy (< 20 eV) secondary electrons--agents of radiation
chemistry--and low-energy (< 10 eV), non-ionizing photons--instigators of
photochemistry. Our calculations indicate fluxes of 100 electrons/cm2/s for
low-energy secondary electrons produced within interstellar ices due to
incident attenuated Galactic cosmic-ray (CR) protons. Consequently, in certain
star-forming regions where internal high-energy radiation sources produce
ionization rates that are observed to be a thousand times greater than the
typical interstellar Galactic ionization rate, the flux of low-energy secondary
electrons should far exceed that of non-ionizing photons. Because reaction
cross-sections can be several orders of magnitude larger for electrons than for
photons, even in the absence of such enhancement our calculations indicate that
secondary low-energy electrons are at least as significant as low-energy (< 10
eV) non-ionizing photons in the interstellar synthesis of prebiotic molecules.
Most importantly, our results demonstrate the pressing need for explicitly
incorporating low-energy electrons in current and future astrochemical
simulations of cosmic ices. Such models are critically important for
interpreting James Webb Space Telescope infrared measurements, which are
currently being used to probe the origins of life by studying complex organic
molecules found in ices near star-forming regions.
