SUBSURFACE ALTERNATIVE. “Based on the studies cited above, an additional mechanism supporting subsurface life could be direct organic synthesis induced by Galactic cosmic rays-induced secondary particles, especially muons at greater depths. There is experimental evidence of the formation of amino acid precursors on exposure to high-energy particles. This mechanism could be especially important in the case of comets, as cosmic ray-induced ionization is believed to be the main driver of cometary organic chemistry.”
https://royalsocietypublishing.org/doi/10.1098/rsif.2016.0459