Organic input to Titan’s subsurface ocean through impact cratering

Titan has an organic-rich atmosphere and surface, with a subsurface, liquid water ocean that may represent a habitable environment. In this work, we determined the amount of organic material that can be delivered from Titan’s surface to its ocean through impact cratering. We assumed Titan’s craters produce impact melt deposits composed of liquid water that can founder in its lower-density ice crust, and estimated the amount of organic molecules that could be incorporated into these melt lenses. We used known yields for HCN and Titan haze hydrolysis to determine the amount of glycine produced in the melt lenses and found a range of possible flux rates of glycine from the surface to the subsurface ocean. These ranged from zero to 1011 mol/Gyr for HCN hydrolysis and from zero to 1014 mol/Gyr for haze hydrolysis. These fluxes suggest an upper limit for biomass productivity of ~103 kgC/yr from a glycine fermentation metabolism. This upper limit is significantly less than recent estimates of the hypothetical biomass production supported by Enceladus’s subsurface ocean. Unless biologically available compounds can be sourced from Titan’s interior, or be delivered from the surface by other mechanisms, our calculations suggest that even the most organic-rich ocean world in the Solar System may not be able to support a large biosphere.