Sputtering of Presolar Grains via Galactic Cosmic Rays in the Interstellar Medium.

The sputtering rate of presolar silicon carbide grains due to galactic cosmic rays has been computed for their experimentally deduced lifetimes (∼1 Gyr) in the interstellar medium. An ion target simulator, SDTrimSP, was used to model the sputtering of interstellar grains with varying sizes and thicknesses of the ice mantle formed around the grain during their journey through the interstellar medium. Temperature, composition, and density for four different types of molecular cloud environments (quiescent, low-mass young stellar objects (YSOs), intermediate-mass YSOs, and high-mass YSO weak processing) considered indicate the sputtering rate on the mantle ice composition depends on water composition to a certain extent. The model simulations indicate galactic cosmic ray(s) with an energy range from 10 MeV to 1 GeV are just capable of sputtering/destructing ∼13%–15% of the grain itself. This value, stretched over 1 Gyr is not as significant as the other destruction processes and therefore can be classified as a minor destruction process. The effect of galactic cosmic rays on the ice mantle and core is also noted with particular emphasis on amorphization/recoils generated inside the SiC core and their distribution within the grain. [ABSTRACT FROM AUTHOR]