Revisiting the lifetime estimate of large presolar grains in the interstellar medium

Hiroyuki Hirashita, Takaya Nozawa, Ryosuke S. Asano, Typhoon Lee

Planetary and Space Science
In Press, Accepted Manuscript, Available online 22 February 2016

updated (Feb. 24)


“Some very large View the MathML source(>0.1μm) presolar grains are sampled in meteorites. We reconsider the lifetime of very large grains (VLGs) in the interstellar medium focusing on interstellar shattering caused by turbulence-induced large velocity dispersions. This path has never been noted as a dominant mechanism of destruction. We show that, if interstellar shattering is the main mechanism of destruction of VLGs, their lifetime is estimated to be View the MathML source≳108yr; in particular, very large SiC grains can survive for ∼1 Gyr. The lifetimes obtained for VLGs are comparable to the longest residence time derived for some presolar grains based on the cosmic-ray exposure time. However, most presolar SiC grains show residence times significantly shorter than 1 Gyr, which may indicate that there is a more efficient mechanism than shattering in destroying VLGs, or that VLGs have larger velocity dispersions than 10 km s−1. We also argue that the enhanced lifetime of SiC relative to graphite can be the reason why we find SiC among μm-sized presolar grains, while the abundance of SiC in the normal interstellar grains is much lower than graphite.”