  The unique biosignature of life on Earth is the homochirality of organic
compounds such as amino acids, proteins, and sugars. The origin of this
homochirality has remained a mystery for over a century. While high-energy
spin-polarized (spin-up or spin-down) electrons (SPEs) from the $\beta$ decay
of radioactive nuclei discovered by Lee and Yang (1956) and Wu et al. (1957)
have been proposed as a potential source of symmetry breaking, their exact role
on homochirality is much debated. Here we suggest magnetically aligned dust
grains as a new source of SPEs due to photoemission of electrons having aligned
spins by the Barnett effect. For the interstellar UV radiation field of
strength $G_{\rm UV}$, we found that the SPE emission rate is $\Gamma_{\rm
pe}^{\rm SPE}\sim 10^{-14}G_{\rm UV}$ electrons per second per H, the fraction
of spin-polarized to total photoelectrons is $\sim 10\%$, and the SPE yield
(photoelectron number per UV photon) can reach $\sim 1\%$, using the modern
theory of grain alignment. Low-energy SPEs from aligned grains would cause
chiral symmetry breaking of interstellar chiral molecules due to spin-selective
(dipole-dipole) interactions. Finally, we suggest magnetically aligned grains
as chiral agents that facilitate and enrich the chiral asymmetry of chiral
molecules. Our proposed mechanism might explain the detection of chiral
asymmetry in the ISM, comets, and meteorites due to the ubiquitous UV radiation
and magnetically aligned grains, paving the way for understanding the origin
and distribution of life in the universe. This mechanism based on magnetic
grain alignment implies the role of magnetic fields on chirality symmetry
breaking.
