  The densest binary sphere packings have historically been very difficult to
determine. The only rigorously known packings in the alpha-x plane of sphere
radius ratio alpha and relative concentration x are at the Kepler limit alpha =
1, where packings are monodisperse. Utilizing an implementation of the
Torquato-Jiao sphere-packing algorithm [S. Torquato and Y. Jiao, Phys. Rev. E
82, 061302 (2010)], we present the most comprehensive determination to date of
the phase diagram in (alpha,x) for the densest binary sphere packings.
Unexpectedly, we find many distinct new densest packings.
