  Many asteroids that make close encounters with terrestrial planets are in a
binary configuration. Here we calculate the relevant encounter timescales and
investigate the effects of encounters on a binary's mutual orbit. We use a
combination of analytical and numerical approaches with a wide range of initial
conditions. Our test cases include generic binaries with close, moderate, and
wide separations, as well as seven well-characterized near-Earth binaries. We
find that close approaches (<10 Earth radii) occur for almost all binaries on
1-10 million year timescales. At such distances, our results suggest
substantial modifications to a binary's semi-major axis, eccentricity, and
inclination, which we quantify. Encounters within 30 Earth radii typically
occur on sub-million year timescales and significantly affect the wider
binaries. Important processes in the lives of near-Earth binaries, such as
tidal and radiative evolution, can be altered or stopped by planetary
encounters.
