So I was sitting on the patio looking at the now-waning Harvest Moon, and I remembered a bit from the original Cosmos TV series about the monks who witnessed a small asteroid impact on the Moon in mumblemumbleyearsomething and I wondered; how big of an asteroid would have to hit the Moon in order to eject enough (or large enough) debris in order to pose a threat of ground impacts on the Earth?
I assume the biggest factor would be generating enough velocity for the debris to escape the Moon’s gravity well, and then the debris being large enough to survive atmospheric re-entry, etc. I also suppose that the debris pattern would be such that we would experience multiple events (similar to standard meteor showers from comets) as the Earth moved through the debris cloud, but on a much shorter timescale. Maybe twice a month? Until the debris was swept clean of local space around Earth.
Anyway, just a thought, and I know we have some pretty sharp tacks when it comes to astronomy/astrophysics/etc. around here, so I thought I’d throw it out for discussion.