I’m basing this on astronomers using the same logic (published in Nature Astronomy and peer reviewed) to determine the probable density of unbound comets or asteroids in the galaxy and the conclusion that they are more common than originally thought. 

On Nov 6, 2018, at 1:05 PM, Rupert Boleyn <xxxxxx@gmail.com> wrote:

On 07Nov2018 0953, Sudnadja (via tml list) wrote:

Also, if it were a light sail, they must be incredibly common if we
just happened to see one in an automated survey shortly after that
survey started up. The galaxy would have had to have been flooded
with them.

That does not follow. The odds of us seeing one right after we start looking are very, very low if they aren't common, but very unlikely events can still occur. They just aren't the way to bet.