It seems unlikely to me that those would kill all of the earthbound population while still leaving the earth habitable enough for our returning astronauts. (If they kill, say, 99.99% of the population then the survivors will far outnumber the astronauts.)
It seems unlikely to me that those would kill all of the earthbound population while still leaving the earth habitable enough for our returning astronauts. (If they kill, say, 99.99% of the population then the survivors will far outnumber the astronauts.)