^* You often read that astronauts’ skulls get thicker in zero G. I assumed that this was because the extra fluid in the top half of the body plumps the brain, and that the body responds to the increased pressure by thickening the cranium—just as it responds to increased blood pressure by thickening the arteries. “Interesting hypothesis,” said NASA physiologist John Charles. Then he told me it’s not true that living in space makes astronauts’ skulls thicker. Or not literally anyway. Charles says they do routinely develop the “space stupids”—cognitive impairment brought on by “sleep deprivation, over-scheduled time-lines, and all the other indignities we heap onto astronauts.”