 What likely caused the most problems?
F. No permanent installation with a human crew could survive at either extreme. The Major was counting on Sanderson knowing something about Mercury as well as the Sun when we camped at the Lab to make final preparations. But the only way to avoid it is to travel over the Pole, which would lose us days and offer us no guarantee of less activity to the west. There was an atmosphere and a constant atmospheric flow from Brightside to Darkside. Not much—the lighter gases had reached escape velocity and disappeared from Brightside millennia ago—but there was CO 2 , and nitrogen, and traces of other heavier gases. The trick was to find a passage that avoided those upheavals as far as possible.
 the high temperatures
 the toxic gases  the high temperatures  vehicle trouble  incorrect mapping