By the time the alarms go off, he’s back on his feet, hoping the rover wasn’t filming, but knowing that it was—that his face-first sprawl on the surface of Phobos has been recorded for posterity. The visor’s fiber-optic display flashes ominously: suit breach. His body, or some small sliver of it, has been exposed to the raw, airless vacuum of a Martian moon.

An astronaut can die many ways, but decompression is one of the more gruesome. A punctured space suit means a race to sanctuary, before the envelope of pure oxygen surrounding the body bleeds away and hypoxia causes the person to black out. Rapid pressure loss isn’t explosive, but it’s ugly: Water in the body begins to vaporize and tries to escape, the lungs collapse, and circulation shuts down.