Our astronaut in space would experience something quite different from one on Mars, where sound could be heard with a modest microphone and some technological help. The Martian atmosphere is less than 1 percent as dense as Earth at sea level. This probably is not enough to carry sounds that the human ear could detect, experts say. Of course, anyone outside on Mars would be wearing a pressurized suit, so the only sounds they’d hear would have to be electronically delivered. There’s no reason a sensitive external microphone could not be used to pick up sounds and amplify them to some terrestrial approximation.