You’d also have a hard time talking on Mars, he says. Putting aside the health hazards of taking off your space helmet, Martian air just doesn’t carry the human voice as well as terrestrial air does. While our atmosphere is made up mostly of nitrogen, air on Mars is almost entirely carbon dioxide. The size and shape of the CO2 molecule make it prone to spinning when hit by vibrations of the type human vocal cords produce, and that rotation leeches energy from sound waves, making them die out quickly. On the bright side, one thing future outposts won’t have to worry about will be noise complaints.