Mars has such low atmospheric pressure that any water at the surface would boil away. In this activity, students see that they can get water to boil below its "typical" boiling temperature when they drop the pressure in a closed container. By extrapolating the pattern between boiling temperature and pressure, they realize that even water near its freezing point has enough kinetic energy to boil if the pressure is low enough. This activity is part of a larger set of activities called, "Is There Water on Mars".