sentences:  Water on Mars exists today almost exclusively as ice, with a small amount present in the atmosphere as vapour.Some liquid water may occur transiently on the Martian surface today but only under certain conditions.No large standing bodies of liquid water exist because the atmospheric pressure at the surface averages just 600 pascals (0.087 psi)—about 0.6% of Earth's mean sea level pressure—and because the global average temperature is far too low (210 K (−63 °C)), leading to either rapid evaporation or freezing.