The atmosphere pushes down on the water molecules. This stops them from escaping gravity. When you have no atmosphere then you have no pushing on the water molecules. This means the water molecules will just evaporate. read more
The boiling point temperature or water decreases as the amount of vacuum increases. At near perfect vacuum of 29.9199 inches of HG vacuum, the boiling point of water is approximately -90°F or - 68°C. read more
Normally, boiling water cannot cook food to more than 212 degrees Fahrenheit, as that is the boiling point of water under one atmosphere. By raising the pressure inside the vessel, however, a pressure cooker increases that temperature, allowing food to cook much faster. read more
A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100 °C (212 °F) at sea level, but at 93.4 °C (200.1 °F) at 2,000 metres (6,600 ft) altitude. read more