Water can exist as solid, liquid or gas on Earth and other planets. When water exists as a solid it is called ice; as a liquid it is called water and as a gas it is called water vapor. The state that the water exists depends on the temperature of the planet. In areas where the temperature is below 0 degrees Celsius, water would exist as a solid. Between 0 degrees and 100 degrees Celsius water will exist as a liquid. Water vapor is formed at temperatures higher than 100 degrees Celsius. Water vapor, however, can exist at temperatures below 100 degrees Celsius. This occurs when water evaporates. In this case, water molecules move out of the liquid state into the gaseous state due to their energy.