Audio Guide：

Liquid water is a necessary condition for the formation of life. Therefore, to search for extraterrestrial life, we must first find places where liquid water can exist, which form the so-called “habitable zone.” However, water freezes when the temperature is too low and evaporates when the temperature is too high. Therefore, the “habitable zone” can only be found around stars where temperature is suitable. At the moment, Earth and Mars are in the habitable zone of the solar system; however, the range of the habitable zone changes as the Sun evolves. The habitable zone only takes up a very small percentage in this vast universe; and the solar system is also within the habitable zone of the galaxy.