Home Lesson 1 Science Notes Lesson 2. Science Notes Lesson 2. . So far as we know, life needs a liquid of some kind in order to work chemically. The life forms that we are familiar with use water.
Water is made of simple atoms and is plentiful in the universe.
Perhaps there are life forms that use other liquids, such as liquid methane, but we don't know about them. We tend to think in terms of water-based life. It seems reasonable to believe that planets that are close to the sun are too hot to have liquid water on their surfaces. Planets that are far away would probably be too cold. There is a region in the middle where planets might have temperatures that would permit liquid water to exist on their surfaces.