In looking for other planets that might have life, astronomers focus especially on finding planets that

are the same size as earth
have rocky surfaces
have liquid water
have nitrogen-filled atmospheres

have liquid water

Explanation:

Liquid water and atmosphere are important for life to exist on a planet. Life can exist in the form of unicellular. It must not be multi-cellular organisms like animals.  A cell is majorly composed of water. Thus, liquid water is very essential for life to exist. All the life processes require liquid water. Thus, astronomers focus especially on finding planets that have liquid water.

igneous rocks also form where plates converge. the subducting plate melts as it sinks into the crust of the earth, and the melt rises into the overriding plate forming volcanoes. metamorphic rocks are formed mainly in the lithosphere, wherever there is high pressure and high temperature. -woods