The impeller made out of cast material in many cases may be called rotor, also. It is cheaper to cast the radial impeller right in the support it is fitted on, which is put in motion by the gearbox from an electric motor, combustion engine or by steam driven turbine.
Earth remains the only known planet to host life, due to a unique combination of factors. However, continued monitoring of alien worlds might one day change that, by finding other planets that share these attributes or by discovering other ways that life has found to blossom in the universe.
Europa is generally considered the most likely extraterrestrial world in our Solar System to harbor life. Jupiter's fourth largest moon could contain more water than all of Earth's oceans combined, and where there is water, there could be life. Europa's surface ice is estimated to be roughly 10 miles thick, meaning any life in the oceans below would have to rely on a source of energy other than photosynthesis.