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.
Since there is no support for the contention that life exists elsewhere, much attention has been diverted to searching for planetary conditions favorable for life. Mars has been the focus of this attention for a very long time. Mars is about half the size of the earth, and it has at least a thin atmosphere.