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.
Earth is the only place that we know for certain supports life. Many claims have been made by observers who thought they saw evidence of life on Mars, but we now know they were tricked by the very difficult measurements.