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.
Venus is too hot, Mars is too cold. Earth is just right. Noted astronomer Carl Sagan described Earth as seen from distant space as a pale blue dot, signaling our planet as an outpost of life. It's because of the hydrosphere that life flourishes on Earth. Just as important as the existence of water is the hydrologic cycle that moves water around the globe. Driven by solar energy, surface waters evaporate into the atmosphere, condense, and fall back to the surface as precipitation, shaping continents, creating rivers, and filling lakes.