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.
Planet Overview - Earth. Earth is the only planet we know of in our solar system that humans can live on. No other planet has oceans, other life forms, and enough oxygen to comfortably breathe. Because we have so much water, Earth is called the Blue Planet. From space the oceans combined with the atmosphere makes the planet look blue. Earth - What It's All About. About 71 per cent of the Earth is covered with water. Earth is the only planet where water can exist in liquid form on the surface.