Sentence:  No attempts to measure the radio emission of the remaining planets have been reported , and , because of their distances , small diameters , or low temperatures , the thermal radiation at radio <WSD>wave</WSD> lengths reaching the earth from these sources is expected to be of very low intensity . 
Meaning of the word marked with <WSD> tags:  the distance (measured in the direction of propagation) between two points in the same phase in consecutive cycles of a wave