Sentence:  No attempts to measure the radio emission of the remaining planets have been reported , and , because of their distances , small <WSD>diameters</WSD> , or low temperatures , the thermal radiation at radio wave lengths reaching the earth from these sources is expected to be of very low intensity . 
Meaning of the word marked with <WSD> tags:  the length of a straight line passing through the center of a circle and connecting two points on the circumference