Sentence:  This result suggests a very high temperature at the solid surface of the planet , although there is the possibility that the observed radiation may be a combination of both thermal and non thermal components and that the observed spectrum <WSD>is</WSD> that of a black body merely by coincidence . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)