( Mercury ( ( is ( ( the planet ) ( that ( is ( closest ( to ( the Sun ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Mercury)) (VP (VBZ is) (NP (NP (DT the) (NN planet)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (ADJP (ADJP (JJS closest)) (PP (TO to) (NP (DT the) (NNP Sun))))))))) (. .)))
Mercury is the planet that is closest to the Sun.
(ROOT (S (NP (NNP Mercury)) (VP (VBZ is) (ADJP (ADJP (JJS closest)) (PP (TO to) (NP (PRP$ our) (NN sun))))) (. .)))