( ( Next ( to Earth ) ) ( , ( Mercury ( ( ( is ( the ( second ( most ( dense planet ) ) ) ) ) ( in ( our ( Solar System ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (JJ Next) (PP (TO to) (NP (NNP Earth)))) (, ,) (NP (NNP Mercury)) (VP (VBZ is) (NP (DT the) (JJ second) (RBS most) (JJ dense) (NN planet)) (PP (IN in) (NP (PRP$ our) (NNP Solar) (NNP System)))) (. .)))
Next to Earth, Mercury is the second most dense planet in our Solar System.
(ROOT (S (NP (NNP Mercury)) (VP (VBZ is) (NP (NP (DT the) (JJS smallest) (NN planet)) (PP (IN in) (NP (PRP$ our) (JJ solar) (NN system))))) (. .)))