( It ( ( ( rotates ( on ( its axis ) ) ) ( once ( every ( 60 ( Earth days ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ rotates) (PP (IN on) (NP (PRP$ its) (NNS axis))) (PP (RB once) (NP (DT every) (CD 60) (NNP Earth) (NNS days)))) (. .)))
It rotates on its axis once every 60 Earth days.
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (PP (IN on) (NP (PRP$ its) (NNS axis)) (ADVP (RB once))) (CC times) (PP (IN in) (NP (CD one) (NN day))))) (. .)))