( Pluto ( ( ( rotates ( once ( on ( its axis ) ) ) ) ( every ( 6.39 ( Earth days ) ) ) ) ; ) )
(ROOT (S (NP (NNP Pluto)) (VP (VBZ rotates) (ADVP (RB once) (PP (IN on) (NP (PRP$ its) (NNS axis)))) (NP (DT every) (CD 6.39) (NNP Earth) (NNS days))) (: ;)))
Pluto rotates once on its axis every 6.39 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))))) (. .)))