( ( Professor Kirkwood ) ( correctly ( ( ( ( explained ( this occurrence ) ) ( as ( ( an effect ) ( of ( ( Jupiter 's ) gravity ) ) ) ) ) ( on ( the asteroids ) ) ) . ) ) )
(ROOT (S (NP (NNP Professor) (NNP Kirkwood)) (ADVP (RB correctly)) (VP (VBD explained) (NP (DT this) (NN occurrence)) (PP (IN as) (NP (NP (DT an) (NN effect)) (PP (IN of) (NP (NP (NNP Jupiter) (POS 's)) (NN gravity))))) (PP (IN on) (NP (DT the) (NNS asteroids)))) (. .)))
Professor Kirkwood correctly explained this occurrence as an effect of Jupiter's gravity on the asteroids.
(ROOT (S (NP (NNP High) (NNP gravity)) (VP (VBZ explains) (NP (NP (DT the) (JJ spherical) (NN shape)) (PP (IN of) (NP (NNS ceres)))) (, ,) (SBAR (IN once) (S (VP (VBD thought) (S (VP (TO to) (VP (VB be) (NP (DT the) (JJS largest) (NN asteroid))))))))) (. .)))