( ( Back ( to ( the ( Index Saturn ) ) ) ) ( ( ( Saturn 's ) atmosphere ) ( ( ( is ( almost entirely ) ) ( ( hydrogen and ) helium ) ) . ) ) )
(ROOT (S (ADVP (RB Back) (PP (TO to) (NP (DT the) (NNP Index) (NNP Saturn)))) (NP (NP (NNP Saturn) (POS 's)) (NN atmosphere)) (VP (VBZ is) (ADVP (RB almost) (RB entirely)) (NP (NP (NN hydrogen)) (CC and) (NP (NNP helium)))) (. .)))
Back to the Index Saturn Saturn's atmosphere is almost entirely hydrogen and helium.
(ROOT (S (NP (NNP Saturn)) (VP (VBZ is) (VP (VBN made) (ADVP (RB mostly)) (PP (IN of) (NP (NN helium) (CC and) (NN hydrogen))))) (. .)))