( ( As ( they ( near ( the sun ) ) ) ) ( , ( ( ( the ( sun 's ) ) heat ) ( ( ( ( sublimates ( ( the ( comet 's ) ) ices ) ) and ) ( releases ( ( dust particles ) ( which ( produces ( ( the ( comet 's ) ) tail ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (NP (PRP they)) (PP (IN near) (NP (DT the) (NN sun))))) (, ,) (NP (NP (DT the) (NN sun) (POS 's)) (NN heat)) (VP (VP (VBZ sublimates) (NP (NP (DT the) (NN comet) (POS 's)) (NNS ices))) (CC and) (VP (VBZ releases) (NP (NP (NN dust) (NNS particles)) (SBAR (WHNP (WDT which)) (S (VP (VBZ produces) (NP (NP (DT the) (NN comet) (POS 's)) (NN tail)))))))) (. .)))
As they near the sun, the sun's heat sublimates the comet's ices and releases dust particles which produces the comet's tail.
(ROOT (S (NP (JJ Comet) (NNS tails)) (VP (ADVP (RB always)) (VBP point) (PRT (RP away)) (PP (IN from) (NP (NP (DT the) (NN sun)) (PP (RB instead) (IN of) (S (VP (VBG trailing) (PP (IN behind) (NP (DT the) (ADJP (JJ comet) (PP (IN because) (NP (NN dust) (NNS particles)))) (NN recoil))))))))) (. .)))