( This ( ( is ( particularly ( embarrassing ( for ( ( the asteroids ) ( whose ( orbits ( are ( ( Earth-crossing , ) ( which ( therefore ( ( could ( ( at ( some time ) ) ( in ( the future ) ) ) ) ( collide ( with ( our planet ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (ADJP (RB particularly) (JJ embarrassing) (PP (IN for) (NP (NP (DT the) (NNS asteroids)) (SBAR (WP$ whose) (S (NP (NNS orbits)) (VP (VBP are) (NP (NP (NNP Earth-crossing)) (, ,) (SBAR (WHNP (WDT which)) (S (ADVP (RB therefore)) (VP (MD could) (ADVP (IN at) (NP (DT some) (NN time)) (PP (IN in) (NP (DT the) (NN future)))) (VP (VB collide) (PP (IN with) (NP (PRP$ our) (NN planet))))))))))))))) (. .)))
This is particularly embarrassing for the asteroids whose orbits are Earth-crossing, which therefore could at some time in the future collide with our planet.
(ROOT (S (PP (IN In) (NP (DT the) (NN past))) (, ,) (NP (NP (NNS asteroids)) (VP (VBG colliding) (PP (IN with) (NP (NN planet) (NN earth))))) (VP (VBZ has) (VP (VBN caused) (NP (JJ many) (NNS organisms)) (S (VP (TO to) (VP (VB die) (PRT (RP off))))))) (. .)))