text: In 1906 , Percival Lowell , a wealthy Bostonian who had founded the Lowell Observatory in Flagstaff , Arizona in 1894 , started an extensive project in search of a possible ninth planet , which he termed `` Planet X '' .
simplified: In 1906 , Percival Lowell , a person from Boston began an extensive to search the ninth planet . He called it `` Planet X '' .