For this reason , the search for Planet X again started in 1929 . The director of the mission , Vesto Melvin Slipher , gave the job to Clyde Tombaugh , a 23-year-old Kansas man . Due to a ten-year legal battle with Constance Lowell , Percival 's widow , who attempted to wrest the observatory 's million-dollar portion of his legacy for herself , the search for Planet X did not resume until 1929 , when its director , Vesto Melvin Slipher , summarily handed the job of locating Planet X to Clyde Tombaugh , a 23-year-old Kansas man who had just arrived at the Lowell Observatory after Slipher had been impressed by a sample of his astronomical drawings .