Sadly, Lowell was to die, at the age of 61, before he could conclusively identify Planet X. In fact, though, in 1915 his observatory had captured two indistinct images of what would later be called Pluto. However, at the time nobody recognized them for what they were.
After Lowell’s death, there was an unfortunate pause in the search for this Planet X. This was caused by a legal dispute between Lowell’s widow, Constance, and the observatory’s management. Happily, though, the search recommenced in 1929 under the guidance of the observatory’s director, Vesto Slipher.
Slipher entrusted the search for Planet X to Clyde Tombaugh, who was then just 23 years of age. Slipher had offered Tombaugh a job after he’d sent some illustrations of Jupiter and Mars to the observatory. And as it turned out, it was to be an inspired appointment.