Ink signature, "Clyde W. Tombaugh, Discovered 9th planet, Pluto, on 18 Feb. 1930,” on an off-white 5 x 3 card, the reverse of which bears an ALS in pencil by Tombaugh signed with his initials, “CWT.” Dated June 23, 1996, the brief handwritten letter reads: "I get hundreds of requests for autographed photos. I cannot cope with this problem too much time and expense." In very fine condition. Encapsulated and graded by PSA/DNA as "MINT 9."