Background
Clyde Tombaugh discovered Pluto at Lowell Observatory on February 18, 1930, and later worked in New Mexico at White Sands before joining New Mexico State University in Las Cruces.12 NMSU archival records document his long professional career, including correspondence and observational work spanning Lowell, White Sands, and NMSU.23
Origin of the UFO Claim
In a signed first-person statement titled "An Unusual Aerial Phenomenon" dated August 7, 1957, Tombaugh wrote that he saw a geometric group of faint bluish-green rectangular lights from his Las Cruces backyard in August 1949.4 He stated that his wife and mother-in-law also saw the lights, which moved south-southeasterly, appeared to foreshorten, and faded from view near 35 degrees above the horizon after about three seconds with no sound.4 NICAP's case archive preserves this 1949 Las Cruces report and related source materials connected to Tombaugh's account.5
What Tombaugh Documented
Tombaugh wrote that he had spent thousands of hours watching the night sky and had never seen anything similar before that event.4 Surviving archival reproductions include sketches attributed to his wife and later comparative renderings that show how witnesses and later writers represented the rectangular-light formation.67
How the Account Evolved
A 1951 U.S. Air Force Project Twinkle report included a secondhand statement that Tombaugh had not observed an unexplainable aerial object despite extensive sky-watching, showing that official-era summaries did not present a single consistent narrative.8 In the July 29, 1968 House UFO symposium record, James E. McDonald described the Las Cruces case in detail, noted discussions with Tombaugh, and repeated Tombaugh's remark that he had not seen anything like it before or since.9 By the late 1960s, Tombaugh's sighting was used as a central example in debates between atmospheric-explanation arguments and claims that some reports remained unresolved.89