Tombaugh was born in Streator, LaSalle County, Illinois. After his family moved to Burdett, Kansas, Tombaugh built his first telescope and sent drawings of his observations of Jupiter and Mars to the Lowell Observatory. These resulted in a job offer. Tombaugh was employed at the Lowell Observatory from 1929 to 1945. Following his discovery of Pluto, Tombaugh earned astronomy degrees from the University of Kansas and Northern Arizona University. He taught astronomy at New Mexico State University from 1955 until his retirement in 1973. He died in Las Cruces, New Mexico, 1997 and was survived by his wife Patricia, daughter Annette and son Alden, a retired banker. Tombaugh was an active Unitarian-Universalist.
The asteroid 1604 Tombaugh, discovered in 1931, is named after him. He himself discovered 14 asteroids, beginning with 2839 Annette in 1929, mostly as a by-product of his search for Pluto and his further searches for other celestial objects. Tombaugh named some of them after his wife, children and grandchildren. The Royal Astronomical Society awarded him the Jackson-Gwilt Medal in 1931. Some of his ashes are being carried on the New Horizons spacecraft which is traveling towards Pluto.
Discovery of Pluto
While a young researcher working for the Lowell Observatory in Flagstaff, Arizona, Tombaugh was given the job to perform a systematic search for a trans-Neptunian planet (also called Planet X), which had been predicted by Percival Lowell and William Pickering.
Tombaugh used the observatory's 13-inch astrograph to take photographs of the same section of sky several nights apart. He then used a blink comparator to compare the different images. When he shifted between the two images, a moving object, such as a planet, would appear to jump from one position to another, while the more distant objects such as stars would appear stationary. Tombaugh noticed such a moving object in his search, and subsequent observations showed it to be the object we call Pluto. The discovery was made on Tuesday, February 18, 1930, using images taken in January of the same year.
The name "Pluto" was suggested by Venetia Burney: an 11-year-old English school girl who is still alive and living in England. It won out over numerous other suggestions partly because it was named after the Roman god of the underworld (who was able to render himself invisible) and because Percival Lowell's initials PL formed the first 2 letters. The name Pluto was officially adopted on 1 May 1930.
On August 24, 2006, the International Astronomical Union moved Pluto from the eight "classical planets" and grouped it in with two similarly sized "dwarf planets." Tombaugh's widow Patricia stated after the IAU's decision that while Clyde may have been disappointed with the change since he had resisted attempts to remove Pluto's planetary status in his lifetime, he would have accepted the decision now if he were alive. She notes that Clyde "was a scientist. He would understand they had a real problem when they start finding several of these things flying around the place."
Tombaugh continued searching for some years after the discovery of Pluto, and the lack of further discoveries left him satisfied that no other object of a comparable magnitude existed near the ecliptic. No more Trans-Neptunian objects were discovered until (15760) 1992 QB1, in 1992.
However, more recently the relatively bright object (136472) 2005 FY9 has been discovered. It has a relatively high orbital inclination, but at the time of Tombaugh's discovery of Pluto, 2005 FY9 was only a few degrees from the ecliptic near the border of Taurus and Auriga. Unfortunately, this position was also very near the galactic equator, making it almost impossible to find such an object within the dense concentration of background stars of the Milky Way.
Tombaugh discovered a total of 14 asteroids, during his search for Pluto and years of follow-up searches looking for another candidate for the postulated Planet X.
Interest in UFOs
Tombaugh was probably the most eminent astronomer to have reported seeing Unidentified Flying Objects and to support the Extraterrestrial hypothesis. On August 20, 1949, Tombaugh saw several UFOs near Las Cruces, New Mexico. He described them as six to eight rectangular lights, stating:
"I doubt that the phenomenon was any terrestrial reflection, because... nothing of the kind has ever appeared before or since... I was so unprepared for such a strange sight that I was really petrified with astonishment."
A similar shocked response has been reported by many other who claim to have seen mysterious aerial objects.
Another sighting by Tombaugh a year or two later while at a White Sands observatory was of an object of -6 magnitude, four times brighter than Venus at its brightest, going from the zenith to the southern horizon in about 3 seconds. The object executed the same maneuvers as in Tombaugh's first sighting.
Tombaugh was also later to report having seen three of the mysterious green fireballs, which suddenly appeared over New Mexico in late 1948 and continued at least through the early 1950s. Despite this, the final report of Project Twinkle claimed that he "... never observed an unexplainable aerial object despite his continuous and extensive observations of the sky." In 1956 Tombaugh had the following to say about his various sightings:
"I have seen three objects in the last seven years which defied any explanation of known phenomenon, such as Venus, atmospheric optic, meteors or planes. I am a professional, highly skilled, professional astronomer. In addition I have seen three green fireballs which were unusual in behavior from normal green fireballs ... I think that several reputable scientists are being unscientific in refusing to entertain the possibility of extraterrestrial origin and nature."
Shortly after this in January 1957, in an Associated Press article in the Alamogordo Daily News titled "Celestial Visitor's May Be Invading Earth's Atmosphere," Tombaugh was again quoted on his sightings and opinion about them.
"Although our own solar system is believed to support no other life than on Earth, other stars in the galaxy may have hundreds of thousands of habitable worlds. Races on these worlds may have been able to utilize the tremendous amounts of power required to bridge the space between the stars..."
Tombaugh said he has observed celestial phenomena which he could not explain, but has seen none personally since 1951 or 1952. "These things, which do appear to be directed, are unlike any other phenomena I ever observed. Their apparent lack of obedience to the ordinary laws of celestial motion gives credence."
In 1949, Tombaugh had also told the Naval missile director at White Sands Missile Range, Commander Robert McLaughlin, that he had seen a bright flash on Mars in August 1941, which he now attributed to an atomic blast. Tombaugh also noted that the first atomic bomb tested in New Mexico would have lit up the dark side of the Earth like a neon sign and that Mars was coincidentally quite close at the time, the implication apparently being that the atomic test would have been visible from Mars.
In June 1952, Dr. J. Allen Hynek, an astronomer acting as a scientific consultant to the Air Force's Project Blue Book UFO study, secretly conducted a survey of fellow astronomers on UFO sightings and attitudes while attending an astronomy convention. Tombaugh and four other astronomers told Hynek about their sightings, including Dr. Lincoln La Paz of the University of New Mexico. Tombaugh also told Hynek that his telescopes were at the Air Force's disposal for taking photos of UFOs, if he was properly alerted.
Near-Earth satellite search
Tombaugh's offer may have led to his involvement in a search for near-Earth satellites, first announced in late 1953 and sponsored by the Army Office of Ordnance Research. Another public statement was made on the search in March 1954, emphasizing the rationale that such an orbiting object would serve as a natural space station. However, according to Donald Keyhoe, later director of the National Investigations Committee on Aerial Phenomena (NICAP), the real reason for the sudden search was because two near-Earth orbiting objects had been picked up on new long-range radar in the summer of 1953, according to his Pentagon source.
By May 1954, Keyhoe was making public statements that his sources told him the search had indeed been successful, and either one or two objects had been found. However, the story didn't really break until August 23, 1954, when Aviation Week magazine stated that two satellites had been found only 400 and 600 miles out. They were termed "natural satellites" and implied that they had been recently captured, despite this being a virtual impossibility. The next day, the story was in many major newspapers. Dr. La Paz was implicated in the discovery in addition to Tombaugh. La Paz had earlier conducted secret investigations on behalf of the Air Force on the green fireballs and other unidentified aerial phenomena over New Mexico.
La Paz vehemently denied his involvement in the search, although the New York Times reported on August 29 that a source close to the project said that the story was true and La Paz was indeed involved, in fact had been the one to spot and identify the objects as natural rather than artificial satellites. The same source denied the search had anything to do with flying saucers.
However, both La Paz and Tombaugh were to issue public denials that anything had been found. The October 1955 issue of Popular Mechanics magazine reported:
"Professor Tombaugh is closemouthed about his results. He won't say whether or not any small natural satellites have been discovered. He does say, however, that newspaper reports of 18 months ago announcing the discovery of natural satellites at 400 and 600 miles out are not correct. He adds that there is no connection between the search program and the reports of so-called flying saucers."
At a meteor conference in Los Angeles in 1957, Tombaugh reiterated that his four year search for "natural satellites" had been unsuccessful. In 1959, Tombaugh was to issue a final report stating that nothing had been found in his search.
In popular culture
In Robert A. Heinlein's 1958 science fiction novel, Have Space Suit—Will Travel, there is a moon base called Tombaugh Station. And, "Professor Tombaugh (the one the station was named for) was working on a giant electronic telescope to photograph" Pluto.
Wilson Tucker published the 1960 novel To the Tombaugh Station (Ace Double).
The 2006 album The Avalanche by Sufjan Stevens includes a song titled "For Clyde Tombaugh".
In the Star Trek Universe there is a Federation starship USS Tombaugh, named after the astronomer. It was mentioned in the Star Trek: Voyager episode "Infinite Regress".
In the computer game Descent: Freespace, there is a Terran station in the Ribos system named after Tombaugh which is obliterated by the Shivan destroyer, Lucifer.