The Ex-Farm Boy Who Found Pluto : Retired Astronomer Recalls His 1930 Discovery of Ninth Planet
Leave it to a farm boy to find a needle in a haystack.
In this case, it was 22-year-old Clyde Tombaugh, who rose to the astronomical task of finding a planet, Pluto, among the millions of stars. The year was 1930.
“There were 400,000 star images per (photographic) plate, and I photographed 70% of the sky, so I figure I looked at about 90 million stars,” Tombaugh said. “When people ask if I think I’ve missed another planet, I say, ‘No, I don’t think so, but you are welcome to examine my plates.’ ”
Tombaugh shared his memories of that discovery of more than five decades ago with a sold-out lecture audience at Griffith Observatory Friday night. The 81-year-old New Mexico State University professor emeritus spryly climbed the observatory steps before the lecture to be photographed looking through the telescope.
Now that his planet-hunting and teaching days are over, he enjoys autographing copies of his book, “Out of the Darkness,” and retelling his story that stretches from the Midwest to the edges of the solar system.
Tombaugh was born and reared on a farm near Streator, Ill., and when he was 16 moved to another outside Burdett, Kan., where he finished high school. Geography was his favorite subject, “until I found the telescope.”
Using models he built in his backyard--one a nine-inch telescope fashioned out of a cream separator, a shaft from his father’s 1910 Buick, a spring from the seat of a mowing machine and another part from a straw spreader--he studied Mars and Jupiter. In 1928, the amateur astronomer sent the drawings he made of those planets to the experts at Lowell Observatory for comment. They responded by offering him a job.
Percival Lowell, founder of the Flagstaff, Ariz., observatory, had predicted the existence of a planet--a heavenly body that shines by reflected sunlight and revolves about the sun--beyond Neptune, but died in 1916 before his “Planet X” was discovered. He theorized that a sufficient mass was responsible for the irregularities in Uranus’ and Neptune’s orbits. The financially strapped observatory was looking to boost its reputation, Tombaugh said, and wanted to make a discovery through photographs made with its 13-inch wide-angled telescope.
“They didn’t want to pay a high salary, and I fit the bill.”
Tombaugh spent many cold nights in the unheated observatory--"Heat would interfere with light from the stars"--photographing sections of the sky and his days examining, or “blinking,” the photo plates. Using side-by-side plates taken several days apart of the same section of sky, he would compare the 400,000 black specks on each white plate. The stars would appear in the same position, but two dots that didn’t match would indicate a moving object.
“I will say that I did get a little tired of it toward the last,” he said.
Within a year of his arrival at Lowell Observatory, Tombaugh became one of the superstars of astronomy; more people have walked on the moon than discovered planets. Mercury, Venus, Mars, Jupiter and Saturn can be seen with the naked eye. Sir William Herschel of Britain located Uranus in 1781. Neptune was discovered by German and French astronomers Johann Galle and Urbain le Verrier in 1846.
And then came Tombaugh’s discovery of Pluto on Feb. 18, 1930.
“It was about 4 o’clock in the afternoon, and I had been blinking these two plates for quite some time. And while I did this, the machine made a clicking noise that could be heard down across the hall by Dr. (C. O.) Lampland, a colleague of mine. Well, he told me later that he knew something was up because the clicking had stopped.”
An Eighth-Inch Shift
The quiet persisted for about 45 minutes as Tombaugh rechecked plates he had made Jan. 23 and 29. One dot among the thousands had shifted about an eighth of an inch over those six days as the Earth had traveled 600,000 miles: Pluto.
He told fellow astronomer Lampland the news and raced to the office of observatory director V. M. Slipher, and the plates underwent further examination. Slipher told the two not to mention their finding until a formal announcement could be made later.
“They wanted to brace themselves for the big storm that would occur once it was announced,” Tombaugh said.
Clouds prevented an anxious Tombaugh from making another plate early that next night.
“I was a bachelor in those days, so I went into town for something to eat. Then I went to a movie, ‘The Virginian’ with Gary Cooper, and when I came out it was still cloudy so I went back to the observatory and went to bed.”
The following night’s sky cooperated, he said, and another plate of the planet’s trek was recorded.
The world learned of Pluto on March 13, 1930, the anniversary of Lowell’s birth date.
And in the publicity that followed, Patsy Edson found her husband-to-be as he began his quest for a college degree.
“I saw his picture in the Kansas City Star,” she said, “and my brother, who was going to the University of Kansas, said, ‘You are going to meet that man. He’s in one of my classes.’ ” Today the Las Cruces, N.M., couple are great-grandparents.
Picking a name for the planet was no easy task either, Tombaugh said.
“I’d like to say we called it Pluto because it was so doggone hard to find,” he said, breaking up the audience. Far from any association with the Disney cartoon character, the planet was named for the ruler of the underworld.
“We had quite a time looking for a name, because most of the good names of mythology had been given to the asteroids,” Tombaugh said. “And its moon is named Charon, who in mythology was the boatman who transported souls of the dead across the river Styx to Hades, which was Pluto’s realm.”
Outside the Zodiac
The ninth planet, Tombaugh said, “is a bit of an oddball because it is found outside the zodiac.” The plane of its orbit differs about 17 degrees from that of the other planets.
The oddities don’t end there.
With a diameter of about 1,500 miles, Pluto is by far the smallest planet, a little smaller than Earth’s moon. It makes one revolution of the sun in 248.4 years in an eccentric orbit that currently places it closer to the sun than the eighth planet, Neptune. Pluto will become the outermost planet again in March, 1999.
Charon, discovered in 1978, is about 40% of Pluto’s diameter and orbits the planet every 6.4 days, the same time that it takes Pluto to turn once on its axis. Therefore Charon hangs over one spot on Pluto’s surface.
Pluto is nine times as far from the sun as Earth is. Temperatures on the planet’s surface are estimated to be more than 400 degrees below zero Fahrenheit.
“It’s probably a methane snowball,” Tombaugh said. “And right now, while it’s closest to the sun, some of that is probably melting to form a methane atmosphere.”
The discovery of Pluto did not confirm Lowell’s theories about the gravitational disturbances in Uranus’ and Neptune’s motions. The mystery remains, as further research has shown that Pluto’s mass is too small to affect the other two planets’ motions.
There may be another planet in our own solar system beyond Pluto, Tombaugh said, “but it would be very faint and it would take a massive effort to find it.”
And planets, maybe some with life, in other solar systems?
Tombaugh made the odds pretty good that there is life out among the stars: “If you take all the grains of sand on all the world’s beaches--hundreds of thousands of miles--there would still be 100 stars for every grain of sand.”