Pluto and Right-Wrong Math
February 18, 1930
1930 1930

NAT

NINTH PLANET, SOLAR SYSTEM
	After discovering Neptune through variations in the orbit of Uranus, Neptune's co-discoverer, Urbain Leverrier, said: "After 30 or 40 years of observing the new planet, we will be able to use it in turn for the discovery of the one that follows it in order of distance from the sun."
	And that is how it turned out -- sort of.
	In 1905, astronomer Percival Lowell began a serious search for a ninth planet, which he dubbed "Planet X." Until his death in 1916 he and the staff at Lowell Observatory searched for this "trans Neptunian" planet. They made repeated calculations and numerous sky surveys -- all in vain. Thomas Gill even photographed the faint planet in 1915, but it was hidden among more than 1,200 other objects. Planet X went unnoticed.
	Then, in 1929, Clyde Tombaugh, a 22-year-old amateur astronomer, was invited to be an assistant at the observatory. On April 6, 1929 he began a painstaking search for Planet X. For 10 months, he examined photographs of millions of stellar objects, often for three to six hours at a time. Then, on Feb. 18, 1930, Tombaugh found an object that had moved across the starry background. After checking earlier photographs of the same region for confirmation, he announced his discovery to his colleagues. The planet was near where Percival Lowell predicted in 1915.
	The Lowell Observatory called the planet "Pluto," so its symbol became PL, which conveniently honored Percival Lowell (P.L.).
	However, further study shows that Pluto is too small to cause the variations in Uranus' and Neptune's orbits. Lowell's calculations were wrong. Thus, Tombaugh and others were looking in about the right place, but for the wrong reason. It wasn't Lowell's calculations that found Pluto, but his faith, and Clyde Tombaugh's dogged persistence.
	In 1978, James Christy of the U.S. Naval Observatory, examined a photograph of Pluto that was marked "POOR" because of a streak on Pluto's side. But he noticed other photos of Pluto also had bulgy streaks. In fact, the bulge appeared on both sides of Pluto. These weren't POOR photos; the streaks showed a moon! Christy named it Charon after the boatman who ferried the dead to the realm of the god Pluto. It was also no coincidence that his wife's nickname was Char (Charlene).
	Pluto was not visited by the Voyager spacecraft, so we still know little about it -- but we still have a chance. On Sept. 12, 1989, Pluto came within 2.75 billion miles of the sun, the closest approach in its orbit. But by 1999 it will again replace Neptune as the most distant planet in the solar system. Pluto takes 248 years to orbit the sun, so if we don't send a Voyager-like craft to visit it soon, we will have to wait several more generations for another opportunity.