1930: Pluto Discovered, Controversy Ensues

High-resolution MVIC image of Pluto in enhanced color to bring out differences in surface composition. (Photo by NASA via Wikimedia Commons)

On this date in 1930, the dwarf planet Pluto was discovered.

Here are some things you may not have known about what was once considered the ninth planet in the solar system.

Although it wasn’t discovered until 1930, astronomers had predicted in the late 19th century that something besides the newly discovered Neptune was disturbing the orbit of the seventh planet, Uranus. Between 1909 and 1930, there were 16 prediscovery observations of Pluto in which the observer didn’t realize what was there.

Clyde Tombaugh, a 23-year-old astronomer was hired by the Lowell Observatory in Flagstaff, Arizona, to lead the effort to find what was called “Planet X.” He did this by comparing photographs of the night sky and looking for any undiscovered moving objects. On Feb. 18, 1930, Tombaugh discovered a moving object in pictures taken on January 23rd and 29th. Other photos confirmed the movement and the discovery was telegraphed to the Harvard Observatory on March 13.

The name Pluto was chosen from more than 1,000 suggestions. Pluto, after the mythological god of the underworld, was joined on the final short list of candidates by the names Minerva, after the goddess of wisdom, and Cronus, the son of Uranus and father of Zeus. The name Pluto was suggested by 11-year-old Venitia Burney, who had taken an interest in classical mythology.

After its discovery, Pluto was almost immediately seen as a disappointment. It was much smaller than it should have been. If it were the predicted Planet X, it should have been about seven times larger than Earth. In fact, at the time it was estimated to have a diameter of about 60 percent of that of the Earth. It also had an very elliptical orbit and was less reflective than anticipated. It was also determined that Pluto’s orbit takes it inside that of Neptune periodically. A stable orbital ratio means that the two bodies will never collide.

Almost immediately, Pluto’s status as a planet was called into question. The dimness and eccentric orbit were seen to be more like those of a comet or asteroid. A year later, other astronomers proposed that the new planet was not the cause of the orbital irregularities of Uranus, and that the discovery of Pluto was an accident.

Though the years, estimations of Pluto’s size were revised downward. In 1948, it was believed to be 1/10 the size of the Earth. In 1976, the estimate was down to 1/100th. The 1978 discovery of its moon, Charon, further lowered the estimate to about 1/500th. The most recent estimate puts Pluto at 1/459th the size of Earth.

In 1992, new information from Voyager 2’s flyby of Neptune allowed for more precise calculations of Neptune’s effect on the orbit of Uranus, eliminating the need for a Planet X to explain any irregularity.

In 2006, the International Astronomical Union created an official definition of the term “planet.” Pluto meets the first two conditions, which are orbiting the Sun and being massive enough to have its own gravity. It doesn’t meet the third condition of clearing its orbital neighborhood of other objects. Instead of being classified as the ninth planet, Pluto is considered the largest and second most massive dwarf planet in the solar system.

Our question: Which came first, the discovery of the dwarf planet Pluto, or the naming of Disney character Pluto?

Today is the anniversary of the election of Pope Francis, and it’s National Elephant Day in Thailand.

It’s unofficially National Workplace Napping Day, National Jewel Day, and National Open an Umbrella Indoors Day.

It’s the birthday of actor William H. Macy, who is 67; U2 bassist Adam Clayton, who is 57; and skier Mikaela Shiffrin, who is 22.

Because our topic happened before 1960, we’ll spin the wheel to pick a year at random.

This week in 1999, the top song in the U.S. was “Believe” by Cher.

The No. 1 movie was “Analyze This,” while the novel “The Testament” by John Grisham topped the New York Times Bestsellers list.

Weekly question: Pluto was originally the pet dog of which Disney character?

Submit your answer at triviapeople.com/test and we’ll add the name of the person with the first correct answer to our winner’s wall … at triviapeople.com. We’ll have the correct answer on Friday’s episode.



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