Pluto Under the Magnifying Glass: Who are you, Pluto?

By Leya Boic

Pluto (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

The discovery of Pluto

        To be a planet or not to be

                Pluto's first companion

                         The whole Pluto family

Introduction:

Everyone’s heard of Pluto, that little guy on the edge of our solar system. Not everyone knows how it was discovered, or what is so significant about that small orbiting mass, but it appears to be a subject people are quite intrigued by, just as the scientists who helped make its discoveries. Let’s demystify Pluto and take a plunge into the depths of the past to look into how its historical past has shaped what we know about it today.

Pluto’s discovery:

Today we know Pluto has been estimated to have a chemical composition of 70% rock and 30% frozen water (Choi). Its surface contains mountains as high as the Earth’s Rocky Mountains, and an abundance of ice ridges. It has even been speculated that Pluto has an ocean beneath its hard exterior. We have learned so much about Pluto since its discovery, but how exactly was it discovered?

Pluto’s discovery came to be all because of Percival Lowell, an astronomer with some unique perspectives (Bryson, 19-23). Those perspectives, not always appreciated by his family or the public. One of Lowell’s ‘out there’ theories that was immediately rejected from both the scientific community and everyone else pretty much involved industrial Martians on Mars that he claimed had advanced agricultural systems. Another one of his claims, a more plausible one, was that there was a ninth planet beyond Neptune. He spent a lot of the later years of his life searching for it.  

 

 

Percival Lowell (Public Domain)

After his death, the Lowell observatory hired Clyde Tombaugh in hope that he could prove that Lowell was right in there being a ninth planet beyond Neptune. Indeed, Lowell’s theory was correct! Tombaugh, who was not a professional astronomer, discovered Pluto after only a year of searching on March 13th, 1930 at the Lowell Observatory in Arizona (“March 13, 1930: Clyde” ).

Clyde Tombaugh (Public Domain)

Pluto’s name was actually chosen by 11-year-old Venetia Burney when Lowell Observatory was taking name suggestions for the new discovery. The name is that of the Roman god of the underworld. It was partly said to be chosen because the first two letters of the name are Percival Lowell’s initials, which honor him for his work that contributed to Pluto’s discovery (“How Pluto Got Its Name”).

Pluto- planet or not?

When Pluto was first discovered in 1930, it was classified as a planet (Mann).Though it was considered a planet, many people also called the orbiting object an ‘oddball’. Its orbit is so unique, in having a very non-circular pattern. In 1992, the Kuiper Belt was discovered, which Pluto is part of, along with a bunch of other icy worlds within the asteroid belt. Pluto had its planet status until 2006, when it was decided by the International Astronomical Union (IAU), that Pluto’s status is actually a dwarf planet (“Why Is Pluto No Longer”).

The definition of a planet has changed over time and has been widely debated. ‘What exactly defines a planet?’ scientists have asked themselves. In 2005, when the bodyEris was found, another member of the shared asteroid belt with Pluto, scientists really questioned what exactly defines a planet (Mann). They wondered if Pluto was indeed a planet, did that mean Eris and other objects in the belt qualified as planets as well? The IAU then got together to set out guidelines to what a planet exactly was. Three rules were the deciding factors: It must orbit around the sun, it has to have enough mass to become a nearly round object, and lastly, it has to “clear...its neighboring region of other objects (“Why Is Pluto No Longer”). “Clearing its neighboring region of other objects” basically means that the planet has gravitational dominants in space. The third and final rule regarding gravitational dominants was unfortunately the criteria Pluto failed to meet and led to its demise as a planet.  

The discovery of Charon:

The discovery of Pluto’s biggest and closest moon all happened in the same city in Arizona where the planet itself was first discovered, Flagstaff (Bryson)! Crazy, isn’t it? It all started with James Christy, an astronomer who worked at the U.S Naval Observatory. In 1978 while doing some routine scans, Christy saw a small dot next to Pluto, and realized, Pluto must have a moon! When he first discovered the moon, he brought his colleague Robert Harrington in to confirm what he found. The moon was named Charon, suggested by Christy, the discoverer himself (“Charon: In Depth”). The name Charon refers to the ferryman that carries souls across the river Acheron in the underworld that the Roman god, Pluto, rules. Christy also suggested the name because the first four letters matched his wife’s.

James Christy and Robert Harrington (US Navy)

The moon Charon is half the size of Pluto, and is huge enough that Pluto and Charon are considered a double dwarf planet system- the only known occurrence of one in the solar system (“Charon: In Depth”). Charon and Pluto’s relationship is also quite special in the way that Charon is tidal locking Pluto. Tidal locking is the name of the phenomenon that occurs when a certain side of the moon continuously faces its planet. It also floats over the same spot on the planet as it rotates. Basically, Charon never rises or sets in Pluto’s sky (Lehnardt). A common misconception about Charon is that it orbits Pluto- which in fact, it does not. Both Charon and Pluto orbit a barycenter located above the surface of Pluto. A barycenter is basically a ‘common center of gravity’. It also has been discovered that Charon’s surface is covered in frozen water containing nitrogen, methane, and carbon dioxide. It will be exciting to see in the future what is discovered about this curious moon, seeing as it has been said it contains signs that life could occur there.

 

Charon (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker)

The rest of the moons:

So we’ve heard about Pluto, and his close friend Charon, but what about his other nearby pals? Including Charon, Pluto has 5 satellites total (Sharp). 

Comparison of Pluto's moons sizes (NASA/JHUAPL/SwRI)

 In 2005, 2 smaller moons of Pluto, now named Nix and Hydra, were discovered with the NASA Hubble Space Telescope. These moons are two to three times farther from Pluto than Charon is. Both moons are quite unique and odd in shape. While Nix looks like a jelly bean, Hydra’s shape is said to resemble a mitten. The name Nix was chosen, as it was named after a mythological goddess of night and darkness. Hydra’s name was chosen because it is a nine-headed serpent guard within Pluto’s realm. The fourth and fifth moons of Pluto were found one year apart, 6 years after Nix and Hydra were discovered.

Kerberos —named after the three-headed dog that guards Hades— was discovered first in 2011 using the Hubble. The satellite was found to have two lobes, one five-mile-long, and a three-mile-long. In 2012, Styx —named after the river separating the world of the living from the realm of the dead— was found. It can be identified by its very irregular shape.

Hydra rotates the fastest out of the moons, making a full spin amazingly every 10 hours. With its 38 day orbit of Pluto, Hydra spins a total of 89 times. Nix, Kerberos, and Styx, spin about 6-10 times per orbit, which is still considered quite fast. The rapid speed of Pluto’s moon’s orbit is quite surprising to scientists, as they thought that Pluto’s gravity would have slowed down their rotation.

 

Pluto and beyond:

It seems that Pluto and its moons still hold many mysteries that scientists are eager to figure out and explore. Who knows what will be discovered next, or what will change about the definition of what exactly a planet is… Do you think Pluto should be considered a planet? What do you think it should be classified as? Let me know in the comments!

Purple = image  

Works Cited

Bryson, Bill. A Short History of Nearly Everything. Broadway Books, 2003.


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“Clyde Tombaugh, Discoverer of Pluto, with His Homemade Telescope 1930.” Wikipedia, Wikipedia, 30 Apr. 2012, en.wikipedia.org/wiki/Clyde_Tombaugh#/media/File:Clyde_W._Tombaugh.jpeg.

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Lehnardt, Karin. “30 Spectacular Facts about Charon.” Fact Retriever, Fact Retriever, 5 Sept. 2019, www.factretriever.com/charon-facts.

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