The Pluto Files: Is Pluto a Planet?
- Natalie Lee
- Jul 17, 2020
- 4 min read
Is Pluto a planet? This is a question that astronomers had debated for years before coming to a consensus. In his book The Pluto Files, Neil deGrasse Tyson, a revered astrophysicist, follows Pluto’s journey from its discovery to its demotion. Although the book was published in 2009 and may not have the most up-to-date information about Pluto, it’s still a fantastic read filled with intrigue and quirky humor.
The discovery of Pluto didn’t start with Pluto at all; it started with Uranus. The 7th planet from the Sun was the first planet discovered since ancient times. However, its orbit was rather strange. Scientists concluded that there must be something else beyond Uranus that was affecting its orbit.
Let me go on a tangent and briefly explain how gravity works. Every mass has a gravitational force that pulls other masses towards itself. The larger the mass, the stronger the force. The Earth is much larger than an individual human, so humans are bound to Earth by Earth’s gravity while the gravitational force of a human has no effect on the Earth. Gravitational force is why the moon orbits the Earth and why the planets orbit the Sun.
Back to the story, astronomers believed that if Uranus’s orbit wasn’t normal, something else must be pulling it off course. This led to the birth of “Planet X,” the mysterious “undiscovered” object, and the hunt was on. Scientists were elated by the discovery of Neptune, but none of the evidence stacked up. Neptune was not the Planet X they were looking for. The search went on.
Finally, at around 4:00 PM on February 18th, 1930, Clyde W. Tombaugh found Pluto in the sky. The 24-year-old astronomer believed he had achieved his goal of locating Planet X. However, scientists realized that Pluto’s mass was too small to affect Uranus’s orbit. After over a century of scouring the solar system, Planet X happened to be nonexistent.
Fun fact: At one point, scientists believed that Pluto would disappear from the solar system in 1984. Of course, this turned out to be false.
Here are some quick Pluto facts:
Pluto is about 70% rock and about 30% ice by mass (how much matter is in an object).
However, Pluto is about 45% rock and about 55% ice by volume (how much space an object takes up) because rock is denser than ice.
Pluto is less than 5% of Mercury’s mass.
Pluto has a non-circular orbit; instead, it is elliptical.
Pluto and Charon (one of its moons) are double-tidally locked, which means the same side of Pluto will always face Charon and vice versa. This double-tidal lock is due to the fact that Charon is almost as large as Pluto. Instead of Charon orbiting Pluto like the Moon orbits Earth, Charon and Pluto orbit a point in space between them.
Fun Fact: The Moon has been tidally locked by the Earth, so we always see the same side of the Moon.
Pluto and Neptune in a three-to-two orbital resonance: “For every three trips around the Sun that Neptune takes, Pluto takes exactly two…” (37)
Pluto is technically part of Kuiper Belt, which is the outer region of the solar system beyond Neptune.
Pluto’s planet status came into question when other objects in the Kuiper Belt were discovered. Astronomers predicted that there would be at least ten objects that would be larger than Pluto: should those objects also be called planets?
With a mass of roughly 1.27 x 10^22 kilograms and a radius of 1,137 kilometers, Pluto is much tinier than Earth. Even Mercury is bigger than Pluto in terms of both mass and size. Pluto also doesn’t fall into one of the planetary categories. The inner planets of the solar system were considered the “terrestrial planets” due to their rocky terrain while the outer planets were named the “gas giants” due to their size and composition. Pluto was neither; it was an icy body that resembled many of the objects found in the Kuiper Belt.
Tyson himself hosted a 90-minute panel debate to discuss Pluto’s planethood. On May 24th, 1999, Pluto was removed from the Rose Center for Earth and Space (part of the American Museum of Natural History) of which Tyson was the director. After even more debate, Pluto was demoted to a dwarf planet on August 24th, 2006. In the months to follow, he would receive countless emails and letters of outrage about Pluto’s removal from the exhibit and its demotion. The senders ranged from young 1st-graders to elderly citizens. Tyson includes several of these letters in his book, and they are quite enjoyable to read. It was interesting to see how a single planet could stir up such emotion. Some even wrote songs about “Pluto’s fall from grace,” as Tyson calls it; a few of these songs can be found in the appendix of the book.
Out of all the commotion, two new words were born: Plutocracy (noun) and to pluto (verb). “Plutocracy [is] government by the wealthy” (15). “[T]o pluto [or] to be plutoed [means] to demote or devalue someone or something” (147).
Tyson’s wit accompanied by hilarious cartoons throughout the book made it entertaining to read. It is clear that although he, with a heavy heart, agreed with the denouncement of Pluto, he deeply respects other people’s opinions, whether the person is a colleague or a complete stranger. There’s no question that Pluto has been through a lot since its discovery. I hope you learned something new today! Keep a lookout for the next post!
Vocab That I Learned
Haberdashery (noun): a men's clothing shop
Spate (noun): a larger number of events than usual, especially unpleasant ones, happening at about the same time
Oblong (adjective): having an elongated shape, as a rectangle or an oval
Pedagogy (noun): the method and practice of teaching, especially as an academic subject or theoretical concept
Innocuous (adjective): not harmful or injurious; harmless
Scatology (noun): an interest in or preoccupation with excrement and excretion (Wikipedia puts it more simply as the study of feces)
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