Audience: Middle and High School Students
Sometimes Pluto is closer to the Sun than Neptune is. Photo by NASA from Unsplash.
Orbiting the unimaginably hot Sun is our solar system, which houses eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. But did you know that we used to have another planet beyond Neptune? This former planet is called Pluto. Being 2253 kilometers (1400 miles) in width, its size is only about half the width of the United States! Because of its distance from Earth (39 astronomical units or 3.7 billion kilometers from the Sun), Pluto remains a mystery to us. Could Pluto be a future home for humans, or does its distance from the Sun render this idea impossible?
Its Discovery
The existence of a ninth planet in our solar system was first proposed in 1902 by Percival Lowell, an American astronomer, after he identified certain irregularities beyond Neptune and credited them to a new, undiscovered planet. Three years later, the search for this proposed planet began. At first, this search consisted of capturing images of the sky and checking the images for evidence of the planet. Thankfully, this guess-and-check method of search was improved upon with the acquisition of better telescopes and computers, which helped predict the location of the planet. On February 18, 1930, astronomer Clyde Tombaugh discovered Pluto using a device called a blink comparator machine. This machine worked by taking photos of the night sky at the same time two nights in a row and placing these images side-by-side on viewing plates, which are flat surfaces on the comparator that allow light to shine through. From these plates, the images are projected, flashing alternately into one central viewing eyepiece (where the viewer makes observations). From here, the observer can determine the differences in the photos, and therefore, what has moved. Pluto’s discovery was announced to the world on March 13, 1930, on what would have been Percival Lowell’s 75th birthday.
Why is it called Pluto?
In 1930, the Lowell Observatory received 1,000 suggestions worldwide for the name of their newly discovered planet. Even with all these suggestions, it was actually an 11 year-old girl named Venetia Burney who was responsible for naming the planet. She suggested the name to her grandfather, who sent the proposal to Lowell Observatory. So, why Pluto? The name comes from the Roman god of the underworld of the same name, which keeps to the theme of the other mythology-based planets in our solar system. The name also honours Percival Lowell, as the first two letters of the planet correspond to his initials.
Features of Pluto: Could it Support Life?
Pluto is made up of a rocky core, with an ocean of water deep inside, covered by a layer of glacier. Its crust is mostly composed of nitrogen ice, giant mountains of water ice, and some methane and carbon monoxide ices. Its atmosphere is composed of nitrogen, methane, and carbon monoxide. Due to its distance from the sun, temperatures on Pluto can drop to around -240 degrees Celsius or -400 degrees Fahrenheit. So, what does this mean for our future? Despite the possibility of Pluto’s interior having a large body of water and having warmer temperatures, the possibility of Pluto sustaining human life is unlikely. Pluto is far too cold, has a lack of breathable air and sunlight, and does not have other lifeforms to sustain us.
Other Features of Pluto: What Makes It Special?
On Pluto’s surface is a large heart-shaped region made of various materials, including carbon monoxide ice, which is poisonous to humans in its gaseous state. This region is unofficially known as the Tombaugh Region. Orbiting Pluto are five moons, known as Charon, Styx, Nix, Kerberos, and Hydra. Charon is the largest, being nearly half the size of Pluto, and is the closest to the planet. Because of the moon’s size, Charon and Pluto actually orbit around a space that lies between the two.
Its Reclassification
NASA defines a planet as having the following three characteristics:
Orbits the Sun.
Nearly round shape.
Gravitationally dominant (no other celestial objects of a similar size in its path.)
Because of its largest moon, Charon, Pluto does not meet the third characteristic above. In 2006, Pluto was reclassified from being a planet to being a dwarf planet.
Mission to Pluto
There has only been one mission to Pluto and its moons, called NASA’s New Horizons mission. It was launched in January 2006 and made its closest approach to Pluto on July 14, 2015. In October 2021, it returned the first close-up images of Pluto and its moons. Throughout its trip, the mission has also made observations of Jupiter, the Kuiper Belt (a region of the Solar System beyond Neptune), and a number of moons. As of yet, there are no known future missions to Pluto being planned.
At this point in time, the future of Pluto is unknown. Will we find a way to colonize such a cold celestial body? Will something happen to Charon to result in Pluto being reclassified as a planet? Will NASA change its definition of a planet? Unfortunately, due to its distance and inability to assist us, we likely won’t have answers to these questions soon, but no matter what happens to Pluto, it will always be loved and remembered as our honorary “ninth planet.”
Bibliography:
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