Space and Physics
PUBLISHED
NASA Administrator Jared Isaacman has responded to the letter of a 10-year-old space enthusiast in which she pleads with him to make Pluto a planet again. The letter, posted by X account Mike's Weather Page, is short and to the point.
"Please make Pluto a planet again. I really want it to be a planet again," it begins. "Here are some reasons that Pluto should be a planet again: 1) it is part of our solar system and used to be a planet. 2) It is a dwarf planet and deserves to be an actual planet 3) It might make a lot of people happy."
Kaela, 10 years old, goes on to list a few Pluto facts to show she has knowledge of the dwarf planet, which she correctly identifies as residing in the Kuiper Belt.
"It might not be your choice but if it is please please please make it a planet," she adds. "It would make me very very very happy. If you can't make it an actual planet please consider it a planet."
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So, if it would make everybody much happier, why isn't it a planet? And why was it considered one in the first place? To find out, we must go back to the start of the 20th century.
At that time, US astronomer Percival Lowell believed there were discrepancies in the orbit of Uranus and Neptune that could be explained by the pull of an as-yet-unknown planet in the Solar System.
In 1905, he made predictions about its orbit, and based on these and the predictions of other astronomers, Pluto was eventually located in 1930 by Clyde Tombaugh.
The discovery was made 14 years after Lowell’s death, but he was still a part of it; Tombaugh had spotted the object from the Lowell Observatory in Flagstaff, Arizona, which Percival had founded in 1894.
Tombaugh used a blink comparator, a device that quickly flipped between two images of the same area of sky, allowing any slight differences to be noticed more easily. By looking at the area of sky where Lowell’s mysterious extra planet was predicted to be, he found an object that made suspicious movements between January 23 and 29, 1930.
It was Pluto, a name it received shortly afterwards from Venetia Burney, an 11-year-old girl from Oxford, England, who wrote to the Lowell Observatory with the suggestion.
But Pluto was only briefly a planet. Before it could make a single full orbit after its discovery (one Pluto year lasts for 248 Earth years), it was demoted to a dwarf planet on August 24, 2006. While "planet" is still right there in the name, there are many people who are unhappy about the change. So why was it made?
The issue was that astronomers had, in the intervening years, discovered a number of other planet-like objects in the Solar System, including Eris, Haumea, Makemake, and Ceres. Out in the Kuiper belt, there is also Gonggong, Quaoar, Sedna, and Orcus to think about. Some of these, particularly Eris, are around the same size as Pluto, leading astronomers to discuss what constitutes a planet.
On that fateful day in 2006, the International Astronomical Union (IAU) came to an agreement. According to the definition it adopted, a planet must orbit a star (a little contentious now that we know of many rogue planets outside the Solar System) and have enough gravity to force itself into a spherical shape. Lastly, and this was the part that led to the downgrade in Pluto's status, it must be large enough that it has cleared its orbit of any smaller objects in its path around the Sun.
Pluto, unfortunately, doesn’t dominate its orbit, instead sharing it with many other objects. This makes it a dwarf planet, or sometimes even a "double planet," which seems cool enough to be going on with.
"Pluto is orbited by five known moons, the largest of which is Charon,” NASA explains. “Charon is about half the size of Pluto itself, making it the largest satellite relative to the planet [interesting choice of word, NASA] it orbits in our solar system."
"Pluto and Charon are often referred to as a 'double planet'," it goes on to say.
NASA administrator Isaacman replied to the letter on April 9, saying "Kaela - We are looking into this," though we hope she can be satisfied with calling it a dwarf planet or a double planet. As she correctly identified in her letter, this isn’t something in Isaacman's jurisdiction, and astronomers will continue to use a definition of planets that they find useful, even if it means that Pluto can't be in the club anymore.
