Why Is Pluto No Longer a Planet?

Before 2006, if you went to elementary or middle school, you might have learned that there were nine planets in the solar system. Mercury was the Sun’s nearest neighbour, while Pluto was its furthest neighbour. Solar system models began to diverge after 2006, however. Instead of nine planets orbiting the Sun, there are now just eight. After 2006, astronomers no longer considered Pluto to be a planet. So, what happened to Pluto?

The Discovery of Pluto

Pluto was discovered in 1930 by an American astronomer named Clyde Tombaugh. The press went crazy with enthusiasm and immediately began referring to it as the ninth planet in the solar system. He discovered it while searching for Percival Lowell’s “Planet X,” which Lowell had hypothesized would affect Neptune and Uranus.

Lowell was certain that there was a planet beyond Neptune that he had never heard of. Tombaugh’s discovery of Pluto matched this description. Soon after the discovery of this new planet, textbooks were republished with the new knowledge, as well as children’s cartoons and pop culture. Even the public had a say in what it would be called. Venetia Burney, a young girl, came up with the idea as part of the longstanding custom of attributing legendary personalities to celestial bodies.

In the 1970s, astronomers learned that Pluto’s mass had been underestimated. The researchers found Charon, one of Pluto’s moons, allowing them to improve their calculations. To their astonishment, they discovered that Pluto was just a sixth of the size of Earth. It’s not even the size of our own moon, much alone a planet. This was a game-changer.

What Exactly Is a Planet?

Astronomers discovered worlds of comparable size and mass in the 1990s, which caused some to dispute Pluto’s status as a planet. Another object orbiting the Sun beyond Neptune was discovered in 2005 by scientists. In terms of mass, this newcomer, named Eris, dwarfed Pluto. Astronomers have claimed that Eris, as well as other nearby objects, should be treated as if they were planets unto themselves. In contrast, the International Astronomical Union (IAU) is considering reclassifying all these objects. Until 2006, no one could agree on what exactly constitutes a planet. The International Astronomical Union (IAU) released an official definition of a planet in 2006. They looked at three factors:

  • The object must revolve around the Sun.
  • Because of the object’s gravitational force, a spherical form must be achieved.
  • The object must be big enough to move the debris out of orbit.

All the planets, from Mercury to Neptune, satisfy all three requirements, except Pluto. Pluto, although being spherical and orbiting the Sun, does not have the gravitational strength to rid its orbit of debris. By this definition, Pluto was demoted to the status of a “dwarf planet,” along with other objects of comparable mass.

Where Did The Conflict Begin?

Clyde Tombaugh, an American astronomer, discovered Pluto in 1930 while working at the Lowell Observatory in Arizona. The group’s ninth member was quickly added to the list of members in the textbooks. However, as the years passed, astronomers started to wonder whether Pluto was the first of several tiny, frozen worlds discovered beyond Neptune’s orbit. It was not until 1992 that the first “resident” of the Kuiper Belt was found. The University of Hawaii’s 2.24-meter telescope on Mauna Kea spotted the potential Kuiper Belt Object (KBO) 1992 QBI.

The Backlash

The backlash, on the other hand, took a more personal and emotional turn than anybody had anticipated. The people rallied with the underdog. People donned protest t-shirts and disseminated petitions. A whole new verb was coined to describe this process: Pluto. The 26th of August has been designated as “Pluto Demotion Day.”

What was it about it that was so upsetting? Would it have made a difference if Pluto had been downgraded as a Kuiper Belt Object sooner? While some scientists have joined the protest movement, many others agree that this clarification was a good thing and would help us to understand space better.

Pluto has received a lot of attention from scientists for an object so far away. There are five moons, an orbital period of 248 Earth years, and an atmosphere of primarily carbon monoxide, nitrogen, and methane. The surface temperature varies from -226° to -240°C. Pluto’s 5.9-billion-kilometre separation from the Sun contributes to its darkness, according to a NASA website: You may view what it looks like during high noon on Pluto by entering your location into the search bar. It’s a little on the dimmer side.

Was It the Conclusion to The Problem?

No, to sum it up. Several researchers initially questioned whether a planet could clear its orbital surroundings. Due to Earth’s proximity to around 12,000 asteroids, we must share our space with them. According to some, the IAU’s 2006 definition of a planet excludes Earth, Jupiter, and other planets. New Horizons lead scientist Prof Alan Stern criticized the vote’s conclusion as “a horrible choice” and a definition that is “internally contradictory” shortly after it took place.

At the 10-day conference, barely 10% of the 2,700 scientists in attendance were present to vote on Pluto. Prof. Owen Gingerich from Harvard was the committee’s chairman. The vote was conducted on the final day of the General Assembly when many attendees had either departed or were about to fly out of Prague, which is why there was such a low turnout.

In television shows, literature, and public debates, the argument has continued ever since. Neil deGrasse Tyson was most recently challenged in 2014 by Alan Stern to a discussion on the subject of black holes. “I don’t have views that I expect other people to have,” said the second expert, who turned down the invitation. It is unlikely that the flyby of Pluto will give us any information that could change Pluto’s status. The word “planet” will be defined in a more precise way as a result of this.

Facts About Pluto:

  • Pluto is almost the same size as the moon.
  • Pluto’s orbit around the Sun takes 248 Earth years to complete. Pluto has not made a single orbit around the Sun since it was discovered in 1930 by astronomers. To put it in perspective, it has more than 150 years to go!
  • Light from the Sun takes over five hours to reach Pluto. Only eight minutes after the Sun’s rays leave the Sun, they reach Earth.
  • Pluto’s path is unpredictable. It is common knowledge that the planets in this solar system revolve around the Sun on a nearly flat plane. Pluto, on the other hand, makes an oblique 17-degree round around the Sun. The orbit is also very elliptical, crossing Neptune’s orbit.


No matter how reclassified, Pluto will always remain a fascinating place no matter what the new system says. For the first time ever, the New Horizons spacecraft flew past the Pluto system and sent the first high-resolution photographs of Pluto’s surface to humankind. New Horizons uncovered a new universe that no one had ever imagined. Liquid nitrogen rivers and lakes dot the landscape, as do vast ice plains and ice-covered mountain ranges. Pluto is no longer a planet, but that doesn’t mean it’s any less fascinating than any other eight bodies around the Sun.