Why Pluto Is Not a planet?

Among all the planets, Pluto's story is perhaps the most fascinating. In the mid-19th century, astronomers noticed irregularities in the orbits of Uranus and Neptune. They hypothesized that these anomalies were caused by the gravitational pull of an unknown planet beyond Neptune. They named this mysterious object "Planet X" and began searching for it.

Although images of Pluto were captured in 1915 and again in 1919, they were dismissed because it appeared very small and dim. Astronomers were expecting to find a much larger planet, one that could explain the gravitational effects on Uranus and Neptune.

Interest in the search eventually faded, especially after Percival Lowell, who had led the effort, passed away in 1916. The enthusiasm gradually diminished.

However, in 1929, the Lowell Observatory in Arizona resumed the search for Planet X. A 16-inch telescope and camera were used to photograph the sky, and a young amateur astronomer named Clyde Tombaugh was assigned to the task.

Clyde Tombaugh’s life is as extraordinary as Pluto's own tale. From a young age, he was fascinated by stars and planets. He used a small telescope belonging to his uncle to stargaze. Later, he built his own 8-inch reflector telescope, marking the beginning of his lifelong passion for telescope making—eventually building nearly 40 of them.

In 1928, he built a 9-inch reflector telescope. He planned to start studying astronomy at a university, but that same year, a severe hailstorm destroyed his family’s crops, causing a financial crisis that crushed his dreams of formal education. Instead, he helped with farming during the day and gazed at the stars at night. He made meticulous drawings of planets like Jupiter and Mars and sent them to the Lowell Observatory. Impressed by his work, the observatory offered him a job. Though they couldn't afford a professional astronomer, Tombaugh was hired at a modest wage due to his clear passion and skill.

Tombaugh began work with great enthusiasm, although the job itself was tedious: taking photographs of the sky section by section, looking for signs of Planet X. Finally, on February 18, 1930, his efforts paid off. He discovered a small moving dot on a photographic plate—an unknown object in motion, a new planet. A month later, its discovery was officially announced, and the object was named Pluto, after the Roman god of the underworld, fitting since it was so far from the Sun that barely any light reached it.

The young amateur astronomer instantly rose to fame, despite not having a university degree. A university later offered him a scholarship, and he enrolled in 1932. By 1939, he had earned both bachelor’s and master’s degrees and remained dedicated to astronomy for the rest of his life.

However, Pluto's discovery did not solve the mysteries—it introduced new ones. The main issue was its small size. Pluto has a diameter of only 1,375 miles, just one-fifth that of Earth. Moreover, its orbit is highly irregular. At its farthest point from the Sun, it is 4.5 billion miles away, and at its closest, just 2.7 billion miles. At times, it even crosses inside Neptune’s orbit—something no other planet does. Most planets orbit in a relatively flat plane, but Pluto's orbit is tilted at 17 degrees to this plane, making it unique.

Additionally, in our solar system, there is a pattern: the inner four planets are rocky, and the outer ones are gaseous. Based on its distance, Pluto should be gaseous too, but it isn’t. It takes Pluto 248 Earth years to complete one orbit around the Sun. A single day on Pluto is equivalent to 6 Earth days and 9 hours. Due to its great distance from the Sun, its surface temperature ranges from -212°C to -228°C.

Because of its remote location, astronomers knew very little about Pluto. So, they were astonished when they later discovered it had a moon. This moon, Charon, is especially unusual because it is half the size of Pluto and only 12,000 miles away. No other planet in the solar system has such a large moon relative to its own size.

As astronomers continued exploring the solar system, they discovered another object even larger than Pluto, located farther out. It was named 2003 UB313, now known as Eris. This raised a critical question: If Pluto is a planet, shouldn’t Eris also be considered one?

This led the International Astronomical Union (IAU) to hold an emergency meeting and redefine what qualifies as a planet. According to their new definition, a celestial body must meet three criteria to be considered a planet:

1. It must orbit the Sun.

2. It must be spherical due to its own gravity.

3. It must have cleared its orbital path of other debris.

Pluto met the first two conditions but failed the third. It shares its orbit with many other objects and has not cleared its path like the other planets. Therefore, Pluto lost its planetary status and was reclassified as a "dwarf planet." There are now 44 known dwarf planets in our solar system.

However, not all astronomers agree. Many continue to debate the issue and are reluctant to demote Pluto, which held planetary status for so long. NASA even sent a spacecraft to study Pluto and Charon, which arrived in 2015, reigniting interest in these distant worlds. Despite its reclassification, Pluto holds a unique place in both scientific and popular imagination.

Textbooks and planetariums have begun removing Pluto from the list of planets. Understandably, many people feel sentimental about this change. A planet that captured the world’s attention for decades is now grouped with over 40 other lesser-known dwarf planets. But science must follow reason and evidence, even when it challenges our emotions.

So, farewell Pluto—we will miss you!