Why Pluto isn’t a planet anymore


The night sky is a mystery and wonder that captivates and baffles people from the most ignorant novice of astronomy to experts in the field. Every day we are discovering more objects in our solar system and galaxies beyond. With the advances in technology, we are able to fly spacecrafts out to the most distant portions of our galaxy, the Milky Way. It was such advancements in technology and the discovery of extraterrestrial objects that led to the debate about Pluto’s planetary status. This unusual space rock has an interesting history and behavior, which makes it one of the more fascinating bodies to study.

Photo: NASA

A brief history of Pluto

Pluto was officially discovered in 1930 by Clyde Tombaugh, but only after a massive expedition started by Percival Lowell in 1906 and carried on by his widow, Constance Lowell, after his death. Lowell had actually captured some images of Pluto in 1915, but he was unable to recognize it. His long search for what he called “Planet X” was preceded by several astrophysicists before him. Pluto received its name from an 11-year-old girl at the time, Venetia Burney. It was named after the Roman god of the underworld.

Some more interesting facts about Pluto

Pluto takes nearly 250 Earth years to complete its orbit around the Sun and has an average temperature of -380 degrees Fahrenheit. It has 5 moons, despite it being smaller than our own moon, and is composed mainly of nitrogen ice. When it gets closer to the sun, the ice melts and forms a thin atmosphere, but when it moves away, it freezes as a solid again. Imagine Earth’s atmosphere changed like that…ֳSo what makes a planet a planet?

Despite all of its magnificent features, Pluto is not officially a planet, as decided in 2006 at the International Astronomical Union conference in Prague. This union is also responsible for coming up with the criteria for planetary status, namely:
A planet must orbit the sun independently (and not around another celestial body)
The gravity of a body must be strong enough to pull it into a spheroidal shape
A planet must be the largest object in its orbit

Pluto lost its planetary status because it crosses the orbit of Neptune and thus its relative mass is much lower than objects in its orbit path.

Photo: NASA

So what is Pluto then?

A month after the conference which stripped Pluto of its elite status, it was decided that objects which pass the first two criteria of planetary status would be known as dwarf planets, which is what Pluto’s designation remains today. There was fierce debate about its reclassification, with some suggestions of it being classified as a Kuiper belt object (the Kuiper belt is a sort of asteroid belt near the edge of the solar system that houses many space bodies similar to Pluto).

The debate goes on…

Some experts are quick to point out that the decision to declassify Pluto as a planet was voted on by only a small portion of astronomers at the time (less than 5%). There is also the added confounder that the word planet does not only have a scientific definition, but a linguistic one as well, that evolves over time. Surveys conducted on the linguistic point of view show that Pluto would fit into the definition given by the vast majority of respondents. Debates still continue between professional astronomers and other members of society to this day.