Pluto was discovered in 1930 and was considered the ninth planet of the solar system for over seventy years.
However, in 2006, the International Astronomical Union (IAU) decided to change the definition of a planet and downgrade Pluto to a dwarf planet. What was the reason behind this controversial decision?
The IAU is the organization responsible for naming and classifying celestial bodies, such as stars, planets, asteroids and comets. In 2006, the IAU held a general assembly in Prague where they voted on a resolution that defined a planet as a celestial body that:
– is in orbit around the sun,
– has enough mass to take on an almost round shape,
– and has cleared the neighborhood around his job.
By this definition, Pluto was ineligible as a planet because it shares its orbital environment with other icy objects in the Kuiper Belt, an area beyond Neptune that contains thousands of small, frozen bodies.
Pluto is also smaller than some of these objects, such as Eris, which was discovered in 2005 and sparked debate over Pluto’s status.
The IAU’s decision was not universally accepted by astronomers and the public, who felt Pluto deserved to retain its planetary status for historical and sentimental reasons.
Some argued that the IAU’s definition was too narrow and arbitrary, and that there could be other criteria for classifying planets, such as their geology, atmosphere, or potential for life.
However, the IAU’s decision also reflected advances in technology and knowledge that have revealed the diversity and complexity of the solar system.
By recognizing Pluto as a dwarf planet, along with four other similar objects (Ceres, Eris, Haumea, and Makemake), the IAU recognized that there are different kinds of worlds that deserve to be studied and appreciated for their own characteristics.
In 2015, NASA’s New Horizons mission flew past Pluto, capturing stunning images of its surface features, such as mountains, glaciers and a giant heart-shaped plain. The mission also revealed that Pluto has five moons, including Charon, which is nearly half that size.
Pluto may not have been a planet seventeen years ago, but it is still an important and beloved member of the solar system family.
