Growing up, children were raised on the notion that our solar system comprises nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and, last but not least, Pluto.
With such a vast unknown universe existing unexplored, it was easy for the minds of children to take comfort in the bits of knowledge that were accepted. The foundation of studying space back then, which almost all of our astronomy-related subjects in elementary school were built on, was this nine-planet solar system.
In 2006, the declaration that Pluto was not a planet and we actually only had eight planets seemed incongruous.
The demotion of Pluto sparked widespread debate and is still discussed today. Recently, however, scientists have redefined the taxonomic identification of a planet. In other words: Pluto may be reinstated as a ninth planet.
Pluto was discovered in 1930 by astronomer Clyde Tombaugh. Initially, Pluto was known as the smallest planet in our solar system. It is the farthest from the sun and is about 7.5 billion kilometers from Earth.
Pluto is unique in that its orbit around the sun is different from the elliptical orbit of all the other planets. Thus, it can be seen as being closer to the sun than Neptune at times.
Since Pluto is so far away, the region beyond the orbit of Neptune and surrounding Pluto is called the Kuiper belt. This “belt” consists of comets, asteroids and frozen gases.
In 2005, astronomer Michael E. Brown believed he discovered another planet, adding on a 10th to the solar system.
This caused the International Astronomical Union to decide to come up with a clear definition of the term “planet.” By 2006, there were clear conditions that a celestial body had to meet before being deemed a planet.
First, it must orbit around the sun. Second, it must have enough mass that its own gravitational force shapes the planet into a sphere. Third, there must not be any other object within its orbit that it does not control with its gravity. Using this criteria, Brown’s planet did not meet these standards.
Similarly, since Pluto’s orbital was shared by other objects in the Kuiper belt, Pluto was demoted to a “dwarf planet.”
Thirteen years later, an astronomer from the Florida Space Institute, Philip Metzger, claimed that none of the scientific literature from the past 200 years supported the third requirement that a planet needed to control all objects in its orbital space.
Metzger said, “It’s a sloppy definition … we now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it’s functionally useful.”
According to him, no planet necessarily controls everything in its orbit evidence for this simply is not valid. A planet’s definition should not rely the dynamic it has with objects in its orbit, but rather its permanent, intrinsic properties.
Metzger emphasizes the second requirement, which is whether or not the planet in question has enough mass for its gravity to shape the planet as a sphere.
Based on his research, he explains that this phenomenon actually leads to active geology on the planet. His research also indicates that Pluto should be reinstated as a planet and recognized as one of the most complex yet fascinating planets in the solar system.
While these reclassifications may not have a direct effect on people, they do suggest the breadth of ambiguity and mystery that exists on so much of the universe’s unchartered territory. Pluto being reinstated as a planet is proof that the purpose of science is not to set in stone well-established facts but to continue challenging every proposal.
Science is about constantly evolving and rectifying theories as new evidence is introduced. It is crucial to continue seeking information, push beyond our intellectual awareness and question everything, no matter the size of what’s in question.
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