Science Week – Pluto: To be, then not to be, a Planet

Remember learning the names of the nine planets of the solar system back in elementary school? Did you memorize them with the phrase “Man Very Early Makes Jars Stand Up Nearly Perpendicular”? You may not be that old yet, but things have already changed. Since 2006, children are taught that “Man Very Early Makes Jars Stand Up Neatly”. Science advances at alarming rates, and Generation Y is no stranger to technology and innovation. 90’s babies have lived through change at a quicker pace than any other generation. In the first twenty years of their lives, they’ve seen computers go from being absent in most households to becoming a ‘necessity’ of modern life that can be held in the palm of one’s hand; they’ve watched pennies disappear; they’ve seen paper bills be exchanged for plastic money; they’ve witnessed DVD’s take over VHS cassettes, then be replaced by Netflix; and they were the last generation to learn that there were nine planets in the solar system. Today’s children grow up with one less name to memorize in grade-school science courses: Pluto.

During Vanier College’s annual Science Week, from March 21^st to March 24^th, Dr. Don Hetherington presented a talk called Pluto: to be, then not to be, a Planet. Hetherington, who used to teach at Vanier, discussed the reasoning behind Pluto’s demotion from ‘planet’ to ‘dwarf planet’. Most of the students attending the event were from science programs, but the ex-teacher’s explanations were well adapted to be understood by anyone and everyone. He pointed out that, as in any other domain, much of science is determined by conventions that are agreed upon by specific committees of specialists. Thus, at the International Astronomical Union (IAU) General Assembly in 2006, a definition of the term ‘planet’ (which is still somewhat controversial) was created in order to classify the celestial bodies in a more clean-cut manner. According to the IAU’s consensus, a planet can only be considered such if it meets the following three criteria:

• “A ‘planet’ is a celestial body that is in orbit around the Sun
• Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic (nearly round) shape
• Has cleared the neighborhood around its orbit”

At first glance, Pluto seems to correspond to the above definition. It is, however, delinquent with regards to the third criterion. Though Pluto’s orbit is clear of other spatial debris, astronomers have agreed that Pluto’s mass is not large enough to be responsible for the synchrony it has with Neptune (both orbits cross each other at two points – which, without synchrony, would lead to a collision). Neptune, which has a substantially larger mass, is thus accountable for keeping Pluto at a distance. This means that Pluto hasn’t “cleared the neighborhood around its orbit” by its own gravitational force.

Pluto, made up of ice, has never fit into the two categories of planets (the first four closest to the sun are the rock planets, while the farthest four make up the “Gas Giants”). Its orbit, inclined 30 degrees to those of the other planets, further distinguishes it from the first eight planets. It had always been an exception, a loner. Now, with its status as a dwarf planet, it fits in with many other celestial bodies – generally all within an area of the galaxy referred to as the “Kuiper Belt”.

Written By: Katherine Willcocks

March 2016

About The Author

Katherine Willcocks Kat has been dabbling in the art of the written word since childhood, dipping her toes in the world of photography every now and then. As a Vanier alumnus who studied in Communications, she explores Spoken Word Poetry, and, of course, journalism.