On August 24, 2006 Pluto died1. Okay maybe it didn’t exactly die, but Pluto the planet died and Pluto the dwarf planet was born. I remember hearing the news in the beginning of grade five and I was FURIOUS. Not because of Pluto’s demotion, but because my mnemonic for memorizing the planets names no longer made sense. “My Very Educated Mother Just Served Us Nine Pizzas” had become “My Very Educated Mother Just Served Us Nine.” Nine what?!
Planet Mnemonic
Source: Simplyilka. http://simplyilka.com/2014/10/23/5-science-jokes-everyone/ (accessed Oct 16, 2016)
The decision to demote Pluto was very controversial, many scientists and people, including myself, saw the nine planets as fixtures in the sky that represented our small section in the universe. So why did Pluto get demoted after 75 years of being a planet and why was the decision so controversial?
Pluto Controversy
Source: http://www.redbubble.com/people/alliejoy224/works/14585362-you-heard-about-pluto?p=poster (accessed Oct 16, 2016)
Unlike all the other planets Pluto was an oddball to begin with. Pluto’s eccentric orbit crosses Neptune’s orbit for about 20 years out of its 248 year orbit2. No other planets cross orbital paths! The only other objects that do, are comets and asteroids.
In 2005, Caltech astronomer Mike Brown aka Pluto Killer announced the discovery of Eris, an object in the Kuiper belt that was similar in size to Pluto3. NASA defines the Kuiper Belt as “a disc-shaped region of icy bodies- including Pluto- and comets beyond the orbit of Neptune4.” So if we considered Pluto a planet then Eris would have to become the tenth planet. However, since the discovery of Eris, more objects in the Kuiper Belt were identified as having masses comparable to Pluto. That’s when the International Astronomical Union (IAU) had to step in and redefine the term planet.
Other Objects in the Kuiper Belt
Source: Amos, J. Pluto flyby: Meet the ‘King of the Kuiper Belt,’ BBC News. http://www.bbc.com/news/science-environment-33500681 (accessed Oct 16, 2016)
The new definition of planet needs to meet three criterion5: (1) must orbit the sun, (2) have sufficient mass to be round, or nearly round, (3) has cleared the neighbourhood around its orbit.
Unfortunately Pluto did not meet the last criterion because it shares its orbital neighbourhood with other objects in the Kuiper belt. Alan Stern, leader of NASA’s New Horizon mission, along with many other scientists were not happy with this new definition of planets. Stern told SPACE.com. “A river is a river, independent of whether there are other rivers nearby. In science, we call things what they are based on their attributes, not what they’re next to3.” However Stern may have some bias on the subject because he was leading the New Horizon Mission to Pluto, which was launched in early 2006. Leading a launch to a planet is much more exciting then leading one to a dwarf planet.
After doing all of this research and understanding the arguments each side was making, my opinion on Pluto’s status as a planet changed. Although it would be nice for my mnemonic of the planets to make sense, our knowledge of the universe is constantly changing and evolving, and along with it definitions for our universe need to change too.
Until our next journey, live long and prosper…unless you’re Pluto
By: Flora Iranmanesh
References:
(1) Inman, M. Pluto Not a Planet, Astronomers Rule. National Geographic [online], August 24, 2006. http://news.nationalgeographic.com/news/2006/08/060824-pluto-planet.html (accessed Oct 16, 2016)
(2) Spaleta, S. Neil deGrasse Tyson’s Case Against Pluto’s ‘Planet-hood. video file, Space.com, July, 14 2015. http://www.space.com/29949-neil-degrasse-tyson-s-case-against-pluto-s-planet-hood-video.html (accessed Oct 16, 2016)
(3) Wall, M. Five Years Later, Pluto’s Planethood Demotion Still Stirs Controversy. space.com [online], August 24, 2011. http://www.space.com/12709-pluto-dwarf-planet-decision-5-years-anniversary-iau.html (accessed Oct 16, 2016)
(4) Solar System Exploration NASA Science, Kuiper Belt: Overview. http://solarsystem.nasa.gov/planets/kbos (accessed Oct 16, 2016)
(5) Howell, E. What Is a Planet? space.com [online], May 22, 2014. http://www.space.com/25986-planet-definition.html (accessed Oct 16, 2016)
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