It used to be that My Very Excellent Mother Just Served Us Nine Pizzas. Alas, pizza is no longer for dinner.

It was 2006 when Pluto was demoted from our solar system’s 9th planet and renamed a dwarf planet (or more accurately a “pluton”) by the International Astronomical Union (IAU). The mnemonic we all memorized in 4th grade became outdated and my world was shaken. The kids we teach now were just wee ones when this change in nomenclature was made, so it gives me a feeling of warmth inside when students still know about the little guy today.

But why was it kicked out of the club after so many years? Well, NASA may not be up and running at the moment (Government shutdown, 2013…NASA was affected!), so I’m here to tell you why.

What: In the early 2000’s a celestial body named Eris was found to exist in the same belt as Pluto and was larger in mass. This exciting news about a possible 10th planet (and then possibly an 11th and 12th considering the other large celestial bodies found around the same time) led to the IAU to reboot the definition for the 21st century since such strides in science had made it easier to find objects lightyears and lightyears away.

According to the IAU, what now makes a planet a planet is that it follows these rules:

1. “The object must be in orbit around a star while not being itself a star.”
2. “It must be large enough (or more technically correct, massive enough” for its own gravity to pull it into a nearly spherical shape.”
3. “It must ‘clear its neighborhood’ of smaller objects around its orbit.”

So What: Unfortunately poor Pluto didn’t make the cut. It both orbits around a star and is nearly spherical in shape, but doesn’t “clear its neighborhood.” In other words, if something comes into the orbit of an object, its gravity must be strong enough to pull it in or completely expel it. Pluto isn’t big or strong enough to sweep it’s own streets, so a full fledged planet it ain’t.

However according to the IAU website, if one were to ask, “is Pluto a planet?” the answer would kind of still be yes. Pluto is a dwarf planet. In fact, one could say that we have 12 planets—5 of them being dwarf.

Now What: Does it really matter what we decide to call the celestial bodies of our solar system? Maybe. Maybe not. It may be that in a few years the IAU will have to come up with an even stricter definition for planet as science continues forth in its quest to classify anything and everything. Not to say that naming and classifying isn’t important, but it doesn’t change what’s out there.

So, semantics-shmantics, Pluto will always have a special place in my heart.

At High Trails Outdoor Science School, we literally force our instructors to write about elementary outdoor education, teaching outside, learning outside, our dirty classroom (the forest…gosh), environmental science, outdoor science, and all other tree hugging student and kid loving things that keep us engaged, passionate, driven, loving our job, digging our life, and spreading the word to anyone whose attention we can hold for long enough to actually make it through reading this entire sentence. Whew…. www.dirtyclassroom.com