Pluto’s been making news again. Jared Isaacman, the head of NASA, recently suggested that maybe astronomers should rethink their decision to demote the world from a “planet” to a “dwarf-planet”. That decision was made back in 2006 and it led to lots of wailing. This included the cries of many little kids who’d just learned about the 9 planets and felt like cute little Pluto got a bum deal. Now Isaacman seems like a good guy and I sure don’t want to make little kids cry. Still, there’s an amazing science reason why Pluto got kicked out of the planet club.

It’s all about the rest of the solar system .

It was only a few decades ago that we thought the solar system ended when you ran out of planets. We knew about the inner solar system where the “rocky” planets lived: Mercury, Venus, Earth and Mars. We knew about the the outer solar system where the gas giant planets lived: Jupiter, Saturn, Uranus (no snickering) and Neptune. And, of course, way out there where the Sun looks like just another star, there was Pluto. As we all learned in school, those 9 planets make up the solar system.

Only they don’t. There’s more beyond Pluto and it matters.

In the vast darkness extending beyond ice-giant Neptune lies a whole lot of stuff. Most important for today is the Kuiper Belt reaching from just beyond Neptune out to almost twice the size of its orbit. The Kuiper Belt is basically construction debris left over from the assembly of the solar system. Its made from pieces of rock and ice that could have become planets but didn’t.

We didn’t know much about the Kuiper Belt until the 1990s when powerful telescopes began tracking faint KBOs (Kuiper Belt Objects) through the sky. This was a breakthrough because if you want to understand how a solar system forms (including alien solar systems) you need understand the stuff hiding out in the Kuiper Belt. Why? Because it’s pristine OG planetary material. It’s the material we all came from.

What this says with Pluto.

Ever wonder why, moving outwards from the Sun, you have the relatively small rocky planets, then the big giant planets and then really teeny-tiny Pluto (Pluto is smaller than our Moon). The answer is simple.

Pluto is not a planet it’s a Kuiper Belt Object!

It’s just one of those pieces of stuff left over from when the solar system was born. There are a few other bodies the size of Pluto out there in the Kuiper Belt so it’s not even that special.

OK, it is special but only because all the KBO’s are special. To know how planetary systems are created - including those that might harbor alien life - then we have to use the clues hidden in KBOs.

That’s why no one needs to whine about Pluto. It wasn’t demoted at all. We astronomers weren’t dissing Pluto back in 2006 when we changed its designation. We were just trying to tell everyone “There’s whole lot more to the solar system than we thought and it begins with Pluto." So no more whining. Pluto’s fate is a cause to celebrate not cry. We know more about the solar system than we did before.