What About Pluto, Dad?

Every family has a sentence that teaches kids about the planets. Ours comes from There’s No Place Like Space! All About Our Solar System from The Cat in the Hat’s Learning Library. It’s a memory trick built around money:

Mallory Valerie Emily Mickels just saved up nine hundred ninety-nine nickels.

The first letter of each word stands for a planet — Mercury, Venus, Earth, and so on down to Neptune. The nickels are just how the sentence ends.

My daughter’s name is Emily. She figured out a long time ago that the third word in the rhyme is Emily. Earth is the third planet, and that’s where she lives, so the logic was obvious to her: Earth is Emily’s planet. Once she decided that, the rest of the solar system became her business too.

When we get to the rhyme on page 26, she asks the same thing every night:

“What about Pluto, Dad?”

Then she fixes it herself.

The rhyme ends with the nickels. Emily adds one more coin, a smaller one.

“And pennies.”

Pennies for Pluto.

I don’t correct her. I’ve been thinking about this longer than I’d like to admit — one bedtime at a time.

Nothing about Pluto changed

What always bothered me is that Pluto itself never changed.

It didn’t shrink. It didn’t move. It didn’t suddenly become less interesting.

What changed was a definition.

In 2006, the International Astronomical Union wrote down, for the first time, an official meaning for the word planet. To qualify, an object had to orbit the Sun, be massive enough for its gravity to pull it into a roughly round shape, and have “cleared the neighborhood” around its orbit.

Pluto passes the first two without any trouble.

The third is where it loses its place on the list.

Pluto lives in the Kuiper Belt, a huge region beyond Neptune filled with icy bodies. It shares that part of the solar system with thousands of other objects. Under the new definition, that makes it a dwarf planet.

Just like that, the solar system dropped from nine planets to eight.

The astronomers had a point

I don’t think the people who voted for the change were being unreasonable.

A year earlier, astronomers had discovered Eris, another icy world beyond Neptune that turned out to be more massive than Pluto. If Pluto was a planet, then Eris probably had to be one too.

And Eris wasn’t alone.

Sedna, Haumea and Makemake all turned up in the same few years. The neat list every kid memorized suddenly looked a lot less neat.

I understand why the IAU wanted a line.

Here’s where they lose me

The problem is that the line seems to describe Pluto’s address more than Pluto itself.

If you could somehow pick up Earth and move it into the Kuiper Belt, Earth wouldn’t clear that enormous region either. It would still be Earth. Nobody would argue otherwise.

That’s why I’ve always found the third rule a little unsatisfying. It tells us something about Pluto’s surroundings, but not necessarily about Pluto.

I’m hardly the first person to think that way. Alan Stern, who led NASA’s New Horizons mission, has argued for years that a planet should be defined by what it is, not by what’s nearby.

And it’s not just scientists.

In 2019, then-NASA Administrator Jim Bridenstine said, “In my view, Pluto is a planet.” He explained that it was how he learned it as a kid, and he wasn’t changing his mind.

That comment stuck with me because it gets at what makes Pluto different from every other classification debate in astronomy.

Twenty years later, people are still bringing their childhood solar system into the argument.

Then we finally saw it

For most of my life, Pluto was a planet with no face.

We had artist’s impressions and textbook drawings, but nobody actually knew what the surface looked like.

Then, on July 14, 2015, NASA’s New Horizons spacecraft flew past Pluto and changed that forever.

The mission carried a small amount of Clyde Tombaugh’s ashes — the man who discovered Pluto in 1930. After a journey of nearly ten years, the spacecraft turned Pluto from an idea into a place.

And what a place.

The first images showed a world with mountains made of water ice, a thin blue atmosphere, and the now-famous heart — the left half of it a frozen nitrogen plain called Sputnik Planitia, still slowly churning like a glacier.

Pluto has five moons. The largest, Charon, is so big compared to Pluto that the two worlds orbit a point in space between them rather than inside either body. Scientists also think a liquid ocean may still exist beneath Pluto’s icy crust.

Whatever you want to call that world, it doesn’t feel like an afterthought.

Even the book changed

The strangest part of this whole thing turned up when I looked closer at Emily’s book.

Her copy is the revised edition. The copyright page lists both 1999 and 2009 and notes that it was “originally published in a different form.”

That made me curious.

So I tracked down the earlier version.

The 1999 book used a different rhyme:

Mallory Valerie Emily Meetzahs just served us nine hundred ninety-nine pizzas!

The last word — pizzas — stood for Pluto.

On the facing page, there was even a giant stack of pizzas celebrating the ninth planet.

By 2009, Pluto was gone from the rhyme.

Meetzahs just served us… pizzas became Mickels just saved up… nickels.

A pizza dinner for nine turned into spare change for eight.

The tower of pizzas disappeared too.

For some reason, that hit me harder than the actual vote.

A decision made by astronomers in Prague had worked its way into a children’s rhyme.

Emily, for the record, remains completely unconvinced.

Every night she puts Pluto back.

Pennies for Pluto

So is Pluto a planet?

Officially, no.

The IAU definition is the accepted one, and under that definition Pluto is a dwarf planet.

I understand the reasoning.

But maybe I’m biased.

I grew up with nine planets and never saw a compelling reason to stop thinking of Pluto as one.

The part I didn’t expect is Emily.

She was born into an eight-planet solar system. Her own book was rewritten to leave Pluto out. She has no official reason to care about it at all.

Yet she cares more than I do.

She knows Pluto because I know Pluto. Because her grandmother knows Pluto. Because there is an Illustrated Atlas of the Universe on our coffee table, published in 2006, just months before the vote, that we have looked at together.

That atlas hedges, right in its first line. “The last planet in the Solar System,” it says, “if you choose to call it a planet.” Then it makes a prediction: if Pluto had been discovered in the last decade it would count as the largest object in the Kuiper Belt, but for historical reasons it will probably keep the status of planet.

It was wrong inside a year.

Pluto didn’t survive in her edition of the book.

It survived in the people reading it.

If they hadn’t demoted Pluto, I don’t know if we’d still be talking about it twenty years later.

Most people can’t name another dwarf planet.

Almost everyone can name the one that got kicked out.

Maybe that’s why the argument never goes away. The definition changed. Pluto didn’t. It’s still sitting in old atlases, old textbooks, classroom posters, and apparently in the head of a kid who wasn’t even born when the vote happened.

At our house, the correction always arrives at the same spot.

We get to the nickels, and then, from somewhere near the pillow:

“And pennies.”

For Pluto.

If you want the whole story of that flyby — the decades it took to get New Horizons funded, built and flown — it is told firsthand in Chasing New Horizons, by Alan Stern, the mission’s own leader. And the book this essay is about is our pick for ages 4–7 in the best space books for kids. The atlas quoted above is still in print in its 2006 hardcover.

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