I’ve been listening to The Pluto Files by Neil DeGrasse Tyson, director of the Hayden Planetarium in New York City. In 2001 the Hayden Planetarium took a big hit for leaving Pluto out of some depictions of the Solar System in their new Rose Center for Earth and Space Science. Later, when the astronomical community at large revoked Pluto’s planethood, it seemed that maybe the Rose Center got it right in the first place.
Tyson shares his own views on why their treatment of Pluto was educationally sound, and I think he’s exactly right. Tyson makes the point that counting planets is a pointless exercise. Much more useful, sensible, and educational is to group bodies together to compare and contrast properties. The terrestrial planets form a group, the asteroids form a second, the gas giants a third, and the Kuiper belt objects, of which Pluto is one of the largest we know, form a fourth. It makes eminent sense, which is of course why it fell on completely deaf ears.
The letters that Tyson shares in the book are both hilarious and depressing. The passion that people express for keeping Pluto a planet reveal so much about how we think. Children can be excused, I suppose, for wanting to “stand up for the little guy.” But adults, one would think, should know better.
There’s a compelling argument to be made that at least the whole controversy got people thinking about the universe. But when I look at the conversation as it came out, I see a missed opportunity.
Instead of tossing out Pluto, which isn’t really what happened but is what came out, the thing to toss out was the word “planet.” It’s just as well to say “body” or “world”, and that can include just about everything, including the seven moons bigger than Pluto, including the asteroids smaller than Pluto. In fact, the idea of “planet” was always a shaky one.
Consider Jupiter as compared with Earth, for instance. The two have virtually nothing in common. Jupiter is 318 times as massive as Earth. (Earth, in case you’re wondering, is 455 times as massive as Pluto.) Yet Jupiter is less than one-quarter as dense as Earth. Jupiter whirls around its huge, spread-out mass in less than 10 hours. It is covered in hundreds of miles of hydrogen-rich clouds, over a liquid hydrogen layer that stretches for perhaps 12,000 miles. Consider that the deepest ocean spot on Earth is at best a few miles deep. Below the liquid hydrogen is a layer of metallic hydrogen, and finally at its core is the rock and iron that mark the only real similarity between the two worlds. Yet this core of metal and rock would hardly be recognizable, 14 or more times the size of Earth and under tremendous pressure. While the Earth has a single natural satellite, Jupiter at last count is up to 62 worlds in its complex system, not including its rings.
My point is, if we’d somehow evolved on a gas giant, we probably wouldn’t consider puny bits of rock like Earth as anything like real “planets.” The concept of planet itself is the problem, not the way we decide to count them.
So instead of throwing Pluto out, let’s throw them all out! I suggest entirely new names for these bodies – Jovians, Terrans, and debris. Our solar system contains, then, four Terrans, four Jovians, and lots and lots of debris.
Sorry, Pluto, but you’re debris. No offense.