Category Archives: Planets

On the Subject of Pluto

I’ve blogged on this subject before.

I was watching a program on the Science Channel, Last Planet From Our Sun, which was discussing the pros and cons of why Pluto would or would not be a planet. The program opened with a rather bold series of statements from Dr. Neil Tyson, Director of the Hayden Planetarium.

It seems that much of this hoopla over the status of Pluto is just a tempest in a teapot, and will end up amounting to nothing. Dr. Tyson, and several of his colleagues, have been agitating since 1999 (Pluto’s Honor, Natural History magazine, February 1999) concerning the status of Pluto, and rightly questioning whether or not the oddities surrounding it should exclude it from being called a ‘planet’.

“I hope we find plenty of objects bigger than Pluto. If they’re made of ice, and they are out there beyond Neptune, they are Kuiper belt objects. Get over it.”
Dr. Neil Tyson

I’ve mentioned this before, the oddities surrounding Pluto have always made it not a planet in my own judgment. It wasn’t until this latest mini-tempest that I even realized there were others out there who shared my opinion; people who actually work in the field of astronomy, even. The need to re-classify Pluto as a Kuiper belt object (as Ceres was classified as an asteriod when the nature of the asteriod belt was discovered) has been a known issue since the mid 1990’s when dozens of objects were found orbiting out beyond Neptune. The issue came to a head with the discovery of Eris (previously referred to as Zena) in 2005, a body larger than Pluto, much farther from the sun, and well outside the plane of the ecliptic. So it was either consider all these ice bodies as ‘planets’, or come up with a definition of planet that excluded them. Personally I’m beginning to agree with Dr. Tyson, the word planet is misleading, and covers an over-large range of bodies in the solar system.

The long and the short of it, though, is that anyone who was blindsided by the demotion of Pluto really wasn’t paying attention to astronomy news. It was only in the pipe for ten years before it happened…

And Then There Were Eight

After the last Blog entry on the subject of planets, I got quite a bit of feedback on my opinion; most of it negative. How to define what a planet was, based on conformance to the ecliptic plane, or on any determination other than ’roundness’ turned out to be more problematic than I at first thought. I finally came to the conclusion that what was needed was a distinction between belt objects that were round (I suggested the name ‘planetoid’ several times) and planets, rather than the other way around.

This is a lot like trying to define the word table, and coming up with a definition that fits what most people think of when they hear the word ‘table’. When I think planet, I can see virtually airless Mercury with no satellites on one end of the scale, and Jupiter the gas giant with it’s many moons on the other end. But what do they all have in common other than roundness? Gravitational dominance of their region of space, that is the other property that makes them planets. It’s what originally disqualified Ceres and her sisters in the asteroid belt. It’s why Pluto isn’t a planet way out in the Kuiper belt. The objects trapped in the Lagrange points defined by the planets just confirms this.

Imagine my surprise when I heard the news from the IAU. Pluto is no longer a planet, and the qualification for the IAU to consider a round stellar object a planet is that it must have “cleared it’s neighborhood”. I don’t care much for the wording used, but it seems to communicate the intent reasonably well. I’m on the winning side, for once.

Which makes me uneasy. I generally adhere to the observation “If you find yourself holding a majority opinion, check your assumptions”. Majorities are very rarely right, contrary to popular opinion. I was a little mollified when I discovered that the voting was limited to 424 out of a possible 10,000 members, so the majority that carried the vote is anything but. Still, it’s no different than the average city council race where more than half the population doesn’t even know it’s election day, much less bothers to vote. They still call it a win, why shouldn’t I?

Does any of this have any effect on the newly dubbed dwarf planet Pluto? No, it’s still spinning out in space, with it’s (at last count) three satellites. You wouldn’t think so to hear some of the arguments coming from the dissenters to the decision. Words like ‘farce‘. Why shouldn’t a professional community be allowed to determine the definitions for the words that they will use within their profession? Definitions in common use will remain calmly oblivious to whatever the ultimate outcome of the current astronomical dust-up is. The same majority usage that assigns definitions to words like ‘table’ will dominate the literary landscape, no matter what those of higher learning would prefer in the end.

Here’s hoping that some future child peering out a porthole in his parents’ family owned business/home (which also happens to be a spacecraft) will learn the correct usage of the word from a more knowledgeable parent.

“Hey, dad! Is that the planet Ceres?”

“Sorry son, Ceres isn’t really a planet. That’s why we have to dodge all these other rocks out here…”

So, How Many Planets are There, Anyway?

I started this entry several months ago, when the latest planet-sized object beyond Pluto’s orbit was located. At that time the astronomers were hemming and hawing over whether they were going to call it a planet; but since they called Pluto a planet, they pretty much had to call this discovery a planet as well. I’ve been waiting for the other shoe to drop. It appears that event has now taken place.

‘The other shoe’ is the IAU definition of ‘planet’. They recently formed a committee to come up with a definition that could be applied to all solar systems, and now they are floating that definition amongst their peers, looking for acceptance.

This new definition would yield 12 planets for this solar system, based on current knowledge. Some astronomers think this number could go as high as 24.

Personally, I think the astronomers are missing a key point in defining what is or isn’t a planet. Anyone who looks at the orbit of Pluto (or the Plutons, as the new definition refers to them) and contrasts it with the orbits of the ‘classical’ 8 inner planets, can probably get the point I’m trying to make here. Pluto is clearly not of the same nature as the rest of the planets. It’s orbit describes a body that is more akin to a comet than to a planet. The definition of planet should reflect this.

A planet should first and foremost be formed from the original accretion disk of the star that it orbits, or follow the same orbital pathway that the star’s gravity and spin dictates. Anything of planet size that doesn’t conform to this plane should be referred to as a ‘planetoid‘; of planet size, but not truly a planet.

Of course, this kind of level-headed thinking on the subject would yield no new planets for current and future astronomers to hang their names on, so I’m not looking for any of them to notice the argument at all, human nature being what it is.

Call me old fashioned, but I really think these types of defining moments should reflect the need for clarity, not the desire for self-aggrandizement.