One Astronomer's Quest To Reinstate Pluto As a Planet

sarahnaomi writes: Most of us grew up believing that tiny, distant Pluto was the outermost planet in our solar system. Then, one day, the scientific powers that be decreed that it wasn't. But it seems the matter is far from settled. David Weintraub—who describes Pluto's exile as a stunt organized by a "very small clique of Pluto-haters"—would have the dwarf world rejoin the ranks of our Solar System's fully-fledged planets today. But solid evidence that Pluto deserves the title may come in July, when NASA's New Horizons spacecraft slingshots around the icy rock and sends us back a detailed picture of its composition. Pluto's planethood was revoked by majority vote on the final day of the 2006 IAU conference. Over 2,500 astronomers attended the meeting throughout the week, but only 394 votes ultimately decided Pluto's fate: 237 in favor of demoting the planet and 157 against.

Comments

Better definition of planet

[Hanzie]

As far as I'm concerned, if it's gravitation is enough to pull it into a sphere, it's a planet. Yes, I'm happy counting Luna and a bunch of other satellites. Let's face it, "Believing" has nothing to do with it. We grew up "choosing to label" Pluto as a planet.

How many exoplanets pass the current IAU definition of 'planet'? I bet a bunch don't.

Re:Better definition of planet

[ideonexus]

Up until last Thursday night, I completely agreed with you. I thought that if an object had enough mass to pull itself into a sphere, it should be a planet. I thought the IAU's definition of planet was an offense to reason--well, I still think it is. Requiring an object to have "cleared its orbit" is a silly concept that would mean gas giants larger than Jupiter would be "Dwarf Planets" if they were found in a proto-planetary disc. The name, "Dwarf Planet," is completely stupid and offensive. How is a "Dwarf Planet" not a planet if it has "Planet" in the #$%^ing name???

Then, just this last Thursday night, I attended a lecture by the very engaging, highly-studied Neil deGrasse Tyson. The guy who declassified Pluto as a planet in the Hayden Planetarium exhibits long before the IAU did so officially. He explained to us that Pluto was mostly a dirty ball of ice... like a comet. In fact, if it were in orbit around the Earth, it would have a tail.

That took me aback. If Pluto is just a particularly large Kuiper Belt object--if Pluto is just a large comet that isn't close enough to the Sun to melt, then I must admit that it doesn't make sense to call it a planet.

This is a bit of an iconoclasm for me, so I'm still figuring out my position on the matter, but I'm leaning toward accepting that Pluto is not a planet, but that the IAU is a bunch of numbskulls who need to fix their illogical, nonsensical definition of "Planet" and take the word "Planet" out of their labels for things that aren't planets. This is the kind of political bullcrap that turns kids off to science.

Of course, all this could change when New Horizons reaches Pluto this July.

Re:What's the big deal, anyway?

[confused one]

That's the general idea. You have to add all the objects that meet the criteria. The current criteria does not depend on characteristics of the object itself; the definition includes characteristics of the surrounding objects as well. I tend to agree with the argument that the current definition is wrong, for this reason.

The Kuiper belt and scattered disk are where all the remaining stuff left over from the formation of the solar system ended up. It was pushed out there by the larger planets. Unless the body is very large, for example like Uranus, it's not going to be able to "clear it's orbit" in that region of the solar system. If another large planet did exist out there, it would probably scatter everything in it's orbit, effectively pushing the Kuiper belt and scattered disk further out. Any smaller body, perhaps even an Earth sized body, would be unable to clear it's orbit. So, if the Earth's double was found out there, you would have to call it a "dwarf planet" by the current definition. That doesn't make sense.

Re:And still

[mister_playboy]

Really, the only categorization issue that I'm adamant about is that Pluto-Charon is called a binary. The Pluto-Charon barycentre is not inside Pluto, therefore Charon is not rotating around Pluto, the two are corotating around a common point of space between them. That's a binary.

The barycenter of the Sun-Jupiter system lies at 1.068 solar radii, outside the Sun. Do you think they should be called a binary?

Re:And still

[Anonymous Coward]

"Planet" originally meant a star which moved through the constellations. The concept of size or distance or mass was utterly irrelevant. Having "categories" of planets, particularly given that there were less than a dozen examples, was a ludicrious suggestion.

It still is. There are still less than a dozen planets that can even be halfway considered observed to the point of resolved, much less understood. The idea that humans have somehow categorised these objects is as absurd as it is untenable.

There is no definition of a planet. And, given the people currently in charge of the study of them, there probably never will be.

Re:And still

[mister_playboy]

Jupiter emits more heat into space than it receives from the Sun.

(I agree with you, just playing devil's advocate).