A Diminished World

[woodwardiocom]

-We live in a solar system with eight planets.

-As of today, the International Astronomical Union's definition of "planet" is "A celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a . . . nearly round shape, and has cleared the neighborhood around its orbit." Pluto fails this definition in the last term.

-The IAU had been considering an alternate definition, which would have kept Pluto as a planet, and also added Ceres, Charon, and 2003 UB₃₁₃. We would then have been able to claim 12 planets (so far) in our solar system.

-I cannot help but feel we have lost something with this decision. Our exploration of our system and universe has forever turned up new strangeness, new things that don't fit our understanding or expectations, from the dancing moons of Jupiter, to the spokes in Saturn's rings, to the hot gas giants of nearby stars. We are forever going to discover new phenomena we will have to fit into our world. We can choose to let our definition of "planet" expand, to grow to embrace the strange, the new, the weird. Or, we can shunt these worlds into under-categories, to mark them as something less, something not as worthy. I think that by drawing back our skirts and rejecting the odd, we are turning away from the very purpose of exploration and discovery: Joining with the possibilities of the universe.

Comments

[beowabbit]

Personally, I liked the old definition of a planet, which was more or less any distinguishable discrete object that wasn’t a star. I mean, it doesn’t make a whole lot of sense to me to try to draw an arbitrary dividing line between small rocky or icy planets and large asteroids, or between icy planets and KBOs, or between KBOs and comets, and the same people who want to study comets are going to want to study some of the satellites of the gas giants, and the same people who study asteroids are going to want to study Phobos and Deimos, and the same people who want to study Mars and Mercury are going to at least want to take a look at Earth's Moon. And people studying climate on Earth and Venus are going to be fascinated by Titan, and people studying geology on Earth and Venus are going to be fascinated by Io.

I mean, it’s all semantics, so I guess the words don’t matter that much, but any dividing line that includes Mercury is going to be very arbitrary, and any dividing line that includes Earth is going to be pretty arbitrary. (You could make a case that the solar system has four planets and some rubble. You could probably make a case that the solar system has six or seven planets and some rubble, but it would be a harder case.)

I have to say, I was kind of looking forward to Ceres, Pallas, Vesto, Charon, Xena, and Quaoar being talked about as planets. Oh, well, they aren’t any less interesting for not being called planets.

(And it would have seemed a bit strange to call Pluto/Charon a double planet system, and not Earth/Moon; yeah, the center of gravity of the Earth/Moon system is inside Earth, but only just.)

[katkt.livejournal.com]

You could make a case that the solar system has four planets and some rubble.

An aside:
I'm re-reading Stranger in a Strange Land (it's been a while), and he makes exactly that point in a little half-sentece aside.

[beowabbit]

s/Vesto/Vesta/

Or maybe s/Vesto/Vespa/, and we can scoot around the Solar System on it waving and saying “Ciao!”

[futurenurselady.livejournal.com]

One thing this decision and the news reports leading up to it have shown me is the gross miconceptions laymen have about the solar system and our galaxy.

In one report, an anchorwoman called our solar system "the Milky Way." That's the name of our galaxy, not our solar system.

In a televised opinion piece, a news correspondent questioned the importance of the definition of a planet.

[whswhs.livejournal.com]

By that definition of planet, I think a case could be made that Earth is not a planet. After all, the Moon is a pretty substantial body for Earth to have failed to "clear."

[woodwardiocom.livejournal.com]

-Yeah, I'm a little fuzzy on what they mean by "clear", too. Pluto has failed to "clear" because its orbit crosses Neptune, but then why does Neptune qualify?

[beowabbit]

-Yeah, I'm a little fuzzy on what they mean by "clear", too. Pluto has failed to "clear" because its orbit crosses Neptune, but then why does Neptune qualify?

Because Pluto is in a 2:3 orbital resonance with it, so while Pluto crosses Neptune’s orbit, it never crosses it when Neptune is nearby. If Pluto’s orbit weren’t exactly in synch with Neptune’s, Neptune would have ejected it from its orbit — either into a more distant orbit, or to become one hell of a comet. So Neptune’s gravitational force limits (and probably had a hand in creating, if I’m remembering correctly) Pluto’s current orbit.

There are small bodies that cross the orbits of other planets (definitely Jupiter and Earth that I know of, perhaps others) that are in similar resonances.

[beowabbit]

Oh, and I think another part of the issue is that there are various other bodies that Pluto’s orbit crosses or approaches, and Pluto isn’t big enough to have disturbed them. (Some of them are also plutinos like Pluto, i.e. in a 2:3 orbital resonance with Neptune.)

[be-well-lowell.livejournal.com]

But the Earth did "clear" the Moon. The Moon orbits the Earth, not the Sun.

[badseed1980.livejournal.com]

A question: Why is a non-planet celestial body "not as worthy?" Why not just "something different?"

[woodwardiocom.livejournal.com]

-Speaking of heavenly bodies . . .

-For me, the difference between "planet" and "dwarf planet" feels like the difference between "bus" and "short bus"; "tennis" and "table tennis"; "movie" and "home movie".

[buxom-bey.livejournal.com]

I wonder if we should hold a wake?

[katkt.livejournal.com]

I think you're looking at things from the wrong perspective. This doesn't reject Pluto or turn it away, it highlights the fact that Pluto is a new thing and encourages efforts to understand it and find other, similar things. Pluto isn't the object it was thought to be 30 years ago.

I trust the scientistific judgement of the IAU that it is scientifically informative to have these different classes. Personally, I would have been inclined to make a seperate class for the gas giants as well, and maybe to disqualify Mercury, but I'm not an astronomer.

"Dwarf" seems a little disparaging, but upon reflection it's a fairly neat summary of the distinction that's being made.

[bluepapercup]

I have to disagree.

It makes perfect sense to me - that is, as we understand the univere better, we clarify MORE, not less. When definitions are too broad, they cease to be useful, because they mean too many things.

It seems logical and natural to me to have it ordered the new way. Four inner rocky planets, four outer gasseous planets, and the new class of trans-Neptunian rocky objects.

It's all a lot of fun until some horked-off Plutonian decides to destroy the earth.

[spacecrime.livejournal.com]

"Excuse me while I reclassify your planet . . . with my Illudium Q-36 Explosive Space Modulator!"

-- Chris

[superfinemind.livejournal.com]

...Sucking up a moon when it's only however big ought to count as clearing. I mean, Luna's bigger than Pluto and doesn't have any natural orbiting bodies.

And, I love the way you write. ^_^

[woodwardiocom.livejournal.com]

Sucking up a moon when it's only however big ought to count as clearing.

-Heck, three moons, at last report. (Though, frankly, the more I learn about Pluto, the more I suspect alien involvement.)

And, I love the way you write.

[smile] Thank you.