Pluto, again
Nova had The Pluto Files on, with Neil deGrasse Tyson defending the de-planetization of Pluto. He's professing to not quite understand why people are fond of Pluto.
Personally, I'm not particularly fond of it, but I do think that if it's round, orbits the sun, and has its own moons, how can it not be a planet? But then, nobody asked me...
(Of course, there are bigger things than Pluto out there, like Eris, but I don't quite see why we can't have lots of planets. That's a goofy reason. Of course, on the other hand, I do see the "clearing space" argument, too... )
Labels: astronomy, entertainment
7 Comments:
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At 9:49 PM, March 05, 2010
Laurel Kornfeld had this to say...
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At 8:19 AM, March 06, 2010
The Ridger, FCD had this to say...
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At 7:19 AM, March 08, 2010
Anonymous had this to say...
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At 4:14 PM, March 08, 2010
Barry Leiba had this to say...
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At 6:38 PM, March 08, 2010
The Ridger, FCD had this to say...
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At 3:01 PM, May 12, 2010
The Ridger, FCD had this to say...
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At 3:10 PM, May 12, 2010
Laurel Kornfeld had this to say...
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<-- Older Post ^ Home Newer Post -->Of course we can have lots of planets. The real problem here is that some people cannot deal with the paradigm shift from a solar system with 9 planets to one with potentially hundreds.
You have every right to have a say in this, as does everyone. Who said four percent of the IAU could concoct a confusing, unusable planet definition and then compel the world to use it? People care because they understand that it is problematic for a tiny group of people, in violation of their group's own bylaws, to establish a definition that has significant opposition within the astronomy community.
If an object is round, meaning it is large enough to be pulled into a round shape by its own gravity--a state known as hydrostatic equilibrium--and it orbits the Sun, it is a planet. As you can see, many astronomers support this alternative definition. Planets don't even have to have moons, as neither Mercury nor Venus have any.
Tyson seems to be slowly moving away from strong opposition to Pluto being classed as a planet to a position that is more neutral. That is to his credit.
Some of the arguments are just silly.
It's small!! (So's Mercury)
There would be too many!! (So we can't memorize them all. So what?)
Plus, as you say, Mercury and Venus don't have moons - and let's face it, Mars's moons are pretty substandard.
I blogged my own views on this back in 2006 - to summarise, I'm with the IAU in agreeing that Pluto is not a planet.
There's a clear dividing line between bodies that have cleared out their orbits (or, to use Mike Brown's superior wording, that dominate their orbits) and bodies that haven't. Any graph showing the properties of the relevant bodies will show an impressive gulf between the two. (Though not as impressive, of course, as the gulf between rocky planets and gas ones.) There is no known body occupying any sort of grey area.
There is no clear dividing line between bodies that are round and bodies that aren't, or between bodies that have moons and bodies that don't.
In my opinion, better to have a definition based on a division that actually exists in nature.
As for the paradigm shift that would be required if we accepted the notion that any spherical Kuiper Belt object is a planet, personally I think that accepting a much greater number of planets would be less of a shift than accepting the notion that they cannot in principle be listed in order of distance from the sun (not possible when you're dealing with highly elliptical orbits). But this isn't an argument pertaining to what the definition should be.
«There would be too many!! (So we can't memorize them all. So what?)»
Apart from the issue of whether we care to memorize them or not:
How many are we talking about? What are the limits to memorization?
Do you not have all the US states memorized? And the Canadian provinces as well? And the capitals of all of those?
I have a friend who has all 79 episode titles of the original Star Trek series memorized.
In order.
We're really able to memorize a lot of crap, when we put our minds to it.
@outerhoard: Sure, that's a reasonable definition. I don't disagree with that kind of reasoning. It's the other kind (either way) I can't stand.
(Actually, Barry, no. I don't have those things memorized (though I can come up with the states and provinces if I have to, after a while). )
There may be a clear dividing line between objects that do and do not gravitationally dominate their orbits, but that does not mean the latter are not planets. Dr. Alan Stern coined the term dwarf planet to indicate objects large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. However, he never intended for dwarf planets to not be considered planets at all. He did intend for dwarf planets to be a new subclass of planets in addition to terrestrials and jovians. This would be consistent with the use of the term "dwarf" in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies.
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