Pluto IS a planet; debate isn't overlaureleJanuary 22 2010, 00:22:12 UTC
Planet Pluto has not "fallen," and the IAU was never "forced" to define the term planet, an act many members now regret. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. One reason the IAU definition makes no sense is it says dwarf planets are not planets at all! That is like saying a grizzly bear is not a bear, and it is inconsistent with the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto’s orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another is essentially useless. Pluto is a planet because it is spherical, meaning it is large enough to be pulled into a round shape by its own gravity--a state known as hydrostatic equilibrium and characteristic of planets, not of shapeless asteroids held together by chemical bonds. These reasons are why many astronomers, lay people, and educators are either ignoring the demotion entirely or working to get it overturned. The requirement that an object must "clear its orbit" to be a planet was concocted specifically to exclude Pluto, and there is no reason for it.
This isn't about resistance to change; it's about resistance to bad change. Not all change is good. In this case, the IAU decision went in the wrong direction, narrowing rather than broadening the definition of planet even while we are discovering more and more diverse planets in this and other solar systems.
Pluto actually has a lot in common with the other eight planets. In fact, it could be said to have more in common with Earth than Jupiter does. Pluto and Earth both have solid surfaces, are geologically differentiated into core, mantle, and crust, have weather, and have a large moon formed from an impact. Unlike asteroids and shapeless Kuiper Belt Objects, Pluto, Haumea, Makemake, Eris, and Ceres all are shaped by gravity--a characteristic of planets.
For the other side of this very much ongoing debate, check out "The Case for Pluto" by Alan Boyle, "Is Pluto A Planet?" by Dr. David Weintraub, transcripts of the Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in August 2008 in response to the IAU decision (transcripts are here: http://gpd.jhuapl.edu/ and my Pluto Blog at http://laurele.livejournal.com
In spite of what the IAU claims, dwarf planets should simply be considered a third class of planets, in addition to terrestrials and jovians. They are planets because they are in hydrostatic equilibrium but of the dwarf subclass because they do not gravitationally dominate their orbits. Using this definition, we have 13 planets and counting: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.
Re: Pluto IS a planet; debate isn't overmshadesJanuary 22 2010, 01:33:36 UTC
You're right - the debate isn't over. When New Horizons gets out there in a few years, the data it collects about Pluto and its environs will no doubt reignite the conversation, and I look forward to it.
Here's my thought, though: Taxonomy relies on similarities. Of the thirteen major spherical objects orbiting the sun, eight of them share the similar feature of having cleared out their orbits. Four do not. Therefore, to use the same label for those four as the other eight is sloppy classification. There is nothing wrong with re-classifying objects that share similarities if that makes it easier to understand how the solar system works.
If you re-read Tyson's book, you'll see that there are many points where he notes that the classical understanding of the Solar System is outdated, and the objects it inhabits can be classified and reclassified any number of ways. The Rose Center exhibition was not a vendetta against Pluto - it was an attempt to group together things that are similar, and Pluto shares characteristics with Kuiper Belt objects that none of the eight planets do. Therefore, putting it with those Kuiper Belt objects made sense.
A note about your "four percent of the IAU" comment: Tyson was correct in noting that any good statistician or pollster would sell his or her grandmother to be able to poll four percent of any population. That would be like gauging American public opinion by polling 12,000,000 people, when most national opinion polls top out at a couple thousand. So to say it's "only" four percent is to grossly underestimate how accurate the vote probably was.
Besides, of that "only" four percent, 90% of them voted for the new definition of what a planet is. Assuming that's a random sample of astrophysicists (and you're right - they were not "forced" to do this - it was undertaken of their own free will), he says, the margin of error on that poll is about 3% - not even close to being a controversy, statistically speaking.
One last thing, and then I really have to get ready for work. You refer to "13 planets and counting." When will you stop counting? If we find another five or ten or fifty spherical objects in the Kuiper Belt, how many will it take before you finally consent to re-classifying the sol-orbiting bodies of the system, and will you continue to insist that Pluto be granted special status?
I have a special place in my heart for Pluto, too. But science cannot be governed by sentimentality. Reclassifying Pluto doesn't mean it's kicked out of the club, or that no one cares about it anymore. It's simply a new way of understanding a solar system that is vastly more complex than we knew back when Tombaugh found that contentious little sphere.....
Re: Pluto IS a planet; debate isn't overlaureleJanuary 22 2010, 02:42:02 UTC
First, the argument that it is only sentimentality supporting Pluto remaining a planet is a straw man. Those who seek to keep the number of planets low simply for convenience or memorization can be equally accused of being motivated by sentimental reasons.
My answer is, we never stop counting. So what if our solar system ends up with several hundred planets? If that is what it has, then that is what it has. Memorization is really not important. Understanding concepts is. Once upon a time, we knew little more than the names of the planets. Today, we know the solar system as a complicated and very diverse entity. No one is asked to memorize the names of Jupiter's 63 moons, yet at the same time, no one says, keep the number of Jupiter's moons at four because 63 are too many to memorize. Kids aren't taught to memorize all the rivers or mountains in the world. The Periodic Table of the Elements is not kept to a small amount just to make memorization easier. The real paradigm shift to which we need to adjust is not from 9 to 8 planets but from 9 to potentially hundreds, in this and other solar systems.
The fact that only four percent of the IAU voted is problematic for several reasons. First, the IAU allows no absentee voting. This vote was held on the last day of a two-week conference. Most of the 2,500 attendees had already left, expecting a different resolution to be put on the floor of the General Assembly. At the last minute, a very specific--and biased--group of astronomers rushed through an alternate resolution, violating the IAU's own bylaws, which state that resolutions must first be vetted by the appropriate committee before being brought to the full General Assembly. If you watch the proceedings, it is clear the 424 who remained--mostly those in on this alternate resolution--themselves were clearly confused about the text of a resolution they first saw the morning of the vote.
This four percent was heavily dominated by one camp in the planet debate--the dynamicists. They focus on the way objects interact with one another and therefore believe that only those objects large enough to gravitationally dominate their orbits should be planets. In contrast, geophysicists or planetary scientists, focus on the objects themselves, their composition and individual characteristics. Both are legitimate ways of viewing the solar system. However, planetary scientists were seriously under-represented in this vote. Most IAU members are not planetary scientists but other types of astronomers. And many planetary scientists are not IAU members and therefore had no say in this at all.
I don't think it's problematic to use the same label for the five objects that do not gravitationally dominate their orbits as for the eight that do provided this distinction is made clear through the use of subcategories. Dwarf planets should simply be a subclass of planets that do not dominate their orbits. These objects still do have a lot more in common with the big planets than with the asteroids in that they have geology and weather and are shaped by their own gravity. One could equally say it is problematic to class Earth and Jupiter in the same category. Jupiter's composition is similar to that of the sun; it has what amounts to a "mini-solar system" of 63 moons and no solid surface. But here again, the solution is to separate them into subclasses of planets. Earth is a terrestrial planet, and Jupiter is a gas giant or jovian planet. Those who want to exclude spherical objects just because they do not gravitationally dominate their orbits do not seem to get that we can have more than two subclasses of planets.
Pluto, Haumea, Makemake, and Eris should be dually classified as both planets and Kuiper Belt Objects. This takes into account both where and what they are. One does not preclude the other.
I don't blame Tyson for anything; in fact, he himself makes it clear he is not happy with the IAU decision. And I still urge you to read Boyle's book just to get a better discussion than I can provide of the other side of this issue.
This isn't about resistance to change; it's about resistance to bad change. Not all change is good. In this case, the IAU decision went in the wrong direction, narrowing rather than broadening the definition of planet even while we are discovering more and more diverse planets in this and other solar systems.
Pluto actually has a lot in common with the other eight planets. In fact, it could be said to have more in common with Earth than Jupiter does. Pluto and Earth both have solid surfaces, are geologically differentiated into core, mantle, and crust, have weather, and have a large moon formed from an impact. Unlike asteroids and shapeless Kuiper Belt Objects, Pluto, Haumea, Makemake, Eris, and Ceres all are shaped by gravity--a characteristic of planets.
For the other side of this very much ongoing debate, check out "The Case for Pluto" by Alan Boyle, "Is Pluto A Planet?" by Dr. David Weintraub, transcripts of the Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in August 2008 in response to the IAU decision (transcripts are here: http://gpd.jhuapl.edu/ and my Pluto Blog at http://laurele.livejournal.com
In spite of what the IAU claims, dwarf planets should simply be considered a third class of planets, in addition to terrestrials and jovians. They are planets because they are in hydrostatic equilibrium but of the dwarf subclass because they do not gravitationally dominate their orbits. Using this definition, we have 13 planets and counting: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.
Reply
Here's my thought, though: Taxonomy relies on similarities. Of the thirteen major spherical objects orbiting the sun, eight of them share the similar feature of having cleared out their orbits. Four do not. Therefore, to use the same label for those four as the other eight is sloppy classification. There is nothing wrong with re-classifying objects that share similarities if that makes it easier to understand how the solar system works.
If you re-read Tyson's book, you'll see that there are many points where he notes that the classical understanding of the Solar System is outdated, and the objects it inhabits can be classified and reclassified any number of ways. The Rose Center exhibition was not a vendetta against Pluto - it was an attempt to group together things that are similar, and Pluto shares characteristics with Kuiper Belt objects that none of the eight planets do. Therefore, putting it with those Kuiper Belt objects made sense.
A note about your "four percent of the IAU" comment: Tyson was correct in noting that any good statistician or pollster would sell his or her grandmother to be able to poll four percent of any population. That would be like gauging American public opinion by polling 12,000,000 people, when most national opinion polls top out at a couple thousand. So to say it's "only" four percent is to grossly underestimate how accurate the vote probably was.
Besides, of that "only" four percent, 90% of them voted for the new definition of what a planet is. Assuming that's a random sample of astrophysicists (and you're right - they were not "forced" to do this - it was undertaken of their own free will), he says, the margin of error on that poll is about 3% - not even close to being a controversy, statistically speaking.
One last thing, and then I really have to get ready for work. You refer to "13 planets and counting." When will you stop counting? If we find another five or ten or fifty spherical objects in the Kuiper Belt, how many will it take before you finally consent to re-classifying the sol-orbiting bodies of the system, and will you continue to insist that Pluto be granted special status?
I have a special place in my heart for Pluto, too. But science cannot be governed by sentimentality. Reclassifying Pluto doesn't mean it's kicked out of the club, or that no one cares about it anymore. It's simply a new way of understanding a solar system that is vastly more complex than we knew back when Tombaugh found that contentious little sphere.....
Reply
My answer is, we never stop counting. So what if our solar system ends up with several hundred planets? If that is what it has, then that is what it has. Memorization is really not important. Understanding concepts is. Once upon a time, we knew little more than the names of the planets. Today, we know the solar system as a complicated and very diverse entity. No one is asked to memorize the names of Jupiter's 63 moons, yet at the same time, no one says, keep the number of Jupiter's moons at four because 63 are too many to memorize. Kids aren't taught to memorize all the rivers or mountains in the world. The Periodic Table of the Elements is not kept to a small amount just to make memorization easier. The real paradigm shift to which we need to adjust is not from 9 to 8 planets but from 9 to potentially hundreds, in this and other solar systems.
The fact that only four percent of the IAU voted is problematic for several reasons. First, the IAU allows no absentee voting. This vote was held on the last day of a two-week conference. Most of the 2,500 attendees had already left, expecting a different resolution to be put on the floor of the General Assembly. At the last minute, a very specific--and biased--group of astronomers rushed through an alternate resolution, violating the IAU's own bylaws, which state that resolutions must first be vetted by the appropriate committee before being brought to the full General Assembly. If you watch the proceedings, it is clear the 424 who remained--mostly those in on this alternate resolution--themselves were clearly confused about the text of a resolution they first saw the morning of the vote.
This four percent was heavily dominated by one camp in the planet debate--the dynamicists. They focus on the way objects interact with one another and therefore believe that only those objects large enough to gravitationally dominate their orbits should be planets. In contrast, geophysicists or planetary scientists, focus on the objects themselves, their composition and individual characteristics. Both are legitimate ways of viewing the solar system. However, planetary scientists were seriously under-represented in this vote. Most IAU members are not planetary scientists but other types of astronomers. And many planetary scientists are not IAU members and therefore had no say in this at all.
I don't think it's problematic to use the same label for the five objects that do not gravitationally dominate their orbits as for the eight that do provided this distinction is made clear through the use of subcategories. Dwarf planets should simply be a subclass of planets that do not dominate their orbits. These objects still do have a lot more in common with the big planets than with the asteroids in that they have geology and weather and are shaped by their own gravity. One could equally say it is problematic to class Earth and Jupiter in the same category. Jupiter's composition is similar to that of the sun; it has what amounts to a "mini-solar system" of 63 moons and no solid surface. But here again, the solution is to separate them into subclasses of planets. Earth is a terrestrial planet, and Jupiter is a gas giant or jovian planet. Those who want to exclude spherical objects just because they do not gravitationally dominate their orbits do not seem to get that we can have more than two subclasses of planets.
Pluto, Haumea, Makemake, and Eris should be dually classified as both planets and Kuiper Belt Objects. This takes into account both where and what they are. One does not preclude the other.
I don't blame Tyson for anything; in fact, he himself makes it clear he is not happy with the IAU decision. And I still urge you to read Boyle's book just to get a better discussion than I can provide of the other side of this issue.
Reply
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