The Debate So Far
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Point
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Counterpoint
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Pluto has an atmosphere
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Well, sometimes, but Mercury doesn't
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Pluto has a Moon
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So do several asteroids
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Pluto has a large Moon
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So do several Trans-Neptunians
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Pluto orbits the Sun
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So do all asteroids (except those captured by Mars or Jupiter), and like
Pluto, many of them cross the orbits of major planets
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Don't take anything away from Clyde Tombaugh
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Pluto's status (or lack thereof) has little to do with Clyde Tombaugh—it
is a very interesting object without regard for how it is classified
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Pluto was classified as a planet when it was discovered, and it should remain
that way
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Galaxies used to be called Extragalactic Nebulae too, at a time
when we (also) did not understand the realm we were naming/characterizing
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We shouldn't be debating this subject
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Is this about science or religion?
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We have had nine planets in textbooks for more than 70 years
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We had eleven planets in textbooks for more than 50 years in the first half
of the 19th century
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Levy, S&T Focal Point 8/1994: ... astronomers decided long ago to
classify objects as major planets, minor planets (asteroids), moons, and
comets.
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I see the same argument that Buie uses here. Yes, long ago, astronomers had
no idea that the tip of the iceberg was discovered when they found Pluto.
Both Ceres and Uranus, when first discovered, were thought to be comets.
Should we still call them the Ceres comet or Uranus comet?
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Levy, S&T Focal Point 8/1994: In the 64 years since, we have become
used to Pluto as our ninth planet, even as our understanding of the planet's
diminutive size became clear.
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This is about proper classification of solar system bodies, not what we are
comfortable with.
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Levy, S&T Focal Point 8/1994: ... a well-regarded textbook author has
considered changing the planet table in the back to only list eight "planets."
On what basis would he do that? Because Pluto is smaller than we thought?
Because the orbit is weird? Because it is not the Planet X that was supposed
to have affected the orbits of Neptune and Uranus? None of these is a solid
reason to launch the confusion that would result from a classification
change.
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Answering your questions in order: 1) on the basis of facts we know today,
2) Yes, 3) Yes, and 4) No. There is nothing more confusing that something
that has been misclassified. When I explain to my sixth-grade students, that
Pluto was at first misunderstood, they easily make the shift to the Eight
Planet Paradigm, no confusion, and the discussion I have with them gives them
a better, more consistent view of the solar system.
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Levy, S&T Focal Point 8/1994: Just as we see that the boundary between
a rock and a boulder is not sharp, we now are starting to see the solar
system as a continuum of objects of varying sizes.
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When one looks at the field of boulders, and picks up the largest rock from
the gravel bed, not noticing the gravel, it is natural that one might start
considering the rock a boulder. But to keep this up in light of the discovery
of the gravel bed ...
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Levy, S&T Focal Point 8/1994: ... S. Alan Stern proposed three standards
we can apply that help define Pluto as a major planet. ... As ever more
objects are found beyond Neptune we may someday have to deal with a solar
system that contains a lot more than nine planets.
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This process is backwards. Define what a major planet is, and then see what
fits. As for more objects to count as planets, we don't have to look beyond
Neptune—we already have a bunch in the Asteroid Belt. And regarding
beyond Neptune, we have 10 new planets today, eleven if you promote
Charon, by your reasoning. I now count 25 or more planets. Cool!
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Levy, S&T Focal Point 8/1994: Or, as another astronomer has suggested,
we could adopt a specific diameter, say, 1,000 km, as a dividing line. Ceres,
a minor planet, is smaller than this value, and Pluto, a major planet, is
larger.
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More than once, I have seen 1,003 km for the diameter of Ceres. Other sources
(Lowell Observatory et al) publish a value between 900 and 1,000.
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Levy, S&T Focal Point 8/1994: Historical convention is a powerful
argument for leaving well enough alone unless there is a very good
reason for change.
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There is a very good reason—we now understand the region of which
Pluto is King (so far).
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Levy, S&T Focal Point 8/1994: Changing the status of Pluto will not
alter how we study it, or planets like it, in any way at all. The frontier
of the solar system is a far more complicated place than we realized back in
1930, and in the next decade it will likely become an even more intricate
place.
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Yes, I agree, and if we do not keep pace with the change of knowledge, we will
be relegated to being the fools of the past.
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Levy, S&T Focal Point 8/1994: ... we should keep things as simple as
possible, for the sake of astronomy itself and its public perceptions.
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I agree, and it is far more complicated to delude the public just for the
sake of the image of astronomy. There is nothing simpler than understanding
that there is an ice belt on the outer fringes, and that we used to think
the first object in that belt was a planet.
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Levy, S&T Focal Point 8/1994: Let us simply enjoy and appreciate Pluto
for the fascinating body it is.
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Agreed.
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Stern, S&T Letters 11/1994: I never hear dog lovers asking whether a
poodle or a Chihuahua is a real dog ...
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That's easy - you can look at most animals and tell whether or not they are
dogs
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Stern, S&T Letters 11/1994: Simply put, Pluto was just the easiest to
find of the hundreds or thousands of small, ice-dwarf planets that
dominate the planetary population of the solar system. Who cares if
it's called a major planet or a minor miracle?
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Planetary scientists do—it is natural for a scientist to classify and
categorize (see above)
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Binzel, S&T Letters 11/1994: ... waste of your page space ...
reclassifying Pluto's planetary status takes the dog's bone ...
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I note that the entirety of your web page states, outside of name, title,
alma mater, photo, and contact info, Planetary astronomy; collisonal
evolution of asteroids; physical parameters and surface features of the
Pluto-Charon system. You have no interest at all in this matter,
do you? http://www-eaps.mit.edu/faculty/binzel.htm
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Tombaugh, S&T Letters 12/1994: From the standpoint of size, Pluto has
27 times the volume of the largest known asteroid Ceres. Mercury's volume is
only eight times greater than that of Pluto.
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Basing an argument on volume is just a variation on diameter which is no
less arbitrary. However, since you brought it up, Mars is 2.7 times the
volume of Mercury. We can live with a one-third drop in volume, but a
one-eighth drop is right out.
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Tombaugh, S&T Letters 12/1994: While we are considering reclassifying
astronomy, how about revamping the Hertzsprung-Russell diagram ... Or let's
throw out the awkward constellation system! ... Pluto started out as the
ninth planet, a supported fulfillment of Percival Lowell's prediction of
Planet X. Let's simply retain Pluto as the ninth major planet. ... Pluto was
your last chance for a major planet.
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I would imagine that the Hertzsprung-Russell diagram would be changed if
we discoverd a new spectral class of stars. I know that constellations have
come and gone, a good example being Quadrans Muralis, the only part which
survives today is the Quadrantids meteor shower. This is science, not
nostalgia. I see no significance to a numerological love of the number
nine. Eight is just as good as far as I'm concerned. You almost seemed to
suggest that there is something boring with the eight planets, and
that calling something a planet which is not a planet will somehow change
things. Nevertheless, I thank you for the hard work you put into discovering
this object in the first place.
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You're jeapardizing our space-probe to Pluto
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OK, I'll shut up now
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