THE SOUTHWORTH PLANETARIUM
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43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded
January 1970
2021-2022: XXXV
"I could be bounded in a nutshell and count myself a king of infinite
space, were it not that I have bad dreams."
-Shakespeare


THE DAILY ASTRONOMER
Monday, October 25, 2021
Poor Pluto

____________________________
As a few people have brought this issue to my attention within the last
week, I thought it best to address it in the DA today.
_____________________________

[image: d4xkbh7-e9334dff-9a9b-4525-9e96-05afbad6f2c4.jpg]

Astronomers are proud of their ability to predict future events with an
astonishingly high degree of certainty, provided, of course, that any given
event isn't exceedingly far in the future.   All the same, leading members
of the International Astronomical Union, the global body capable of
exerting demi-divine dominion over all celestial matters,  are perplexed
and more than a little annoyed that the Pluto issue persists despite the
lapse of fifteen Earth years.  To this day,  even quaint little planetarium
directors like myself who will often be seen reclining comfortably within
tree hollows while drawing on a fragrant pipe, are often made to answer the
question,  "Why isn't Pluto a planet, anymore?"   Some who ask that
question are mildly curious, others a bit distraught.    Whenever presented
with that query, I hasten to assure the interlocutor that, not being part
of the IAU,  I had no hand in the decision.  Moreover, I  say, had I been
given the opportunity to participate in the deliberations, I would have
been a steadfast proponent of Pluto's continued planetary status.   I then
explain the history.

*August, 2006*
A exquisitely beautiful summer month marred by the type of heart-wrenching
grief that could wither even the heartiest souls.   In August, 2006, the
International Astronomical Union convened its 26th General Assembly in
Prague.   Ordinarily,  IAU gatherings prove to be about as Earth-shattering
as rose petals wafting down a canyon.  That year, however, was different,
because toward the conference's conclusion, they deliberated about Pluto's
fate.  Or, more correctly, they voted on resolution 5A,  "Definition of a
planet." As one can well imagine, this issue sucked so much oxygen out of
the room that the other resolutions, such as # 3:  "Re-definition of
Barycentric Dynamical Time," or # 1 "Precession Theory and Definition of
the Ecliptic," caused nary a quiver among the general populace.

The planet definition issue had remained unresolved for quite some time.
In fact, defining a planet had become problematic ever since American
astronomer Clyde Tombaugh (1906-1997) discovered Pluto in 1930.
 Although it was initially believed to have been responsible for the
inexplicable perturbations in Neptune that prompted an all-out search for a
planet beyond its orbit, Pluto was soon discovered to be far less massive
than first calculated:   too small to cause the "tugs."      Also
troublesome was  its high inclination angle of 17 degrees. The other
planets are aligned more or less around Earth's orbit, or ecliptic.  With
the exception of Mercury (inclination = 7 degrees), all the other planets
have inclination angles less than 2.5 degrees.    Pluto seemed to be quite
an outlier.

Was Pluto really a planet, some wondered, or was it merely a glorified rock
tumbling around the outer solar system?  The controversy had precipitated
so many pointless wars and shattered so many otherwise blissful marriages
that the IAU felt compelled to adjudicate the matter.    In August 2006,
they settled the issue..or, at least, thought they did.

They re-defined "planet" and, in so doing, deprived Pluto of its coveted
planet status.  According to the new IAU guidelines, in order to be
classified as a planet, a celestial body must meet three criteria:

First, that body must be moving along a Sun-centered (heliocentric) orbit.
 Millions of bodies, including asteroids and comets, meet this criterion.
In fact, only moons of other worlds do not.    The moon, for instance,
cannot be considered a planet because its parent body is a planet.

Secondly, the body must be somewhat spherical. If a body is sufficiently
massive, its own gravity will overwhelm its rigid structure and mold it
into a spherical shape.     The four largest asteroids appear somewhat
spherical:

[image: 1200px-The_Four_Largest_Asteroids.jpg]

While most asteroids are irregularly shaped, such as those featured below:

[image: OSC_Astro_13_01_Gaspra.jpg]

The third criterion, however, is the tricky one.    In order for a
Sun-orbiting, spherical body to be considered a planet, it has to have been
sufficiently massive to have drawn all nearby objects into itself.    Pluto
fails on this count owing to its proximity to the Kuiper Belt, a disc of
cometary nuclei from which all short period comets, those with orbital
periods equal to or less than 125 years, originate.     Had Pluto been
heftier, it would have incorporated many proximate objects into itself and
cleared its debris field.     It isn't heftier and it orbits around many
small bodies within the Kuiper Belt, hence its demotion.

Or, at least, that was the conclusion of many IAU members who voted on the
resolution.  That vote, itself, turns out to be part of the story because
only 450 astronomers, equivalent to 3.8 Happy Hours,  were present for the
vote:  a minute fraction of the nearly 10,000 IAU members.  While a
statistician would insist that this group constituted a representative
sample of the whole population, those of a more democratic bent  might
argue that Pluto's fate was decided by only a handful of astronomers.  They
say that it should have been voted on by all the members of the IAU -as
well as planetarium directors.     The other issue that rankled many
pertained to nationalism.    You see, Pluto was the only planet in our
solar system discovered by an *American!*
                                          [image: Unclesamwantyou.jpg]

And it was demoted by a deliberative body consisting largely of *Europeans!*

                                        [image:
Gérard_-_Louis_XVIII_of_France_in_Coronation_Robes.jpg]

Hence, perhaps, the protracted continuation of a controversy that the IAU
tried to settle more than a Jovian year ago.       Although Pluto still
bears the ignominy of its scarcely deserved demotion, its advocates aren't
surrendering...at least not yet.



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