If Pluto could speak, it would say, 'Define
planet'
By Allan R. Andrews
American Reporter Correspondent
This commentary was posted originally in
April, 1998, in
the online daily newspaper, The American Reporter.
WASHINGTON -- Here's an ongoing story that, quite literally, is
way out.
Is the celestial body known as Pluto a planet or is it not?
Many Americans, as did Chris Trejbal, a writer for the Daily Minnesotan
at the University of Minnesota, memorized the order of the planets in our
solar system with a pneumonic sentence such as, "My Very Energetic Mother
Just Served Us Nine Pies."
The planets hide in the initial letters of the nine words of the sentence
(not in the nine pies): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,
Neptune and Pluto.
Of course, between 1979 and 1999, the last two words have to be reversed
because Pluto's weird orbit places it inside the orbit of Neptune through
that period. That's just one of the ways, as Trejbal notes, that Pluto misbehaves.
Astronomers have known for a long time that Pluto differs from the other
eight planets in several ways; its size; its icy material; its rotation;
its path around the sun; its relationship to its moon, Charon, which is bigger
than most moons in relation to the planets they orbit. Each of these has raised
questions about Pluto's status beyond the stratus.
Now, however, several astronomers are arguing that Pluto should be demoted
from the world of planethood.
Let me back up.
Pluto was discovered in February of 1930 by an amateur astronomer, Clyde
W. Tombaugh, and at the suggestion of an 11-year-old girl from Oxford, England,
the new discovery was called Pluto.
Tombaugh is the only American to discover a planet, which immediately puts
a socio-political twist on the current debate over Pluto's status.
Tombaugh lived to a grand age of 90, and died in 1997 just a month short
of the 73rd anniversary of his discovery. As long as he was alive, the astronomy
community seemed content to suppress the debate over Pluto out of respect
to his inspiration.
Information gathered by the Hubble Space Telescope in 1996 fed the debate
over Pluto and convinced scientists like Brian Marsden, who wears the elaborate
mantle of Director of the Central Bureau for Astronomical Telegrams of the
International Astronomical Union, that the planet status of Pluto is a "long-standing
myth."
Astronomers have known at least since 1978, when the planet's moon, Charon,
was discovered, that Pluto's size had been overestimated. Writing in the
Atlantic Monthly in February, science writer David H. Freedman pointed out
that "Seven moons in the solar system are bigger than Pluto."
The killer discovery, though, came in the 1990s when the so-called Kuiper
Belt was found to be made up of 60 or more Pluto-like objects hurtling through
the solar system. Freedman writes that for many astronomers, Pluto appeared
to be just a slightly larger version of one of the Kuiper Belt objects.
Freedman points out that textbook writers are beginning to question Pluto's
planethood and that one of the most widely used new texts refers to Pluto
as an "interplanetary body."
The real problem with Pluto, however, as almost every writer and thinker
on the subject admits, has little to do with Pluto's substance and a lot
to do with astronomy's definition of a planet.
As Freedman writes: "It would help if 'planet' had a formal definition
against which Pluto could be measured, but none exists."
Trejbal is more frank: "The problem, the deep dark secret that astronomers
don't want you to know, is that they have no idea what a planet is. . .
. What neither [students] nor the astronomers can tell you are the precise
conditions that qualify one object as a planet and another as not."
At a fascinating Web site he maintains, Lowell observatory astronomer Marc
W. Buie offers a standard working definition for a planet:
http://www.lowell.edu/users/buie/pluto/pluto.html
"A planet is a special term applied to the larger members of our solar
system. Rule #1, a planet must orbit the Sun. Rule #2, it must be large
enough that its own gravity is strong enough to maintain a spherical shape."
Buie reasons, "Trying to stuff Pluto into the Comet bin would clearly be
wrong. Pluto is far too big to behave anything like the tiny chunks of ice
we call comets. Could Pluto be considered an asteroid? Well, you might be
tempted because Pluto is so small.But consider the fact that Pluto has enough
gravity to be spherical and retain a significant atmosphere. It also probably
has an active surface and very pronounced seasons. These characteristics
sure do make it sound more like the other planets than the asteroids."
Trejbal believes the International Astronomical Union (IAU), which will
make the determination on Pluto's taxonomy in the next few years, is going
to eliminate Pluto from the ranks of the planets, though he offers several
romantic and popular reasons for not doing so.
"As Americans," he writes, "we hate to see it lost as it is the only planet
discovered by one of our countrymen, and our inherent love of the underdog
gives Pluto a special place in many of our hearts."
Buie suggests a third category of planet be added to the existing two (rocky
and gaseous), which would allow Pluto to remain a planet.
This debate seems to boil down, as do so many, to where one's heart rests
rather than where one's head travels.
I asked my sixth-grader if Pluto is a planet. "Yes, it is," he responded
without hesitation.
"How do you know?" I inquired.
"We learned it in third grade," he said, and moved on.
With a little stretching, his answer fits my concept of an operational
definition, one of the linchpins of modern science.
I'm for Pluto as the ninth planet.
Allan R. Andrews is a former news editor for The Stars & Stripes in Washington,
D.C. He can be contacted at andrews852@verizon.net