Please tell your children to stay in school.
8
Pluto in the Elementary School Classroom
A PERSONAL RECOMMENDATION FOR EDUCATORS
YES, IT REALLY IS OFFICIAL. PLUTO IS NOT a red-blooded planet, as voted in August 2006 by the general assembly of the International Astronomical Union. Pluto is now a “dwarf” planet.
How rude.
The vote overturned the Planet Definition Resolution proposed by the Planet Definition Committee, which had stated simply that round objects in orbit around the Sun are planets. Pluto is a round object. Therefore, Pluto is a planet. This first attempt to define “planet” would have given everyone the right to utter Pluto and Jupiter in the same breath even though Jupiter is 260,000 times larger than Pluto. Plutophiles had about a week to rejoice before learning the sad news that Pluto fails a new criterion—that a legitimate planet must also dominate the mass of its orbital zone. Poor Pluto is crowded by thousands of other icy bodies in the outer solar system.
Embarrassing as it was to us all, the term planet had not been formally defined since the time of ancient Greece.
In 1543, Nicolaus Copernicus published his thesis—his newfangled, Sun-centered (heliocentric) universe, which confounded the wanderer classification scheme. Instead of being stationary and in the middle of things, Earth moved around the Sun just like everybody else. From that moment on, the term planet had no official meaning at all. Astronomers just silently agreed that whatever orbits the Sun is a planet. And whatever orbits a planet is a moon.
Not a problem if cosmic discovery freezes in time. But shortly thereafter, we learned that comets orbit the Sun too, and are not, as long believed, local atmospheric phenomena. Are they planets too? No, we already had a name for them: comets. They’re the icy objects on elongated orbits that throw a long tail of evaporated gases as they near the Sun.
How about the craggy chunks of rock and metal that orbit the Sun in a region between Mars and Jupiter? Hundreds of thousands roam there. Are they each a planet too? While first called planets—beginning in 1801 with the discovery of Ceres—it became rapidly clear as dozens more were discovered that this new community of objects deserved its own classification. They came to be called asteroids.
Meanwhile, Mercury Venus, Earth, and Mars form a family of their own, being relatively small and rocky, while Jupiter, Saturn, Uranus, and Neptune are large and gaseous, have many moons, and bear rings.
And what’s going on beyond Neptune? Beginning in 1992, icy bodies were discovered that look and behave a lot like Pluto. Yet another swath of populated real estate was discovered, akin to the discovery of the asteroid belt two centuries before. Known as the Kuiper belt, in honor of the Dutch-born American astronomer Gerard Kuiper, who championed its existence, this region of the solar system contains Pluto, one of its largest members. But Pluto had been called a planet since its discovery in 1930. Should all Kuiper belt objects be called planets?
Without a formal definition for the word planet, these questions created years of debate among people for whom counting planets matters.
If my overstuffed in-box is any indication, planetary enumeration remains a major pastime of the elementary schools and a deep concern of the print and broadcast media. Counting planets is what allows you to invent clever mnemonics to remember them in sequence from the Sun, such as “My Very Educated Mother Just Served Us Nine Pizzas.” Or its possible successor: “My Very Educated Mother Just Served Us Nachos.” Here’s one that may grow on us all: “My Very Educated Mother Just Said Uh-oh No Pluto.”
Where do you go from there? Because of exercises such as this, elementary school curricula have unwittingly stunted an entire generation of children by teaching them that a memorized sequence of planet names is the path to understand the solar system. The word planet itself continues to garner profound significance in our hearts and minds. This was surely justifiable before telescopes let us observe planet atmospheres; before space probes landed on planet surfaces; before we learned that icy moons make fertile targets for astrobiologists; before we understood the history of asteroid and comet collisions. But today, the rote exercise of planet counting rings hollow and impedes the inquiry of a vastly richer landscape of science drawn from all that populates our cosmic environment.
Suppose other properties matter to you instead. Suppose you care about ring systems, or size, or mass, or composition, or weather, or state of matter, or proximity to the Sun, or formation history, or whether the cosmic object can sustain liquid water or liquid anything. These criteria represent demographic slices that reveal much more about an object’s identity than whether or not its self-gravity made it round or whether or not it’s the only one of its kind in the neighborhood.
Why not think of the solar system as families of objects with like properties, and the cut through these properties is yours to take. Interested in cyclones? You get to talk about the thick atmospheres of Earth and Jupiter together. How about auroras? That conversation would include Earth, Jupiter, and Saturn, since all three have magnetic fields that guide charged solar particles to their poles, rendering their atmospheres aglow. How about volcanoes? That would include Earth, Mars, Jupiter’s moon Io, and Saturn’s moon Titan, whose eruptions are likely driven by ice and not by lava. How about wayward orbits? That would have to include comets and near-Earth asteroids, themselves putting life on Earth at risk. The list of ways to envision and organize the solar system is long and likely endless.
Imagine a solar system curriculum that begins with the concept of density. A big idea for third graders, but not beyond their grasp. Rocks and metals have high density. Balloons and beach balls have low density. Divide the inner and outer planets in this way, as cosmic examples of high and low density. Have fun with Saturn, whose density, like that of a cork, is less than that of water; unlike any other object in the solar system, Saturn’s material would float in a bathtub.
At no time are you counting things. At no time are you worried about the definition of a taxonomic category. At no time are you left in search of a mnemonic on the premise that to understand the solar system you must memorize the proper names for things.
Eventually, you might be curious about the joint criteria of roundness and isolation. It’s undiscriminating enough to combine into the same category tiny, rocky, iron-rich Mercury and large, massive, gaseous Jupiter—at which point you remember that way back in August of the year 2006, the International Astronomical Union created a name for that class of object. You search the organization’s archives, find the word planet, and then quickly move on to the rest of what piques your interest in the solar system.
9
Plutologue
AT A JULY 2008 MEETING IN OSLO, NORWAY, THE EXECUTIVE Committee of the IAU approved a proposal49 from the IAU Committee on Small Body Nomenclature for the name plutoid to classify all dwarf planets that one might find orbiting beyond Neptune. As of this printing, two dwarf planets orbit there—Pluto and Eris—with many more surely to come. This obviously makes Pluto a plutoid. By IAU rules, Ceres, another dwarf planet in the solar system, does not receive this honor because it orbits between Mars and Jupiter in the asteroid belt. Odd that Pluto’s moon Charon is excluded, as are any yet-to-be-discovered round moons of dwarf planets beyond Neptune. An arbitrary, but enforceable, rule.
Alan Stern, now of the University Space Research Association, does not like the plutoid class for many reasons astrophysical, but when interviewed, he typically leads with “It sounds like ‘hemorrhoid.’”
He and I finally agree on something.
By August 2008, Pluto’s pitbull, Mark Sykes, was at it again. He and others organized a conference for planetary experts to discuss what to do about classification schemes for the solar system, with little to no regard for IAU proclamations. Held at the Applied Physics Laboratory of Johns Hopkins University in Maryland, the conference included a heavily touted public forum titled “The Great Planet Debate.”50 Given my history with the subject, I fe
lt somewhat accountable for things, so I agreed to debate Sykes himself, in a reprise of our impromptu conversation in my office six years earlier. But this time we had a moderator—NPR’s Science Friday host, Ira Flatow. On entering the auditorium, Mark and I were showered with “Let’s Get Ready To Rumble” entry music, commonly played as professional wrestlers enter the ring.
I am pleased to report that Mark was much more polite and cordial than I had ever remembered him to be. And at times, I was the one who was manic. But in the end, we did not converge on the definition of a planet. We both agreed, however, that the IAU had body-slammed Pluto on this one. And that a more enlightened solution to the problem awaited us all.
In an attempt to achieve closure, I took a pilgrimage to Orlando’s Disney World. I felt duty-bound to alert Pluto (the dog) of my role in his demotion. After initial dismay, or at least what looked like dismay in a creature that cannot frown, Pluto and I became fast pals, and he has accepted his uncertain fate with grace and dignity.
Meanwhile, nobody is quite sure how Pluto (the ex-planet) feels about all this except, perhaps, cartoonists. Nearly 4 billion miles away, Pluto, a cosmic object by any name, offers the last word:
Letter from Siddiq Canty, Mrs. Koch’s second-grade class, Roland Lewis Elementary School, Tampa, Florida (spring 2008).
Appendix A
Pluto Data (2008)51
Discoverer
Clyde W. Tombaugh
Date of discovery
February 18, 1930
Mass (kg)
1.27 × 1022
Mass (Earth = 1)
2.125 × 103
Equatorial radius (km)
1,137
Equatorial radius (Earth = 1)
0.1783
Average density (g/cm3)
2.05
Average distance from the Sun (km)
5,913,520,000
Average distance from the Sun (Earth = 1)
39.5294
Rotational period (days)
-6.3872 [rotates backwards]
Orbital period (years)
248.54
Average orbital velocity (km/s)
4.74
Orbital eccentricity
0.2482
Tilt of axis (degrees)
122.52
Orbital inclination (degrees)
17.148
Equatorial surface gravity (m/s2)
0.4
Equatorial escape velocity (km/s)
1.22
Visual geometric albedo
0.3
Visual magnitude (Vô)
15.12
Atmospheric composition
Methane, nitrogen
Appendix B
“Planet X”
Complete lyrics © 1997, 2006 by Christine Lavin Music (ASCAP)
Administered by Bug Music http://www.christinelavin.com
Reprinted with permission
In Arizona at the turn of the century,
astromathematician Percival Lowell
was searching for what he called “Planet X”
’cause he knew deep down in his soul
that an unseen gravitational presence
meant a new planet spinning in the air
joining the other eight already known
circling our sun up there.
But Percival Lowell died in 1916
his theory still only a theory
’til 1930, when Clyde Tombaugh
in a scientific query
discovered “Planet X”
3.7 billion miles from our sun
a smallish ball of frozen rock,
methane and nitrogen.
It joined Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus, and Neptune
our solar system’s newest neighbor
two-thirds the size of our moon
a tiny, barely visible speck
Cold! Minus 440 below.
Not exactly Paradise,
they named the planet Pluto.
That same year, 1930, Walt Disney
debuted his own Pluto as well
but a cartoon dog with the very same name as the CEO of Hell
was not your normal Disney style
most figured he was riding the coattails
of Pluto-mania sweeping the land
(not unlike our modern love for dolphins and whales).
For the next five decades mysterious Pluto
captivated our minds
as late as 1978 its own moon Charon
was seen for the very first time
but now telescopes and satellites
and computer calculations
say that Pluto may not be a planet at all,
creating great consternation.
(Some scientists say)
That Pluto is a “trans-Neptunian interloper”
swept away by an unknown force
or a remnant of a wayward comet
somehow sucked off course
others say that Pluto is an asteroid
in the sun’s gravitational pull
but if you ask Clyde Tombaugh
he’ll tell you “That’s all ‘bull’.”
“I get hundreds of letters from kids every year,” he says,
“It’s Pluto the planet they love.
It’s not Pluto the comet,
It’s not Pluto the asteroid
they wonder about above.”
And at the International Astronomical Union Working Group
For Planetary System Nomenclature
They too say that Pluto is a planet
reinforcing Clyde Tombaugh’s view of nature.
Norwegian Kaare Aksnes,
professor at the Theoretical Astrophysics Institute
He too says that Pluto is a planet
and a significant one, to boot
but at the University of Colorado
astronomer Larry Esposito
says “If Pluto were discovered today,
it would not be a planet. End of discussion. Finito.”
He says that it was not spun off from solar matter
like the other eight planets we know.
By every scientific measurement we have
is Pluto a planet? No!
and now 20 astronomy textbooks
refer to Pluto as less than a planet
I guess if Pluto showed up at a planet convention
the bouncer at the door might have to ban it.
St. Christopher is looking down on all this
and he says, “Pluto, I can relate.
When I was demoted from sainthood
I gotta tell you little buddy,
it didn’t feel real great”
and Scorpios look up in dismay
because Pluto rules their sign.
Is now reading their daily Horoscope
just a futile waste of time?
It takes 247 earth years
for Pluto to circle our sun.
It’s tiny and it’s cold
but of all heavenly bodies
it’s Clyde Tombaugh’s favorite one.
He’s 90 now and works every day
in Las Cruces, New Mexico
determined to maintain the planetary status
of his beloved Pluto.
But how are we going to deal with it
if science comes up with the proof
that Pluto was never a planet.
How do we handle this truth?
As the Ph.D’s all disagree
we don’t know yet who’s wrong or who’s right
but wherever you are, whatever you are,
Pluto, we know you’re out there tonight.
And in the year 2003
you’re going to see
the NASA Pluto Express
fly by and take pictures
of your way cool surface
to send to this web page address:
h t t p colon slash slash d o s x x dot colorado dot edu slash
<
br /> plutohome dot h t m l
You’ve got your own web page!
For a little guy,
you’ve made quite a splash!
Yes, at the turn of the 20th century
astromathematician Percival Lowell
in his quest for “Planet X”
started this ball to roll,
but at the end of the 20th Century
we think he may have been a little off base
so we look at the sky
and wonder what new surprises
await us in outer space.
Appendix C
“I’m Your Moon”
Complete lyrics © 2006 by Jonathan Coulton
http://www.jonathancoulton.com
Reprinted with permission
They invented a reason.
That’s why it stings.
They don’t think you matter
Because you don’t have pretty rings.
I keep telling you I don’t care
I keep saying there’s one thing they can’t change
I’m your moon.
You’re my moon.
We go round and round.
From out here,
It’s the rest of the world
That looks so small
Promise me you will always remember
Who you are.
Let them shuffle the numbers.
Watch them come and go.
We’re the ones who are out here,
Out past the edge of what they know.
We can only be who we are
Doesn’t matter if they don’t understand
I’m your moon.
You’re my moon.
We go round and round.
From out here,
It’s the rest of the world
That looks so small.
Promise me you will always remember
Who you are.
The Pluto Files: The Rise and Fall of America's Favorite Planet Page 12