I decided to write about why Pluto was declassified as a planet. As you'll see, it really isn't a planet. It's more of a "dirty snowball," a comet that wasn't given proper fuel. I won't spoil the ending. Instead, I'll allow the research to speak for itself.
Deep-Sixing Pluto—How the Little Guy Lost His Planetary Status
In 2006
The International Astronomical Union made a decision that has
impacted both astronomy, and our view of the universe. They gave
Pluto the sailor's elbow, and declassified our former ninth planet to
mere “Dwarf Planet” status. This was a controversial decision,
one that has lead many to say, “How dare they?” But it has also
lead astronomers to ask the question, “What constitutes a planet?”
Originally, the word planet was simply the Greek word for “wanderer.”
But now, a new debate has been created as to the exact definition of
planethood. How this is defined will shape our view of the universe.
Tombaugh in 1930. Among his accomplishments Tombaugh was awarded the Rittenhouse medal in 1990.
Pluto
was discovered by astronomer Clyde Tombaugh in 1930. Initially,
Tombaugh was on the hunt for a presumed gas giant, that was believed
to affect Neptune's orbit. Since then Astronomers have learned that
such a spare gas giant does not exist. However, Tombaugh did find
something else in the process. He found a spec that was moving
across the sky at night. It tread step by step, while the stars
appeared static. Tombaugh recognized it as another one of these
classically-named “wanderers” in the night sky. The result was
that soon a new planet was added to our solar system; the first to be
discovered by an American. It was dubbed “Pluto,” after the Greek
lord of the Underworld. And its distance from Sol, our sun, was such
that it was thought to be an icy and barren world.
As it
turns out Pluto is indeed icy and barren. Its surface contains frozen
methane (natural gas), nitrogen, and even carbon monoxide. Its
average temperature is 25K (Kelvin, the coldest temperature scale on
record). It also has polar ice caps, much like our own Earth, and our
closest neighbor, Mars. However, The temperatures on Pluto fluctuate
greatly, yet they are still incredibly frigid. It has often been
depicted as a tiny blue dot, with the distant rays of the Sun barely
reaching it. It is a lone wanderer, an orphan in a sky full of
giants.
When I
was a child, I was taught that our solar system had nine planets. But
as time went on astronomers began to doubt this. Pluto sits in a
region of space known as The Kuiper Belt—a dense band of asteroids
and similar objects. It extends from outside of Neptune's orbit at 30
AU (Astronomical units. Codified by the distance from The Sun to
planets) to about 1000 AU. The Kuiper Belt functions as both an
umbilical, and a nursery. It the birthplace of comets, but also the
afterbirth of the Solar System. It is where the ice, dust, and rock
that made planets such as our own can be found. It is the leftover
material of worlds set adrift. It is a reminder of our past, long
before Earth had finished accretion. As early as 1992 objects far
larger than Pluto were sighted in this region. Yet, they were also
not classified as planets. Why is this so? As it turns out, when it
comes to planets, size does matter.
Pluto
was originally thought to be nearly the size of Earth. It was also
believe to be the possible cause of a perceived eccentricity in
Uranus' orbit. But with further observation it was discovered to only
be 2300 kilometers in diameter. It could easily fit inside Earth
several times over. It would boggled the mind to think how many times
it could fit inside of a gas giant such as Jupiter. Further more, its
mass far lower than Earth's own moon. It also turned out that the
so-called anomalies in Uranus solar orbit were just computational
errors. Indeed, size does matter when it comes to planets. To put it
bluntly, Pluto just doesn't measure up. It's not tall enough to ride
the planetary roller coaster.
Another
reason for the mislabeling of Pluto as a planet was lack of
knowledge. Little was known about the Kuiper Belt in 1930. Even less
was known about the objects beyond Neptune. These so-called
trans-Neptunian objects, such as Eris and Makemake are better
understood now. But in Tombaugh's time telescopes just weren't
sensitive enough to find them. This was an era before anyone had
literally set foot in space—let alone sent a space-based telescope
such as Hubble. The tools available to Tombaugh at the time were not
too dissimilar from those used by Galileo and Sir Edmund Halley.
Telescopes, a keen eye, mathematical equations, and a lot of patience
were the astronomer's equipment until the space age.
Image from NASA's Hubble Space Telescope in 2012. Pluto and its moons.
Planetary
politics also plays a role in why some astronomers won't let Pluto
stay in the underworld. NASA has undertaken some very necessary, and
expensive, missions in recent years. They range anywhere from Mars
colonization projects, to the exploration of Europa (one of Saturn's
moons). Most recently NASA sent Rosetta, a robotic hitchhiker that
thumbed a ride on a comet, the first mission of its kind. Despite
being a success with that mission, and others, NASA has to continue
to justify its funding. Congressional purse-strings for a mission
like New Horizons (the probe that will observe Pluto) would be firmly
drawn shut if Pluto were just a mere hunk of ice. The mission will
cost NASA $700 million, and take over a decade. With a bill like that
it's no wonder that self-interest will play a factor in future fiscal
decisions. The sad truth of scientific funding, and the perpetual
lack there-of, comes to the fore. It's not only a matter of prestige
for NASA. It is also a matter of job security for a multitude of
engineers, physicists, and launch crews.
The
final nail in Pluto's coffin (yes, pun intended, as Pluto was lord of
the underworld) was its own orbit. The International Astronomical
Union used this as their criteria to define a planet. It wasn't
Pluto's distance from our Sun, as such. It was more a case of Pluto
chugging along with little fuel in its engine. As codified by the IAU
a planet must “Clear its orbital neighborhood.” To explain
further I must first give the IAU's full definition of a planet.
Three criteria were chosen for this now technical definition. Ancient
Greek philosophers like Aristotle would have loved to argue this
definition, just as astronomers and the public do today.
First, a
planet must orbit a star (not another planet). This is why large
moons like Titan and Europa are not considered planets. They orbit
Saturn, not the sun.
Second,
it must attain hydrostatic equilibrium. This means that it has a mass
large enough to sustain gravity, and accreted into a spherical shape
(planets just aren't square or rectangular).
Third,
and this is the key point, it must be “gravitationally dominant.”
In doing so it must clear it's own neighborhood. That means that
there are no objects larger than itself nearby. There are several
trans-Neptunian objects that dwarf Pluto several times over. Also
Pluto takes a ridiculously long time to orbit Sol (our local star,
the Sun). It takes 248.6 Terran years for Pluto to orbit the sun.
This means that it wasn't even one Earth year old when it was
declassified as a planet. In cosmic terms it was barely out of its
adolescence. Though Pluto does have natural satellites (Charon, Nix,
Hydra, P4, and P5) the mere presence of them is not enough to elevate
Pluto to planetary status. The presence of these natural satellites
doesn't count for much. Mercury and Venus have no satellites, and yet
they are full-fledged planets. What Pluto does qualify as is a “dwarf
planet.”
The IAU
defines a dwarf planet in similar, but slightly altered terms.
First,
it must orbit a star. Okay, that's pretty straightforward there.
Second,
it must have a spherical shape due to hydrostatic equilibrium. Pluto
is good on that criterion as well.
Third,
it must clear it's orbit.
Fourth,
it must not be a satellite.
In other
words; Pluto is defined as dwarf planet by what it is not, not what
it is. The main differences between the two classes of planets are
not necessarily size-based (per the IAU's definition) rather it is
based on orbital path. The size issue is more one that astronomers
use are part of their anti-Pluto arguments. One that does make sense,
as Pluto is basically a small comet without a tail. If it were
ignited, it would have been Comet Pluto, and been a more rare visitor
than Hally's eponymous comet. It may be a dwarf planet to some, but
to call it that would be refer to it as a planet at all.
In
conclusion I agree that Pluto is not a planet, or even a dwarf
planet. It should properly be referred to as a trans-Neptunian
object. That tells us immediately what it is, and what it is not. It
is an object that is beyond the orbit of Neptune. It does not clear
it's own orbit. And it is part of the Kuiper Belt. It's greater claim
to fame should not be that it was once thought of as a planet, but
that it is residue from the creation of the solar system. Pluto is a
bit of left-over building material that was not used to make a rocky,
Earth-like planet, or serve as the core of a Jovian gas giant.
Instead, it is there as a reminder of what could have been...and what
once was. In that instance further study of this trans-Neptunian
object is required. By understanding Pluto we will understand the
nature of the our solar system. We will have a sort of baby picture
of where we came from...and a preview of where we might be going.
Works Cited
Comins,
Neil F. Discovering The Essential Universe (Second edition).
pp. 138-140. New York.
W.H.
Freeman and Company. 2004. Print.
“IAU
2006 General Assembly.” International Astronomical Union
Website. IAU. N.D. Web.
“Pluto,
Perception & Planetary Politics.” Jewitt, David and Luu,
Jane X.
Daedalus,
Vol. 136, No. 1, On Nonviolence & Violence (Winter, 2007),
pp. 132-136. MIT Press American Academy of Arts & Sciences. http://www.jstor.org/stable/20028095
“The
Problem with Pluto: Conflicting Cosmologies and the Classification of
Planets.” Messeri, Lisa R. Social Studies of
Science, Vol. 40, No. 2 (April 2010), pp. 187-214. Sage
Publications, Ltd. Stable http://www.jstor.org/stable/25677402
Piantadosi,
Claude A. Mankind Beyond Earth: The History,
Science, and Future of Human Space Exploration. Columbia
University Press, January 2013. Digital.
http://www.jstor.org/stable/10.7312/pian16242
Yeomans,
Donald K. Near-Earth Objects: Finding Them Before They Find Us.
New Jersey. Princeton
University Press, November 2012. Digital.
http://www.jstor.org/stable/j.ctt1r2fck
.
Blogger's Note: The images in this post did not accompany my original paper. They were added by me for some extra flair. My final grade: 10 out of 10!
Text Copyright R.J.X. Joyce 2015
All images are taken from NASA.
All images are taken from NASA.
No comments:
Post a Comment