Download Sarah Hughes - Sailor Astera

The Pluto Debate
Sarah Ruth Hughes
Professor Hirshfeld
Honors Project: Part One
Astronomy 151
It has been dark for seventy-seven days. As day finally breaks, you find yourself on a barren field
of frozen nitrogen and methane. The sun appears as a bright star through the thin atmosphere; it
is so far from the planet's surface that the temperature will not reach above -333 degrees
Fahrenheit that day. On the horizon, the moon is rising. You are on the surface of Pluto, up until
now considered the ninth planet in our Solar System. But is it actually worthy of that title?
Discovered in 1930 by Clyde Tombaugh at the Lowell Observatory in Arizona, Pluto was quickly
hailed as the long sought for Planet-X. For many years, astronomers had been aware that there
was scientific evidence indicating the probability that another planet lay beyond the orbit of the
then furthest planet Neptune. Eventually, however, became clear that the ‘evidence’ for Planet X
arose from a misassumption in the mass of Neptune. In addition to that, Pluto is not large
enough to account for observed gravitational disturbances on the other outer planets. Located
about 40 times the Sun-Earth distance, Pluto has a mass that is about .2% of Earth's mass. Its
surface gravity is a mere 1/20th of Earth's. In fact, it is very similar in size and has a similar
erratic orbit to many of the new objects discovered since the 1990s in the Kuiper Belt – a
collection of icy objects that orbit the sun beyond Neptune. Gerard Peter Kuiper was the DutchAmerican astronomer that first suggested the existence of a belt of trans-Neptunian objects.
Within the last two decades, astronomers have discovered over 800 of these objects. In light of
these new discoveries, the scientific and general community has been pondering just what, in
fact, constitutes a planet.
Well, the answer is not as simple as one might think. Technically, there is no ‘official’ definition of
a planet. There had been no need to give a precise definition because, with our technology being
so limited, a planet was anything big enough to seen in orbit of the sun. The asteroid Ceres was
the first object to call attention to the lack of characterization. Giuseppe Piazzi accidentally
discovered Ceres in 1801 while searching for another night sky object. He noted the position of
the strange light; through measurements, he began to believe it to be a comet. However, it was
moving very slowly. Other professionals such as German astronomer Johann Elert Bode noted
that Ceres was in just the right location away to fill the ‘blank’ orbit between Mars and Jupiter.
Ceres was assigned a planetary symbol. However, as hundreds of such objects were discovered
in similar orbits, it became clear that this was no ordinary situation. Post-Ceres, the consensus
was that a planet must inhabit its orbit exclusively barring natural satellites. Thus over the next
200 years, our society became familiar with the Asteroid Belt: tens of thousands of relatively small
chunks of rock and ice orbiting the sun as remnants of the original matter of the solar system that,
because of Jupiter’s massive gravitational pull, never fully formed into a planet. The debate
about what was or was not a planet could then rest, for a time.
Now the debate is raging once again. In the last decade, there have been major new discoveries
of many trans-Neptunian objects (or, TNOs) including Quaoar and Sedna, both of which are only
slightly smaller than Pluto is. Most recently, in July of 2005, astronomers presented another TNO
of probably equal or greater size than Pluto. Some astronomers almost instantly hailed 2003
UB313 as the 10th planet. Presently, other astronomers consider the unnamed object to be a
minor planet – a loose term given to objects in our solar system that are larger than meteorites
but smaller than planets we are familiar with. This discovery has once again thrown the question
about the true definition of a planet into the spotlight. If this new object is larger than Pluto is,
then by some theories, it must be a planet. Other astronomer’s notions, however, would show
that this new discovery points to evidence that Pluto is just one of many Kuiper Belt objects.
Scientific professionals and the public are locked in a battle of questions as they try to come to
grasp with the new discoveries.
So what are the options for Pluto if we were to reclassify it? As mentioned, mounting evidence
does suggest that Pluto is in fact most likely on of many similar objects in the Kuiper Belt.
Perhaps astronomers falsely categorized Pluto as a planet because of the lack of understanding
of the far reaches of the solar system. The International Astronomical Union (IAU) announced in
an official press release in 1999 that there were no plans to change the status of Pluto or assign it
a minor planet number. Officially, it is a planet with an orbit around the sun, a moon and an
atmosphere. Many in both the scientific and general community argue that tradition has it that
Pluto is a planet and therefore by societal standards, it should remain so. This point of view is
reminiscent of many public reactions to new ‘truths’ as we continue to learn about the universe
we live in. It hardly seems logical to continue to follow nostalgic social norms when science, in
the pursuit of truth, finds evidence otherwise.
However, there are some problems with reclassification: a new definition for Pluto could change
how we define other objects in our solar system as well. Some astronomers believe that size
should be the determining factor in defining a planet. This creates an interesting situation for the
Solar System because the proposed cut off diameter, 700 kilometers (about 435 miles), would
add many TNOs and even some asteroids to our list of planets. Our list of planets could grow to
a dozen or more! Another common suggestion is that the shape of an orbiting body might
determine its ‘planethood.’ Under this suggestion, scientists state that a planet would be an
object that became spherical under its own gravity, thus allowing Pluto to keep the title of planet.
This presents some discrepancies because of the make up of many objects in the solar system.
Ice and rock do not compress at the same rate, thus some larger objects made of rock might not
form as spheres when smaller icy objects would. There is also the matter of defining just how
spherical an object would have to be to gain the title of planet.
Perhaps it is time to develop a new classification for the objects that orbit our sun. I am reminded
fondly of nights spent with my father enjoying Gene Roddenberry’s “Star Trek” series in which the
fictional inter-stellar human space explorers discussed the habitable Class M terrestrial planets
and Class C geologically inactive planets that rested desolate in the cold outer regions of a star
system. With the discovery of more complex space objects, it might become necessary to not
only more frequently redefine our ideas about our universe, but also to create names and
definitions to suit these objects we find. These classifications could take into account so many
specifics that they could foster clearer definitions of celestial objects more scientifically than
culturally. Eventually, these scientific definitions would become commonplace in society as well.
Thus, science would reclassify Pluto, but it would not be any less important than other created
classifications of objects in orbit around our star. History would preserve Pluto as the object
formerly known as the ninth planet.
Just as the idea of a spherical Earth was unacceptable and hard to comprehend for many of the
people in the time of Pythagoras and Aristotle, the notion of changing our views on Pluto seem to
threaten to the status quo. However, in the face of new discovery let us not forget that throughout
human evolution new information has provoked new knowledge and greater understanding. With
this new understanding, our society must come to terms with the idea that our universe will
constantly surprise us as we probe greater depths. It is up to the scientific community to pursue
scientific truth to present the clearest possible image of the space in which we exist, even if at
present it contradicts the popular notion. After all, what is popular is not always true.