Monday, August 14, 2006

Pluto be or not Pluto be? That is the question!

In a few days the International Astronomical Union (the international community of scientists who decide on all things cosmic) will meet to decide whether or not Pluto will continue to be classified as a planet. Before we all raise our torches and pitchforks and storm the meeting taking place in Prague, let’s consider the possibilities.

The discovery of 2003 UB313, or Xena as it is known by its discoverer, Michael Brown of the California Institute of technology, calls into question a simple phrase know to school children everywhere. It goes like this: My Very Excited Mother Just Served Us Nine Pizzas. The first letter of ever word in the sentence equates to a planet in our solar system and its order relative to the distance from the sun. Mercury. Venus. Earth. Mars. Jupiter. Saturn. Uranus. Neptune. Pluto.

Traditionally we have been taught that our Solar System encompasses nine planets. There’s also a lot of other stuff out there floating within and beyond our nine planets. Between Mars and Jupiter, for example, is a belt of debris called the Asteroid Belt. Could this belt be a failed rocky planet? Who knows? All I know is that whenever a giant asteroid threatens to destroy all life on Earth, it usually hails from this convention of rocky material.

Beyond the Asteroid Belt are four large gaseous planets. They must be having fun out there because they are fat, happy and having ball. (Pun intended, thank you.) Go past the gigantic party animals and you find a belt of small icy stuff called the Kuiper Belt.

The Kuiper Belt consists of billions of floating pieces of prehistoric ice and rock. When I say prehistoric, I don’t mean like during the rein of the dinosaurs, I mean pristine examples of objects that exist in a form almost unchanged since the formation of the Solar System. The Kuiper Belt is said to be responsible for most short period comets, as well. One of those objects is Pluto. In fact, if Pluto were to drift close to the sun it would eject a tail just like a comet and currently solar wind is blowing off a small amount of matter from Pluto every day.

The Kuiper Belt officially extends from past Neptune to 50 AU (Astronomical Units or the distance from the Earth to the Sun.) That’s far and it’s a lot of stuff. When Astronomer Clyde Tombaugh discovered Pluto in 1930 it was a happy accident. While looking for erroneous perturbations in the orbit of Neptune, astronomers searched for a planet that might be “tugging” gravitationally on Neptune. Tombaugh happened to find Pluto but it was later shown that the calculation of Neptune’s mass was in error and there was no such influence.

Side Note: This is the same way Neptune was theorized to exist. The tugging of its gravity on Uranus caused observational discrepancies with the proposed motion. This computation was correct and thus Neptune was found in 1846. Interestingly, Galileo’s drawings of his observations of Jupiter show that he first observed Neptune in the early 1600s, but because the planet was in retrograde (when the Earth overtakes another planet’s orbit as observed from Earth that planet seems to reverse its orbit) he did not notice its motion. Thus he was first to see Neptune but because he did not know he was looking at a planet (he thought it was a star) he was not credited as the first to discover it. This says much for Galileo’s observing and calculating skills. How many of us can go out with a very crude telescope and start observing Jupiter, its moons, and accidentally discover a planet, although light pollution was not a factor back then and he didn’t have The Sopranos to watch on Sunday nights.

It was a coincidence that Pluto just happened to be where Tombaugh thought he should look. After a long process figuring out what to call the new planet, Pluto was finally named for the mythological guardian of Hades. The astronomers thought that Pluto’s minor controversy was over with but the debate on Pluto would show up again seventy-five years later when Brown discovered 2003 UB313 or Xena.

Another Side Note: Which came first, Mickey Mouse’s dog or the ninth planet? In 1930 the planet Pluto was discovered and named and in the same year Disney introduced a new character. The cartoon pet of various characters who eventually became exclusively Mikey Mouses pal was named for the newly discovered planet and, in a roundabout way, for the Roman god of the underworld.

The problem is that Xena is a little larger than Pluto. So what is an astronomer or textbook writer to do? Is Xena the tenth planet? Even though it sounds like an easy question, it is not. Xena was not the first Kuiper Belt Object discovered. Hundreds have been spotted that seem to resemble planets, like Pluto.

The debate goes like this: Is Pluto a planet or just a Kuiper Belt Object we discovered early in the twentieth century before we really knew there was a Kuiper Belt? And what is the official definition of a planet anyway?

Well, that is what this conference is supposed to resolve. Certain characteristics have been bandied about for years such as: A planet must be a certain size (bigger than Pluto) or shape (round). But with those criteria, more objects discovered in recent years can be considered planets too. We run the risk of being overwhelmed with planets or having Pluto face the knife.

In my opinion (not that anyone at the International Astronomical Union will ask) is that, no matter what we decide going forward when we define what is or is not a planet, Pluto should be “grandfathered” into the clause. For one thing, thousands of school children have learned that Pluto is a planet and that our Solar System has nine of them. There is no harm in continuing that into the future.

Pluto was discovered during a golden age of astronomy when we were pushing the limits of what was defined as the universe at large. Einstein reformulated the physical world and Hubble was observing that what you saw out there was not as it seemed, but expanding at an astounding rate. Since 1930 we have discovered many other objects in the sky but none have (until Xena) threatened to unbalance the model of the solar system we all know and love. In fact, everything else has added to the wonder that is our little neighborhood within the Milky Way.

No matter what the outcome, Pluto needs to be preserved. Many of us grew up to become well-adjusted citizens without once worrying whether there are eight, nine or ten planets or if Pluto is officially a planet or a Kuiper Belt Object. It doesn’t make sense to proliferate the planetary model with hundreds of minor planetoids just to keep the logic of Pluto-as-planet in tact. For posterity’s sake, we should just say that Pluto is a planet in the traditional sense; one of nine objects that circle the sun. The nuances can be sorted out in advanced Astronomy classes in college with people who really care, or therapy if it comes to that.

Besides that, if we get rid of the planet Pluto, is Mickey Mouse’s dog the next to go?

2 comments:

The Phoenix said...

This is an interesting little debate, that's for sure. I posted about the discovery of Xena a year ago. It might've been my second post ever, actually.

ObilonKenobi said...

I think I remember reading that post.