In 2006 the (now) dwarf planet Pluto lost its status as a planet because it did not meet the three criteria of the International Astronomical Union (IAU). Any planet that does not meet these criteria is now classified as dwarf planets. Poor Pluto.
These three criteria are as follows:
1. It has to be in orbit around the Sun.
2. It has sufficient mass to assume a hydrostatic equilibrium. (def: a state of balance by which the internal pressure of a gaseous body, such as a star, exactly balances its gravitational pressure.)
3. It has cleared the neighbourhood around its orbit.
Pluto has the first two of these criteria but loses out on the last one. By clearing the neighbourhood, the IAU means that the planet needs to be gravitational dominant and that there are no other bodies of comparable size, other than its own satellites in its vicinity of space. Planets cannot have any hangers-on other than their moons.
For a little background, we will discuss a bit about this little brother of the Solar System. (Just as a side note: why is it that our Sun and Solar System are referred to as such even though there is millions of each in the universe? I would think that if we ever did run into off-worlders it would be quite confusing. I hereby declare the Sun as Stan and the Solar System as Spinny-Whirlygig.) Pluto was discovered at the Lowell Observatory in 1930 by American astronomer, Clyde Tombaugh with assistance from William H. Pickering at a period of time of intense planet hunting. Everybody wanted to find the next planet. It resides in the Kuiper belt, a circumstellar disc in the outer Solar System of small bodies or remnants from the time it was formed. It is similar to an asteroid belt but much, much larger. Some of the Solar Systems moons, such as Saturn’s Phoebe and Neptune’s Triton, actually came from the Kuiper belt.
The discovery of this ‘planet’ was news around the world. The naming of it was the right of the discovering observatory and many different names were recommended and tossed about but the name Pluto, the god of the underworld, was settled upon. Rumour has it that a famous cartoon mouse’s dog was named after it although the animator never confirmed this.
Pluto has five know moons: Charon, Styx, Nix, Kerberos, and Hydra; all names having connection to the underworld just like their anchor. Charon is the largest with its diameter being just over half of Pluto itself. They are sometimes referred to as a binary system because the centre of their masses does not fall within either body but somewhere between the two and they follow an orbit around it. (This can happen when two celestial bodies are close in mass.)
Pluto’s orbit is what can be described as chaotic. Unlike other planets in the Solar System that follow a flat reference plane in a nearly circular orbit, Pluto is moderately inclined in comparison in a more elliptical shape and then you throw in that weird dance between it and Charon and you have quite to eccentric orbit. Its orbital period is 248 years, meaning that has not even finished one orbit since its discovery. The truly interesting thing about its orbit is that scientists cannot predict its future orbit because it is so sensitive to outside influences.
New research at the University of Central Florida in Orlando concludes that Pluto’s demotion to planetoid/dwarf planet is based on flawed reasoning. You can read the reason here but basically it states that the definition is one of semantics and based on a concept which nobody uses in their research anymore. The moons Triton and Europa have often been described as planets throughout history since Galileo as well as many, many others celestial being referred to as planets which violate the IAU definition. “It’s a sloppy definition,” Philip Metzger, UCF planetary scientist said of the IAU’s definition. “They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.”
Metzger went on to say that Pluto is much more interesting than many of the other planets. It has an underground ocean, a multilayered atmosphere, organic compounds and evidence of ancient oceans and lakes. It is much more dynamic than Mars; in fact, the only other planet in the Solar System that is more complex is Earth. So, take out your placards and fight for the reinstatement of Pluto as a planet! It deserves to up there with the big boys.
*As a final note, I would like to say that I find it funny that the university that is championing this is centered near the magical land where a certain cartoon dog may be finding the demotion of Pluto especially demeaning but maybe that is just me.
–Janice Willson
Here is a very cool ‘fly-by’ done by NASA using more than 100 images stitched together. Take a look:
https://commons.wikimedia.org/wiki/File:PIA11709_-_A_Colorful_%27Landing%27_on_Pluto_(Animation).ogv
