The Emporia Gazette

Ad Astra

Planet Pluto is NOT history. Please do not blindly accept the controversial demotion of Pluto, which was done by only four percent of the International Astronomical Union, most of whom are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. Stern and like-minded scientists favor a broader planet definition that includes any non-self-luminous spheroidal body in orbit around a star. The spherical part is important because objects become spherical when they attain a state known as hydrostatic equilibrium, meaning they are large enough for their own gravity to pull them into a round shape. This is a characteristic of planets and not of shapeless asteroids and Kuiper Belt Objects. Pluto meets this criterion and is therefore a planet. Using this broader definition gives our solar system 13 planets and counting: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris. At the very least, you should note that there is an ongoing debate rather than portraying one side as fact when it is only one interpretation of fact.

January 26, 2011 at 12:38 p.m. ( permalink | suggest removal )

Last Leg of the Journey

Pluto IS a planet because unlike most objects in the Kuiper Belt, it has attained hydrostatic equilibrium, meaning it has enough self-gravity to have pulled itself into a round shape. When an object is large enough for this to happen, it becomes differentiated with core, mantle, and crust, just like Earth and the larger planets, and develops the same geological processes as the larger planets, processes that inert asteroids and most KBOs do not have.

Not distinguishing between shapeless asteroids and objects whose composition clearly makes them planets is a disservice and is sloppy science.

As of now, there are three other KBOs that meet this criterion and therefore should be classified as planets—Haumea, Makemake, and Eris. Only one KBO has been found to be larger than Pluto, and that is Eris.

The IAU definition makes no linguistic sense, as it states that dwarf planets are not planets at all. That’s like saying a grizzly bear is not a bear. Second, it defines objects solely by where they are while ignoring what they are. If Earth were placed in Pluto’s orbit, by the IAU definition, it would not be a planet. That is because the further away an object is from its parent star, the more difficulty it will have in clearing its orbit.

Significantly, this definition was adopted by only four percent of the IAU, most of whom are not planetary scientists. No absentee voting was allowed. It was done so in a highly controversial process that violated the IAU’s own bylaws, and it was immediately opposed by a petition of 300 professional astronomers saying they will not use the new definition, which they described accurately as “sloppy.” Also significant is the fact that many planetary scientists are not IAU members and therefore had no say in this matter at all.

Many believe we should keep the term planet broad to encompass any non-self-luminous spheroidal object orbiting a star.
We can distinguish different types of planets with subcategories such as terrestrial planets, gas giants, ice giants, dwarf planets, super Earths, hot Jupiters, etc.

We should be broadening, not narrowing our concept of planet as more objects are being discovered in this and other solar systems.
In a 2000 paper, Dr. Alan Stern and Dr. Hal Levison distinguish two types of planets—the gravitationally dominant ones and the smaller ones that are not gravitationally dominant. However, they never say that objects in the latter category are not planets.

I attended the Great Planet Debate, which actually took place in August 2008, and there was a strong consensus there that a broader, more encompassing planet definition is needed. I encourage anyone interested to listen to and view the conference proceedings at http://gpd.jhuapl.edu/ You can also read more about this issue on my blog at http://laurele.livejournal.com

You can find the petition of astronomers who rejected the demotion of Pluto at: http://www.ipetitions.com/petition/pl...

December 30, 2008 at 5:39 p.m. ( permalink | suggest removal )