It might not be classified as a "planet" anymore, but that doesn't mean it is isn't still interesting. Go here to read how recent observations of the original "plutoid" suggest some bizarre behavior of its atmosphere.
Tuesday, May 11, 2010
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Pluto IS still a planet. 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.
As a dynamic world with geology and weather, Pluto shows it has more in common with the other, bigger planets than it does with most Kuiper Belt Objects except the few large ones, which should be considered planets too. Most KBOs in Pluto’s orbital path are tiny and do not have these features. These images show that before making definitive classifications, we should first get the data and analyze it; otherwise, we are defining objects without knowing significant factors about them.
Okay:
(1) Just because a decision wasn't made by the entire IAU doesn't make it invalid. The IAU has rules, I believe they were followed.
(2) Dr. Stern's definition is a perfectly valid one, and he is definitely an experiment on this subject, but his definition of a "planet" is not the commonly accepted one. One problem I personally have with it is that it doesn't take into account any information on the formation of the object. The formation of KBOs and asteroids is inherently different from that of what is now considered planets - asteroids did not clear out their orbit, and KBOs didn't form in the thin region of the proto-planetary disk that existed around the Sun as it formed. Maybe the definition of a planet shouldn't incorporate this information, but maybe it should.
(3) Most importantly - why does it matter? Pluto is Pluto regardless of what we humans call it. Planet is a human-defined term whose definition has changed considerably over time as our understanding grew, and should continue to do so.
1. The IAU violated its own bylaws in adopting the 2006 resolution. Those bylaws state that a resolution must first be approved by the appropriate IAU committee before being sent to the floor of the General Assembly for a vote. This was not done. Instead, the IAU rejected the resolution recommended by its own committee, which would have included Pluto, Ceres, and Eris as planets. Many members left the two-week conference assuming that resolution, which had been worked on for months, would be the one on the floor. A small group rushed through a different resolution, the one that ended up passing, on the last day of the conference, not just in violation of IAU bylaws, but also an act that equaled a deception of those members who had left expecting the other resolution to be up for a vote. Many said had they known a different resolution would be put to the floor, they would have stayed to oppose it.
2. There is no "commonly accepted definition" of planet as of now. There are two competing viewpoints, the dynamical perspective, which is the IAU view, and the geophysical perspective, many planetary scientists in addition to Stern uphold. That definition is based on what an object is rather than where it is and defines a planet as any non-self-luminous spheroidal body orbiting a star.
Pluto and Ceres did not form the way asteroids did either. Their being large enough to be rounded by their own gravity is an important factor that distinguishes them from asteroids. They simply are smaller planets.
We have now discovered exoplanets, giant planets, in wildly eccentric orbits around their stars, systems with giant planets in 3:2 resonances like Neptune and Pluto, a planet that orbits its star backwards, and a planet that formed directly from a molecular cloud, the way stars form. Clearly, a broader definition of planet is needed to encompass this diversity. We can use subcategories to distinguish types based on various factors including how they formed.
3. What we call objects matter because that is how we make meaning out of the world around us. How many people were taught about Ceres in school? When it was downgraded (wrongfully, as it is in hydrostatic equilibrium), it stopped being taught in schools, and knowledge of it faded into oblivion.
Referring to dwarf planets as not planets is inconsistent with the use of the term dwarf in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Furthermore, it blurs the distinction between planets and asteroids by not acknowledging a difference between those objects large enough to be shaped by their own gravity and those that are simply shapeless rocks.
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