There’s a fascinating article, Is Pluto a planet after all?, by Stephen Battersby in the July 27, 2009 New Scientist about the continuing controversy over whether Pluto is a planet. It shows how scientific discourse reflects multiple cultural and political forces, why defining any word is hard, and how our continuing transactions with nature lead us to think again.
How many planets are in the solar system? The official answer is eight – unless you happen to live in Illinois. Earlier this year, defiant Illinois state governors declared that Pluto had been unfairly demoted by the International Astronomical Union, the authority that sets the rules on all matters planetary.
Click on the image to see the New Scientist diagram, which explains part of the debate.
Of course, Pluto is still a planet. It is disingenuous to say the “official” planet count in our solar system is eight, as that decision was made by only four percent of the IAU, most of whom are not planetary scientists. It was immediately opposed by hundreds of professional astronomers in a formal petition led by Dr. Alan Stern, New Horizons Principal Investigator.
The IAU definition makes no sense in stating that dwarf planets are not planets at all, a departure from the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto’s orbit, according to this definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another location is essentially useless.
The IAU should take responsibility for the highly flawed definition adopted by only four percent of its members, most of whom are not planetary scientists, in 2006. However, the IAU should not be viewed as the sole authority on the definition of planet. Many planetary scientists do not belong to the IAU. Should they not have a say in this matter? Something does not become fact simply because a tiny group that calls itself an authority says so. It is significant that hundreds of planetary scientists led by New Horizons Principal Investgator Alan Stern immediately signed a formal petition opposing the IAU definition.
There are other venues through which a planet definition can be determined, such as last year’s Great Planet Debate at the Johns Hopkins University Applied Physics Lab. Audio and video proceedings from this far more balanced conference, which I was fortunate to attend, can be found at http://gpd.jhuapl.edu/ . You can also read more about this issue on my blog at http://laurele.livejournal.com .