Words are frequently at the root of controversy. On August 24, 2006 the controversy came to light over the word “planet”. Do you remember the news stories and glib comments spoken by media figures? How about, “Honey, I shrunk the Solar System.” Or “Pluto has been demoted.”
The current controversy of Pluto being reclassified as a dwarf planet began to heat up in 1992. Astronomers discovered another major object beyond the orbit of Neptune. Soon they found thousands of similar orbiting objects. The area of the outer Solar System is now known as the Kuiper Belt.
Suddenly the International Astronomical Union (IAU) was faced with a dilemma. If an object is a planet, the naming of it is the responsibility of the IAU group for planetary-system nomenclature. The default group is the “Minor Planet Center”. Uncertainty over which committee names the objects led to the Pluto designation crisis.
Discussions and debates ensued about definitions of planets, moons and other objects in the Solar System. The IAU realized that a major public relations problem was probable when the release of the new definitions were made public. The largest organization of planetary scientists agreed with the IAU. However, the American Astronomical Society disagreed.
The Americans insisted the public statement must acknowledge that dynamical evolution about our knowledge of the Solar System be included. The result of that proposed wording was the statement that a planet is “the dominant object in its local population zone”. However, that ambiguous wording wasn’t satisfactory to the committee. An even more fuzzy statement replaced it. A planet “cleared the neighborhood around its orbit.”
Finally, in Prague, on August 24, 2006 the IAU adopted their official Definition of a “Planet” in the Solar System. Here is the main portion of the resolution:
“The IAU therefore resolves that “planets” and other bodies in our solar system be defined into three distinct categories in the following way:
1. A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit. 2. A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
3. All other objects except satellites orbiting the Sun shall be referred to collectively as “small solar-system bodies.”
It appears that the controversy is not over. Astronomers have been circulating a petition to overturn the IAU decision. Astronomer emeritus at Harvard University, Owen Gingerich, says the definition is “confusing and unfortunate”. Furthermore he said he was “not at all pleased”.
Meantime, the head of the team who discovered Pluto, Mike Brown of Caltech, was philosophical. He said, “As of today, I have no longer discovered a planet. The public is not going to be excited by the fact that Pluto has been kicked out. But it’s the right thing to do.”
The Blue Jay of Happiness thinks the controversy is a good opportunity for us to learn about the workings of science.