Farewell to Pluto

Even Gingerich is not satisfied with the new category of 'dwarf' planets and describes the term as clumsy and linguistically preposterous. Likewise, Alan Stern, Principal Investigator of NASA's New Horizons mission to Pluto, describes the decision as a 'terrible mess' and dislikes the unscientific idea of putting a limit on the number of planets. Although the third criterion is intended to cover objects orbiting in the Asteroid or Kuiper Belts, Stern dislikes it and claims that other planets have also failed to either absorb or knock away their orbital debris.

But coming up with a new definition was no easy matter. The committee was specifically charged with considering social and historical context when coming up with defining criteria. The choice of 'roundness' as a criterion for planetary status reflects the committee's sensitivity to the broad cultural significance and use of the term. Likewise, moons were maintained as distinct entities from planets.

Robin Catchpole of Cambridge University Institute of Astronomy believes that the new definition is the lesser of two evils. Although he would have preferred to keep Pluto on historical grounds, he had been unhappy about the original proposal to allow 12 planets. He would have preferred the term 'minor planet' to the term 'dwarf planet', but believes that the names given to objects are not really that important.

Perhaps the IAU's task was an impossible one. As far as the public was concerned, the scientists were in the familiar position of being unable to provide the certain and watertight definition required of them. Conversely, some astronomers feel they accommodated cultural context at the expense of good science.

With the IAU currently considering a dozen candidate dwarf planets, the argument about how to categorise them may have only just begun.

For more information:

Petition Protesting the IAU Planet Definition
http://www.ipetitions.com/petition/planetprotest/

Pluto Petition
http://www.plutopetition.com/