Summary: Transactions of the IAU
, Vol. XXIV B, 2001
J. Andersen, ed.
Pluto: A Planet or a Trans-Neptunian Object?
Michael F. A'Hearn
Department of Astronomy, University of Maryland, College Park MD
Abstract. The purposes of classification and taxonomy are reviewed.
Using examples from fields ranging from paleontology to planetology, I
argue that non-exclusive classifications, which allow Pluto to be consid-
ered both a planet and a TNO, provide the most desirable approach to
progress in our science.
Scientists classify things in order to find patterns that will help explain how
things are related or how they evolved. In some sciences, such as paleontology
and meteoritics, considerable effort goes into taxonomy. Much less effort goes
into taxonomy and classification in most of planetary science. Nevertheless,
discussion of the classification of Pluto in 1998-99 was surprisingly vigorous.
There are lessons to be learned from looking at other examples of classification
that are analogous to the case of Pluto. Analogies are never perfect, but they