Aug 27, 2006 12:03
Of the two recent definitions of (major) planet, I find I don't really mind either one. The first one, which would have made Pluto and Charon a double planet system, returned planet status to Ceres, and made planets of a few objects not yet formally named was reasonable. That it would make planets of a good many things bothered some, but it was a fairly simple definition.
The second definition, that required not only that an object have enough mass for gravity to make them spheroid, but also that they the space near their orbits of the majority of other bodies (or capture them as satellites or trojans) is also a sensible definition. This changes Pluto from a (major) planet to a "dwarf planet" and I'm not sure what "minor planet" means, if anything, with this definition.
While either definition is pretty reasonable, the means of the second one being adopted makes it suspect. There was a conference with well over a thousand in attendance, but the second definition was held on the last day when many had already left and only 424 voted. That bothers not only me, but others whose opinion probably actually matters in this.
It's been pointed out that Ceres was also called a (major) planet for a while, until more objects were discovered that were similar and the term asteroid invented for the group. There are objects similar to Pluto and Pluto is an oddball compared to the major planets. Its orbit is quite inclined relative to the plane of the ecliptic and its orbit is quite eccentric. While many texts will need re-writing and much fiction will seem dated, that is hardly a new circumstance. I like what someone suggested for how to consider Pluto. Rather than get too upset by Pluto losing major planet status, consider that it joins an even more exclusive group, that of the planets emeritus.
pluto,
planet,
astronomy