My son S is trying to resolve the planet-no planet issue over Pluto. He’s a big fan of the planets and doesn’t want to hear about this kind of subtraction. On the one hand, I think it’s good scientific practice to put definitions through the consistency test. On the other, the answers seem to lead to more questions. The basic phenomenon of a solar system appears simple on the system: first there’s a sun with different types of objects acting “systematically” in its vicinity according to certain relational reactions. Orbits can be tracked, classes of objects chalked up, forces measured and observed.

But it seems to me that Pluto remains a mystery. Despite the power of probes, Hubble, and other telescopes, nearly everything scientists know about Pluto comes from a distance and from pretty good inference. I’d suggest stipulation as the approach for this kind of decision. Why not? I myself don’t like Pluto as a planet. I’ve never really understood the decisions made about Pluto in the excitement over the need for a ninth back at the Lowell Observatory. Pluto might have resolved Neptune’s mistaken perturbation, but this would not come to pass. Little could have been understood after Pluto had been observed–size, mass et cetera.

But, there you have it.