This epitomizes what true science is about: refining our knowledge to better understand nature. At first, only Pluto’s motion across the sky was known. Then the size and distance were estimated. Then its moon was resolved and later the moon was shown to be a co-planet. Finally the sizes, masses, and location of Pluto and it co-planet were shown to be just two of many bodies in a belt of rocks at that orbit within the solar system. When science had established a new definition of planet, it was only logical to reclassify Pluto.
Pluto is easily observable with modest telescopes. When it was discovered, Pluto moved across the [apparently] static background of distant astronomical objects, just like the other planets in their orbits. The time scale of Pluto’s orbit proved it must be within the solar system. Later, other minor planets’ were discovered in the Kuiper belt within the solar system, one of them larger than Pluto!
Rather than rule the new minor planet our tenth planet while more and more minor planets were discovered, the International Astronomical Union redefined planet. A planet had to orbit the sun (Pluto barely meets this criterion since the center of its orbit lies between it and its largest moon/co-planet Charon). A planet must be able to gravitationally pull it into a spherical shape. A planet must have cleared the neighborhood of its orbit. Pluto absolutely fails the last criterion because its mass is only 7 percent of the mass in its own orbit. Earth’s mass is 1.7 million times the mass in its own orbit!
Compared to historical shifts in the understanding of the nature of the universe, Pluto’s reclassification is insignificant. Much more controversial and perspective-shattering revelations included the realization that Earth is not in the center of the solar system, that there is no center to the universe, that not all of the visible astronomical objects are contained within our own galaxy, and that the galaxies are accelerating away from one another.
It seems to me that it is only tradition and sentimentality keeping everyone from letting Pluto go. There is no legal or scientific basis to maintain the old solar system model. Scientific models are meant to be continuously refined and updated as better knowledge comes along, just as computer chips get smaller and faster as we learn better ways of manufacturing them and designing them. It’s progress.
