And Then There Were Eight
Copyright © 2005 by Joel Marks Originally published with the title “Discovery of 10th planet may mean there really are only eight” in the New Haven Register on August 3, 2005 (page A6) At first I was excited to learn that a tenth planet has just been discovered in our solar system. But a moment's reflection made me realize that this probably means there are only eight planets. How could that be? The status of the ninth planet, Pluto, has been in question ever since a new category of solar system object was discovered, which are now collectively known as the Kuiper Belt. Analogous to the ring of asteroids that orbit the Sun between Mars and Jupiter, these are tens of thousands of planetoids that orbit the Sun beyond the orbit of Neptune. That is also where Pluto spends most of its time (although Pluto's eccentric orbit sometimes brings it closer to the Sun than Neptune). So there has been the surmise that Pluto may not be a planet but simply the largest member of the Kuiper Bel...