Two events happened in the third week of August, 2006, that I will never forget: 1) Pluto was officially voted out of the club of major planets, and 2) my daughter was born. I remember this as I was asked to join the vote that week to determine the fate of Pluto. Instead I decided that week to concentrate on the fate of my new daughter!
As a result of that vote, Pluto is no longer a planet. Alas, we are down to 8 major planets in our solar system, or are we? It was just this year that excitement has been brewing over the possibility that there actually is a 9th planet afterall, and it is not Pluto.
This latest result is based on studying the movement of a group of minor planets called the Centaurs. The Centaurs have orbits that place them near to the orbits of the outer gas giant planets such as Jupiter, Uranus and Neptune. What is interesting is not the Centaurs themselves, but rather their orbits.
These minor planets display a curious orbital behavior such that most of them tend to have the points marking their nearest approaches to the sun in alignment. Moreover, many of them also have their orbits lined up in the same plane of the sky. This behavior would be expected if there was a major planet responsible for corralling these more minor objects into alignment over the course of a few billion years.
Based on this study, one can predict where this major planet should be in the course of its orbit about the Sun. It turns out that this new “Planet IX” should be located in a broad swath of sky roughly between Aldeberan of Taurus and the Pleiades. It will be faint, but detectable with current technology. Happy hunting!