How Many Planets Are in Our Solar System?

Most of us learned in elementary school that nine planets make up our solar system. Yet those old textbooks may be in need of updating and perhaps soon. A big ball farther out than Pluto but which apparently appears to meet the standard definition of a planet challenges the conventional wisdom about the true number of planets within our solar system.

Currently assigned the inglorious name of 2003 UB313, this possible tenth planet also bears the pet name of Xena, just like the long-time syndicated show about a warrior princess. First discovered in 2003, UB313 joins at a few other possible planetary bodies now under consideration in a reevaluation of how many planets actually exist within the same solar system where Earth orbits.

Yet whether UB313 or Xena is ever reclassified as a planet, yet alone the tenth recognized one in our solar system, remains to be seen. This doubt exists for several reasons. One is the issue of these other recently discovered potential planets under review.

Another matter is the fact that a real controversy exists about whether even some of our current planets really deserve this classification. While there are planets like Earth, made of rock, there are other that are simply large, frigid, gaseous balls like Pluto. Astronomers and scientists question whether planets by the Earth definition belong in the same category as others like Pluto.

After all, we know that Earth supports life since so many of us are here. Mars, too, seems to show some early promise of having, at least at one time, offered the common elements like water that allow the formation of life.

However, the potential for life forms does not define whether a big ball becomes a planet or not. Instead, there are three classic states which each object must be deemed to meet before they can attain planetary status. These are:

1. Sufficient gravity to retain its round configuration.
2. Not so big that they could potentially become a star which can lead a quite different life from a planet.
3. Orbits a sun.