The solar system has 12 planets.
That is the conclusion, to be announced today, of an international panel formed to devise a scientific definition of a planet and settle an increasingly intense dispute over whether Pluto qualifies. The panel suggests retaining Pluto and immediately adding three new planets to the nine that are familiar to any schoolchild: Ceres, currently considered a large asteroid; Charon, now considered a moon of Pluto; and Xena, a recently discovered object that is larger than Pluto....
The result of this reconfiguration is a jarring new view of the Earth's neighborhood. Between Mars and Jupiter is a vast belt of asteroids, presided over by the planet Ceres, named for the Roman goddess of agriculture. At the solar system's fringes is another vast belt of icy objects, the plutons, with Xena being the largest known, slowly orbiting the sun.
There are 53 objects that meet the panel's criteria and probably many more to be discovered, according to Michael Brown, an astronomer at the California Institute of Technology who discovered Xena. (Brown dubbed the body Xena after the television series about a warrior princess, but it is officially known as "2003 UB313," and has not been given a permanent name.) The total number of planets, Brown said, could easily climb above 100....Me too. =-)
This challenging new portrait of the solar system should be seen as an opportunity, according to Michael Smith, a science textbook author and seventh-grade science teacher in Delaware. The decision helps illustrate, he said, that science is not a static set of facts, but a constant conversation. He said he was eager for school to start so that he could share the findings with his students and lead a discussion about all the different objects in the solar system, how they might be grouped, and how this might change as new information comes in.
"I am thrilled," he said.