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“This great column of solar gases which was thus separated from the sun subsequently evolved into the twelve planets of the solar system.”
~ Urantia Book, P656:3, 57:5.7, {Origin of Monmatia, the Urantia Solar System]

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Nine no longer: Panel declares 12 planets

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 new definition has been approved by the executive committee of the International Astronomical Union , and a vote of the union's general assembly is scheduled for Aug. 24 at a conference underway in Prague. If it is approved, which several astronomers said seems likely, the world's textbooks and museum displays would have to be updated -- not to mention solar system models, posters, software, and toys with only nine planets.

The change, scientists say, would be a mark of the great age of discovery that astronomy has entered over the last three decades, with the advent of space probes, powerful telescopes, and new observational techniques.

The current model of the solar system has held since 1930, when Pluto was discovered. Since then, astronomers have discovered that the solar system is a much larger, more diverse place. These discoveries, especially the findings that Pluto is markedly different from the other planets and is part of a vast cloud of frozen worlds known as the Kuiper Belt, have challenged the neat categories in the nine-planet solar system. Faced with these problems, the Astronomical Union has been struggling for years to work out its first formal definition of a planet.

Suggest mnemonic device for new solar system online at boston.com/globe

“It is wonderful when new scientific discoveries present you with new problems,” said Richard Binzel , a Massachusetts Institute of Technology professor of planetary geology who served on the panel. “This is almost the essence of being a scientist.”

The proposal defines a planet as an object that circles the sun and is massive enough that its own gravitational forces compress it into a roughly spherical shape. Depending on its composition, a planet would have to be at least roughly 250 to 500 miles in diameter to qualify. It designates a new subcategory of planet, the “pluton,” a Pluto-like planet that takes at least 200 years to circle the sun. Pluto, Charon, and Xena are all plutons, and scientists expect many more to be discovered. Under the proposal, Ceres is an ordinary planet.

Moons are excluded from planetary status, using a criterion that depends on the relative mass of two bodies that are gravitationally tied. If one body is much smaller than the other, then it is considered a moon. Pluto and Charon are closer in mass, and so they are dubbed a double planet. The Earth's moon is round and much larger than Pluto, but it is so much smaller than Earth that it is considered a moon, not a planet.