Picture Credit: International Astronomical Union
Would you believe that until now, no one has really defined what a planet is? As our knowledge of the solar system has expanded, the question of "planet status" has been a tough nut to crack. We have moons around Jupiter and Saturn that are bigger than Pluto and asteroids that are round and in their own private orbits. Beyond Pluto we keep discovering big round objects that match the classical interpretation of a planet, except they are in highly elongated orbits and take over 200 years to go around our sun.
The International Astronomical Union has been charged with the job of deciding just what is a planet and what isn't. Within the next week, the IAU membership will vote on a draft resolution to redefine the accepted view of our solar system and text books will never be the same again. The discovery of big round planet-like objects beyond Pluto forced the issue.
If accepted by the IAU membership, the new interpretation will promote the asteroid Ceres to planet status. Pluto's former moon Charon will be a planet and we have at least one other -a new planet which hasn't yet been formally named (The popular title is Xena but it's not official. Scientists refer to it as 2003 UB313 while they figure out a permanent name)
Under the new system it's a planet if it's big enough to be round (or nearly so), if it orbits around a star, as well as not being a star itself. Earth's moon doesn't qualify because it orbits around the Earth. Pluto's fomer moon Charon is now a planet because both Pluto and Charon orbit around their common center of gravity which exists somewhere between them in space.
With this new interpretation, there will be many more additions to the solar system's tally of planets. There are a number of candidates already lined up for consideration and I'm sure there will be more with time.
Comments