How Many Planets Are Really in Our Solar System?
This weekend astronomers suggested that 2003UB313—a large, round, trans-Neptunian object (TNO) in the Kuiper belt—is our solar system's tenth planet.
2003UB313 is larger than Pluto, which argues for it gaining planet status. Personally, however, I'm not sure that Pluto should count as a true planet, but as a minor planet—one of many minor planets in the Kuiper belt. Its orbit is unlike that of any of the eight undisputed planets, and it is smaller than the earth's moon (as is 2003UB313). The only planet nearly as small as Pluto is Mercury, which is located close to the sun, where one expects to find smaller, rocky planets. (One other possibility is that Pluto and its moon, Charon, form a double planet.)
If we do consider Pluto a planet, then 2003UB313 must also be certified as a planet and given a name that is easier to remember. My fear is that astronomers will continue to find large objects in the Kuiper belt that argue for planet status. Before long, we will have dozens of planets in the solar system, and third grade science will suddenly become much more difficult.
posted by Tinley | 8:18 AM
1 Comments:
I come down on the other side. But it's important to begin with the point which Dr. Michael Brown, the new object's discoverer, made only today: there is, in fact, absolutely no scientific definition of the word "planet" to begin with.
Never was. It's purely a cultural term, not a scientific one.
Is size the issue? Several moons in our solar system, including our own, would then qualify as planets.
Certainly the gas giants- Jupiter, Saturn, Uranus and Neptune- are as different from the rocky, terrestrial planets in the inner solar system as either are from Pluto or the new object- which, in view of its affinity with Pluto and its eccentricity, I propose be named "Goofy."
Goofy and Pluto both have moons. Know anything that has moons other than planets? Granted, Goofy, Pluto, Sedna, Quaoar, and undoubtedly other, future candidates for planethood are far outside the plane of the solar system. But Venus orbits the sun in the wrong direction. What eccentricities are so fundamental to the concept as to be disqualifying, and which aren't? Why?
My own hunch is that the IAU will shortly come up with the first scientific definition of the term "planet" in history. I think it will be something like this: An object sizeable enough to be formed roughly into a sphere by its own gravity, orbiting no primary but the Sun. Pluto, Goofy, Senda, Quaoar, and Ceres will all become planets. But for the first time, the concept will have an actual definition, and we won't be left arguing about something which, at the moment, is merely a matter of personal taste.
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