Nov

21

All Solar Systems Go.

Posted by Christopher Waldrop

November 21, 2008 |

pluto1.jpgSky & Telescope, in its December issue, reports on the ongoing debate about the status of Pluto. Yes, there’s still debate. The International Astronomical Union may have demoted Pluto to a vague non-planet status in 2006, but that hasn’t settled anything, even in the minds of scientists. At least part of the problem seems to be linguistic rather than scientific—which is probably where most of the trouble is. Language doesn’t always make sense, and, by its nature, resists the kind of rigidity that scientists would like. Pluto has been classified as a “dwarf planet”, but does that make it a non-planet? Scientist David Morrison says, “It’s grammatically and logically weird to have ever passed a rule saying that a dwarf planet is not a planet…given that astronomers recognize dwarf stars as a type of star and dwarf galaxies as galaxies.”

The article notes that most critics are really fine with Pluto being called a “dwarf planet”, but the problem is where to draw the dividing line. The asteroid Ceres is only about 950 kilometers in diameter—less than a third of Pluto’s size—but it still fits two of the IAU’s criteria for “planet” status. It orbits the Sun and has enough gravity to be round. Does that mean it’s a “dwarf planet” or do we keep calling it an “asteroid”? Neil deGrasse Tyson may have put it best when he said, “The word planet has lost all scientific value.” Possibly it’s even lost all value to us non-scientists as well, although the word “planet”, derived from the Greek for “wanderer”, has already had a history of flexibility. Four planets—Jupiter, Saturn, Uranus, and Neptune—are basically giant balls of gas. Some of us think of a “planet” as an object we can stand on, but the gas giants don’t have a surface we’d recognize or a place to put our feet. The same issue of Sky & Telescope has another article called “Titan: Earth In Deep Freeze”, pointing out the similarities between Earth and Titan, but Titan’s a moon. And yet it’s also bigger than the planet Mercury.

Obviously the debate will go on. In a toy catalog I got in the mail last week there was a model solar system that was described as having eight planets, while this do-it-yourself Solar System kit at Enchanted Learning includes Pluto but calls it a dwarf planet. The Great Explorations 3-D Solar System Kit (where were these when I was a kid?) says, “Hang all 9 Planets From Your Ceiling”. Do we take the word of toymakers or scientists? Maybe neither. Personally I’m sticking with my own definition. Pluto is a planet, and I think the definition of “planet” should be allowed to wander.

pluto.jpg


Comments

3 Comments so far

  1. Andrea on November 21, 2008 9:17 am

    I never understood that Pluto controversy either, but I did get that solar system set for my kid last Christmas! It’s pretty cute.

  2. Baino on November 21, 2008 3:26 pm

    Pluto is definitely a planet! Silly scientists! Adam used to have a glow in the dark solar system suspended from the ceiling until the dinosaurs came along . . then Darth Vader . . the the lego technics - now it’s posters of motorbikes!

  3. Christopher Waldrop on November 21, 2008 4:35 pm

    The whole controversy seems to be about distinctions. What’s a moon? What’s a planet? What’s an asteroid? The distinctions are a lot fuzzier than scientists would like. I think they should just come up with their own terms and let the rest of us call Pluto a planet.

Name (required)

Email (required)

Website

Speak your mind

<< Post Navigation >>

« « Just The Fax. | Word Of The Week: November 22nd, 2008 » »