17 August 2006

Quiz: How Many Planets in the Solar System?

If you said 9, you’re not correct… not anymore:

(hat tip, Wes)


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.

But the group's proposal also makes clear that many more objects in the solar system -- perhaps dozens of them -- could qualify as planets after further study.

There are 53 objects that meet the panel's criteria and probably many more to be discovered… The total number of planets, Brown said, could easily climb above 100.



The key issue is how a planet is defined. One way to define it is anything big enough to have a spherical shape* that orbits the sun. But it’s also reasonable to define “planet” to refer only to the largest satellites in the solar system, i.e. those that coalesced in to large masses as the solar system was forming (the "evolutionary" view). Looking at it this way would basically give you only 8 planets (excepting Pluto).


*Physics Factoid: There is a limit to how big or long an object can be and still retain its shape. Once an object gets big enough, its own gravity forces it into a spherical shape. It’s impossible to build a bridge to the moon, for example, because nothing can be that long and stay linear. After it gets to a certain length it will compress itself and never get longer. And if you keep adding mass it will turn into a sphere eventually.

5 comments:

Michelle Fry said...

I heard this story on NPR this morning and I'm thinking the whole thing isn't going to take but what do I know? I think it's odd that Jupiter and it's moon will both be considered planets but the moon won't. Why mess with a good thing?

KatieG said...

hmmm, i'll leave outer space to the scientists....

did you go see Roddick this weekend?

WestEnder said...

I did not see Roddick, but I'm glad he's pulling it together this summer. He was a finalist at Indianapolis (where he won the doubles) and now he's won Cincinnati. Good to see that.

He said he has "as good a chance as anyone not named 'Roger'" to win the Open.

Blake is still my dark horse. Of all the people who could beat Federer, I think he is the only one I'd be happy for.

But let's face it: this U.S. Open will only have one story, and that's Agassi.

KatieG said...

that's funny...I'm a Roger fan, but would love to see Blake have a good showing. Yeah, Agassi's face is all over the subway stops and billboards out this way.

I'm going tuesday with a day-pass to the grounds, and thursday night i'm going to sit in Arthur Ashe for the evening match.

howard said...

Is it Xena? I thought it was Sedna. Anyway, to the Oort cloud there is a long way to go.