Posted by DrJeff on July 10th, 2009
Copyright 2009 | About this blog
This post is a Dr. Jeff’s Jeffism.
Last week on BotU, I used boat-loads of wrapping paper to gift wrap the Moon. I can’t believe that I actually bought TOO MUCH of the stuff! What to do with the leftovers, what to do. Hey, I know! I’ll wrap the largest asteroid Ceres! (Oops … can I say that? Are the IAU police listening?)
What? You don’t know what I’m talking about? Don’t you remember the whole ‘Is Pluto a Planet’ thing in 2006? Well it spilled over to poor old Ceres. In its infinite wisdom, the International Astronomical Union—the IAU—renamed Ceres a “Dwarf Planet” ’cause what they did to Pluto had a ripple effect across the Solar System. BUT they forgot to let the rest of us know if we should still call Ceres an asteroid. Or maybe they just don’t write very well (see below.)
So you know what? I’m going to call it a dwarf planet AND the largest asteroid. “Now, now kids, don’t fight …Shimmer … it’s a floor wax AND a dessert topping (SNL.)”
Now for the cool part—
If I gift wrapped Ceres the largest asteroid, I’d need a piece of wrapping
paper 4 TIMES THE AREA OF TEXAS!
Certainly Texans can appreciate that. Another way to say it (and here’s the Jeffism)—
If I wanted to explore the entire surface of the largest asteroid Ceres,
it would be like exploring an area 4 times the size of Texas.
That’s a BIG rock.
1. Have your class check my calculation. See if the surface area of Ceres is approximately 4 times the size of Texas.
Hint: the surface area of a sphere = 4 x pi x r2 where r is the radius of the sphere
2. Discuss with the class why precise definitions in science (or any subject) are important. You can use my “Frustrations with the IAU” section below to explore the specific problem with the definition for Ceres.
Dr. Jeff’s frustration with the IAU:
Here it is, the ‘official’ FAQ taken directly from the International Astronomical Union web site. As you all know, FAQ stands for FREQUENTLY asked question. So the IAU felt it very important to clarify their position on the FREQUENTLY asked question “What is Ceres?” And now, the IAU rersponse—
Q: What is Ceres?
A: Ceres is (or now we can say it was) the largest asteroid, about 1000 km across, orbiting in the asteroid belt between Mars and Jupiter. Ceres now qualifies as a dwarf planet because it is now known to be large enough (massive enough) to have self-gravity pulling itself into a nearly round shape. [Published reference for shape of Ceres: P. Thomas et al. (2005), Nature 437, 224-227. Dr. Peter Thomas is at Cornell University.] Ceres orbits within the asteroid belt and is an example of a case of an object that does not orbit in a clear path. There are many other asteroids that can cross the orbital path of Ceres.
Dr. Jeff pondering: Hmmm, now that’s what I call a really crisp answer. I’m no longer puzzled. “Ceres is (or now we can say it was) the largest asteroid …” certainly seems very consistent with “There are many OTHER asteroids …” Hey IAU, do you guys really read what you write? Here, I’ll help you with a rewrite, and just say you’re going with Answer 1 or Answer 2, so we can all know how to have a conversation about Ceres:
Q: What is Ceres?
Answer 1: Ceres has been reclassified as a dwarf planet because … [fill in dwarf planet definition here.] Note it is no longer considered an asteroid.
Answer 2: Ceres has been reclassified as a dwarf planet because … [fill in dwarf planet definition here.] It is, however, still considered an asteroid. Other objects in the Solar System have dual, even triple status (because we the IAU say so). Pluto is now a dwarf planet AND a Trans-Neptunian Object AND a Plutoid.
(Would you put trust in definitions concerning your Solar System from an organization that cannot write simple FAQs? I don’t.)
IAU—Intentionally Against Understanding.
Photo credit: NASA, ESA, and J. Parker (Southwest Research Institute)
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