In preparation for tomorrow’s meeting of Dark Skies, Bright Kids, we decided to test our comet making skills before we unleashed 17 elementary school kids upon our activity. We’re making a physical analog of a comet, with dirt, water, sand, syrup (for the organic molecules), and a little bit of ammonia (a spritz of glass cleaner), all frozen over with dry ice. All we had today was a little bit of dirt I dug up outside the astronomy department (shhh, don’t tell the groundskeepers), some water, and the dry ice, but we had to get an idea of how much material we would need tomorrow for each kid to have a comet, and how best to pack these things together. Educators, always practice your demos! For your own sanity.
The best way to get things good and cold is to use really fine dry ice. So we gave Paul a hammer and set him on his way to go all 2001 on it.
I’m going to smash it, WITH A HAMMER!
Make some mud, mix in some ice, pack together… voila! Your very own outgassing comet!
Gail gives her outgassing comet a little help
They are dark, just like real comets. Although we think of them as bright, icy objects, their albedos are actually quite low. (Albedo is a measure of how reflective an object is, where 0 is completely black and 1 is perfectly reflective.) Astronomers use infrared and optical telescopes to measure the size, brightness, and albedo of comets and find them to be as dark as asphalt! So our frozen mudballs were pretty close. Also, as it warms, you can see the carbon dioxide gas come off, and if you are really good, blow it out into a tail.
Do NOT handle dry ice with your bare hands. I’m not very bright.
I hope to soon get pictures of the kids making comets as well! But of course, we don’t have image release forms from all their caregivers just yet, so enjoy the big kids playing with dirt for now.
And as the C’ville resident comet person (tho yeah, I’m not affiliated with you guys), I’ll point out that the geometric albedo of comets is between 0.04 and 0.06 meaning that comets only reflect about 4 to 6 percent of the light they receive from the sun. The average for the other flying rocks (ie asteroids) is about 15% and that’s skewed high thanks to silicate compositions, ie things like Vesta.
Hey Erin!! If you like working with kids, you should join our band of merry outreach makers 🙂
It still boggles my mind that something that we characterize as being icy is so much darker than something we characterize as being a rock. 4 or 5% is like a road surface…. or what “Mount Chipotle” looks like now over at Barracks…
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