If your students know anything about the moon, they are probably familiar with its crater-pocked surface. They might not know that Mercury has plentiful craters of its own, and if they don’t know that, they certainly don’t know why the two celestial bodies’ craters are so different from each other. Well, guess what, chief? Today’s the day you teach ‘em all about that schwa, thanks to this handy dandy Demo Science science demo.
Drip Drip Splat Splat Whoa Oh Oh
For this one, you’ll need a big bowl—doesn’t need to be very deep, but the wider the better—a spoon, skim milk (unless you’re one of those 2%-loving savages*), and some kind of breakfast cereal with very small, granular pieces. If you plan it out far enough ahead of time, you can collect all the crumbs and shakies from the bottom of several boxes of cereal and combine them—that’s pretty much the perfect consistency for this experiment.
Gather your students ‘round, fill your bowl roughly halfway with your cereal bits, then slowly pour in your milk whilst stirring. (If any of your students can be trusted with such things, let them help.) You’re looking to create a mud-like consistency that will drip slowly off the spoon when tilted and held aloft. Once you’ve concocted your cerealmud, shake the bowl gently to smooth out the surface.
Select a few volunteers (NOT Kevin!) for this next part. With your bowl of cerealmud on a desk or tabletop, have your students take turns scooping up about a half-spoonful of the mixture, holding it about two feet above the bowl and then, very carefully, tipping the spoon so the goop drops onto the “mud” surface. Be sure that the kids spread their splatters across the whole area of the bowl to create craters in a variety of sizes and shapes. Observe and report!
As the cerealmud droplets hit the cerealmud surface in the bowl, it, of course, splatters, and the splattering splatter splats are, of course, pulled back down by gravity, strike the surface again—though with less force—and create additional mini-splatters of their own. Each splattering droplet creates a craterlike depression.
Here, the falling cerealmud is an analogue for meteorites striking the surface of the moon (or Mercury, if you prefer). These meteorite strikes produce immense amounts of heat, which melts the surface of the planet(oid), whatever it may be made of, turning it into a splattering liquid. The rate at which this liquid falls (creating additional mini-craters) affects the resulting crater patterns and formations. This rate is itself affected by the gravitational pull of the struck celestial body.
Mercury, having a greater gravitational pull than the Moon, has craters that are separate from each other, with smooth planes between them, as the splattered liquid returned to the surface quickly. The moon’s craters, because they were created by splattering liquid under far lighter gravity, are more spread out, have overlapping rims, and are separated by rough surface areas.
* No one actually drinks 1% milk.