Big impact science: How do shooting stars become mega craters? This fun, Perseids project will use flour and some common objects to learn what can happen when meteors become meteorites. Image: George Retseck
Meteors and meteorites
Have you ever seen a "shooting star" race across the sky at night? Shooting stars are meteors zooming at high speed through Earth's atmosphere and burning up along the way from friction. And right now is one of the best times to see them in person. The Perseids, which are impressive meteor showers that happen each year from mid-July to late August, have their peak activity around August 11 to 14. They're caused by Earth traveling through debris from the Comet Swift-Tuttle. Luckily, most meteors are tiny and burn up before hitting the ground. But if a meteor doesn't disintegrate, what's its impact on Earth? In this activity you'll explore how a meteorite’s size is related to the size of the crater it makes on impact.
Craters are round, bowl-shaped depressions surrounded by a ring. They're made when a meteoroid in space collides with a planet, moon or other astronomical body. ("Meteorite" is what a meteor is called if it does not burn up before it lands. When a meteor is in space, it is known as a “meteoroid.”) Craters are what make our moon look like a ball of Swiss cheese. Each round hole is where a meteorite impacted the surface of the moon, so craters are often called "impact craters." Often, the meteorite that creates the crater explodes on impact, so only the crater is left as an empty reminder of the collision.
Moons and planets have been impacted by meteorites since the formation of our solar system. We see many craters on the moon because it doesn't have much of an atmosphere. An atmosphere (such as the one we have) often causes enough friction to make the falling rocks burn up. The moon, unlike Earth, also lacks weather and water features that eventually erode craters as well as tectonic activity to renew its surface. On Earth, however, there are only about 170 scientifically confirmed impact craters (others are thought to have existed but have been changed beyond recognition over time). And many of these confirmed craters are not obvious because they've been changed by geologic forces, eroded away, covered by sediment or are submerged underwater. Scientists have identified each crater by using several different kinds of clues, such as pieces of iron-rich meteorite or satellite imaging.
• Cardboard box, larger than a shoebox and fairly deep (Something like a small, movable box would be perfect.)
• About 10 pounds of flour
• Three different-size objects that are nearly spherical, such as a rubber bouncing ball, a baseball and a piece of roundish fruit (bigger than the baseball, such as a grapefruit). Smaller objects, such as marbles and beads, will not work well for this activity.
• Find a surface where the box is stable and you can comfortably drop the round objects from about two feet above the surface of the flour (once it is poured into the box). This workspace should also be easy to clean; some of the flour might end up on the surrounding surfaces.
• Slowly pour flour into the cardboard box. Shift the box from side to side to evenly distribute the flour. It should be a depth of at least two inches in your box. If there's not enough flour, you can either transfer the flour to a smaller box or add another bag of flour.
• Using a ruler, measure the diameter of one of your nearly spherical objects. These objects will serve as "meteorites" in this activity. What is the diameter of this object?
• Drop the meteorite from about two feet above the flour into flour by holding the object out at arm's length over the box and letting go. What happened when the meteorite hit the surface?
• Carefully remove the object from the flour—without disturbing the "crater" left behind. Then drop the same object into the flour box two more times, each time in a different spot in the box. Be sure to drop all of your meteorites the same way and from the same height.
• Now carefully measure the diameter of each of the three craters. (Do this by measuring the distance across the center of the depression in the flour.) What are the diameters of the craters? How do they compare with the diameter of the meteorite itself?
• Prepare your box for the next meteorite by shaking the box from side to side to even the flour until it is smooth and level.
• Measure the diameter of one of your other meteorites and drop it into the box of flour just as you did with the first meteorite. Drop it two more times to make three separate craters, as you did before (from the same height), and measure the diameter of each crater. What are the diameters of the craters? How do they compare with the diameter of the meteorite itself?
• Again prepare your box for the last meteorite by shaking the box from side to side to make the flour smooth and level.
• Measure the last meteorite's diameter and drop it into the flour box a total of three times, just as you did with the other two meteorites. Measure the diameter of these craters. What are the diameters of the craters? How do they compare with the diameter of the meteorite itself?
• What size craters did the smallest objects make? What size craters did the biggest ones make? In general, how do you think the diameter of a meteorite is related to the diameter of the crater it makes on impact?
• Extra: Do this activity again but this time pick only one of your "meteorites" and try dropping it from different heights. Does the height at which the meteorite is dropped affect the crater that forms?
• Extra: You could graph your results from this activity, plotting the average diameter of the crater on one axis and the diameter of the meteorite on the other axis. Do you notice any pattern between the size of the crater and the size of the meteorite, based on your graph?
• Extra: Repeat this activity using objects that are of similar sizes, but different in weight. How is a crater affected by the weight of the meteorite?