Aug. 01, 2011

Make Craters with Mini-Meteors

by Bring Science Home

Bring Science Home: Activity 11

By Katherine Harmon
Scientific American's 'Bring Science Home' helps parents and teachers demonstrate that science is fascinating part of everyday life.

Key concepts
Gravity
Meteors
Plate tectonics

From National Science Education Standards: Earth's history

Introduction
The surface of the moon is full of jagged craters. This rough surface comes from millions of years of collisions with rocks—called meteors—that crash into its surface. Why doesn't Earth's surface look like that?

Earth's surface does have some evidence of meteorites, such as the massive Meteor Crater site in Arizona. That crater is about 4,000 feet (1,219 meters) across and about 570 feet (174 meters) deep. So does that mean that was the size and shape of the meteor that crashed there? Nope! It was much smaller than that. With this fun activity, you can use small snacks to study this striking feature of Earth's—and the moon's—surface.

Background
When you watch a meteor shower, most of the streaks of light (or "shooting stars") that you see are actually small rocks burning up in Earth's atmosphere. Most of them don't reach the ground, but those that do are called "meteorites." These rocks are traveling so fast (thousands of miles per hour) that they hit the ground with an amazing amount of force. That force is usually enough to move a lot more dirt than the size of the meteorite itself: the crater.

The meteorite that created the 4,000-foot-wide Meteor Crater in Arizona was probably only about 164 feet (50 meters) in diameter (really big for a rock falling from outer space, but still only a fraction of the size of the crater it created). Scientists estimate that this impact event occurred about 50,000 years ago—long before there were humans living in the area. The moon has a lot more visible impact craters because it doesn't have an atmosphere to burn up smaller incoming rocks. The moon also does not have liquid water or an active crust (with volcanoes and other forces) to alter the surface and remove evidence of past impacts. These agents helped to smooth out many of the meteorite craters here on Earth in the billions of years since the planet formed.

Materials
• Large shallow pan or tray with edges
• Flour
• Dry pudding mix, dry drink mix or cocoa powder or another powder that is a different color
• Roundish nuts, seeds and/or small fruits (such as raisins, almonds, peanut halves, cherries, and so on)
• Sifter or sieve

Preparation
• Fill the large pan or tray with an inch or two of flour.
• Cover that layer with a dusting of the second, different-colored powder using a sifter. This layer will be like the top level of "dirt" on the surface.
• Assemble your collection of mini "meteors."

Procedure
• Hold one of your mini meteors a couple feet above the flour tray. When the meteor falls, what do you think it will do to the surface?
• Drop the meteor (when it hits the surface, it becomes a meteorite). What happened?
What happens when the meteor falls faster? Try dropping it from a higher point—or carefully throwing it downward toward the flour surface.
• Now try different sized and shaped meteors. How are their craters different? How are they similar?
What does the pattern of "dirt" around your craters look like?

Observations and results
How did the size of the craters compare with the size of the meteorites that made them? Does a high-speed meteor make a different type of crater than a slow-speed meteor? Check both the size and shape.

The material that gets moved (or ejected) during the impact is known as "ejecta." By studying the patterns in which lower levels of dirt and rock were tossed up by the impact, scientists can make estimates about how big the meteorite originally was. (Meteors often get incinerated upon impact or disappear over time.) Ask a friend or your parent to make several craters and remove the meteorites; can you estimate the size of the meteorite from the ejecta and the crater?

Meteorites that survive their fall to the surface can also often tell us about where they came from by the type of rock and other chemicals they contain. For example, scientists have found some meteorites that are made up of the same material as the moon.

Why doesn't Earth's surface look like that of the moon? Aside from most of the rock burning up in the Earth's atmosphere before it can hit the surface, craters on Earth often vanish over time as the Earth's surface changes from the flow of liquid water, scraping glaciers, lava-spewing volcanoes or other agents. The moon doesn't have a very active surface, so meteor craters or even footprints from astronauts are likely to stay as they are for a very long time.

Share your mini meteorite strike observations and results! Leave a comment below or share your photos and feedback on Scientific American's Facebook page.

Cleanup
Be careful not to spill the powder when throwing it away.

More to explore
Why Are Impact Craters Always Round? from Scientific American
"Meteorite Nugget Pushes Back Age of the Solar System By Nearly 2 Million Years" from Scientific American
"Meteor Showers: Where, When and How to Look for Them" activity for kids from The Planetary Society
"Comets and Meteors" from the European Space Agency Kids
Comets, Meteors and Asteroids by Seymour Simon, ages 4–8
Meteors and Comets by Gregory Vogt, ages 9–12

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From ScientificAmerican.com (find the original story here); reprinted with permission. Scientific American is a trademark of Scientific American, Inc.

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