Our Battered Moon

Kathleen Damonte

You have probably heard the old tale about the Moon being made out of Swiss cheese because, to us on Earth, the Moon looks like it is full of holes. Those holes are actually impact craters, circular depressions that formed when objects, such as rocks that orbit the Sun, smashed into the surface of the Moon. In this month’s activity, you will have the opportunity to investigate how those craters formed.

How Craters Form

The Moon's Copernicus Crater (photo courtesy NASA)

Craters form when an object, such as a meteoroid, asteroid, or comet crashes into the rocky surface of a moon or planet, spraying out rocks, dust, and other ejecta. Ejecta is the material blasted from the surface upon impact. The heat energy from the impact is often hot enough to melt some of the surface material, giving the inside of the crater, or the floor, a compacted appearance. A raised edge called the rim forms around the edge of the crater from the material that is pushed upward and outward. Some craters have fine lines pointing away from them called rays that are created from ejecta thrown out of the crater at a high speed.

Craters Everywhere

One of the most famous craters on the Moon is named Copernicus. It is well known because of its large size and many rays. It was formed nearly one billion years ago, is 93 km across (66 miles), and was named for Nicolaus Copernicus, a Polish astronomer who lived from 1473 to 1543. Copernicus is on the side of the Moon facing Earth and can be viewed using binoculars. The next time you observe the Moon, see if you can find this crater.

Craters are found not only on the Moon but on all of the “rocky” planets: Mercury, Venus, and Mars. Many of the moons of the giant planets of the outer solar system also show impact craters. There are even impact craters on Earth. One of the largest and most well known craters is the Barringer Meteorite Crater in the Arizona desert. This crater is nearly a mile wide (1.6 km) and is 570 feet deep (174 m). Most of the impact craters on Earth are not very noticeable. Comparing craters on Earth and other celestial bodies is a great way to explore the effects of wind and water and the geologic activity that have taken place on Earth.

To learn more about the Moon and impact craters visit the following websites:
Zoom Astronomy
www.enchantedlearning.com/subjects/astronomy
Earth Impact Database
www.unb.ca/passc/ImpactDatabase/index.html
Meteors, Meteorites, and Impacts
www.nineplanets.org/meteorites.html

Now try this classic classroom activity to make your own impact craters.

Create a Crater

Materials:

• Large plastic, metal, or cardboard pan or box (aluminum roasting pans work well)
• Bag of white flour
• 3 rocks of different sizes and masses
• ½ cup instant chocolate-milk powder or sweetened-drink powder
• Old newspaper
• Plastic or metal spatula
• Ruler or tape measure
• Balance scale
• Safety goggles*

Note: You can also use different sized steel balls and then use a magnet to extract the “meteorites” without disturbing the craters.

*Safety goggles prevent the colored powder from getting in students’ eyes.

In this activity, you will make a crater by dropping a rock onto a flour surface that will be like the surface of the Moon. You will find out if the mass of the falling object has an effect on the size of the crater that is created.

Directions:

1. Put on your safety goggles and spread out newspaper on the floor or table to catch any spills.
2. Place the box or pan on the newspaper and fill with flour. The flour needs to be at least 8 cm deep in the box or pan.
3. Smooth the surface of the flour with the spatula.
4. Sprinkle a thin layer of the colored powder on top of the flour. (This will help you see the crater that is created.)
5. On a balance scale, find the mass of the three rocks.
6. Drop the rock with the least mass from a height of one meter above the pan.
7. Use the ruler or tape measure to measure the diameter (distance across) of the crater. Record the diameter on the chart.
8. Smooth the flour down again with the spatula and add more colored powder to prepare the surface for another drop.
9. Repeat steps 6–7 with the other two rocks (in order of increasing mass), dropping them from the same height you dropped the first rock.

Questions:

1. Which rock created the larger crater? Why?
2. What does this activity tell you about the object that hit the Moon’s surface to create a large crater like Copernicus? How do you know?

Extensions:

• Have students illustrate the craters after each drop and label the parts of the crater created.
• Create a graph that shows the relationship between the mass of the rock and the diameter of the crater.
• Try dropping rocks from different heights and angles. Include this information in a revised data table.

Kathleen Damonte teaches seventh-grade science at Julius West Middle School in Rockville, Maryland.

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