Scratching the Surface - Crater Creations
In the 30-45 minute Crater Creations activity, teams of children ages 8-13, experiment to create impact craters and examine the associated features. The children observe images of Martian craters and explore how the mass, shape, velocity, and angle of impactors affects the size and shape of the crater.
This activity has been modified from Lava Layering, an activity in Exploring the Moon: a Teacher's Guide with activities for Earth and Space Sciences, NASA Education Product EG-1997-10-116-HQ by J. Taylor and L. Martel.
What's the Point?
- Impact craters are caused when an impactor collides with a planet.
- A crater's size and features depend on the mass, velocity, and incoming angle of the impactor.
- Impact craters provide insights into the age and geology of a planet's surface.
- Models — such as the children are using here — can be tools for understanding the natural world
- Geologists use features on Earth to help them understand how similar features may have formed on other planets, like Mars.
For each child:
For each team of 4–8 children:
- A large pan or box such as a dish pan, aluminum baking pan, or copy paper box lid, (larger pans allow children to drop more impactors before having to re-smooth or resurface)
- Enough sand, sugar, rice, or oatmeal to fill the pan about 4 inches
- Enough flour to make a 1" to 2" deep layer
- 1 heaping cup of powdered cocoa
- A sifter
- A large trash bag or piece of cloth or plastic to place under the crater box
- Several objects that can be used as impactors, such as large and small marbles, golf balls, rocks, bouncy balls, and ball bearings. Use your imagination!
- Paper and pencil
- Images of craters from the Setting the Scene activity
- Safety glasses
For the Facilitator:
- Prepare an area large enough to accommodate the crater boxes for the number of teams participating. Allow several feet between each box.
- Prepare the appropriate number of crater boxes
1. Introduce the activity by asking the children what they think will happen when an impactor — a heavy object — is dropped into one of the boxes.
2. Divide the children into groups of 3 to 5 and have each group stand by a box. Invite them to begin experimenting by having them select one impactor to drop and determining from what height they will drop it (encourage them to not throw their impactor). What do they think will happen? Have each teams drop their impactor one at a time.
- What do they observe?
- Does the feature that was created look like any of the features they observed on the surface of Mars or Earth?
- Which features? Craters — roughly circular depressions on the surface of a planet.
- How are they similar? Different? Some similarities include the circular shape and depression, and the material that is excavated from the crater and forms a rim — the ejecta. Some differences include the fact that the impactor is still present in the model. Long bright streaks — rays — probably extend out from the crater they created; these also occur in some places on Mars and the Moon.
After each crater creation, ask them to carefully remove their impactor, to make the crater clearly visible (in reality, impactors are completely — or almost completely — obliterated upon impact; any remains of the impactor are called "meteorites").
3. Now, taking turns, let the children experiment with creating craters! Have each group conduct an experiment by changing one variable to see how it affects impact crater size. Experiments could explore different impactor sizes, weights, distances dropped, or angles of impact. For example, one group could drop the same impactor from different heights (modeling different velocities of the incoming impactors), and another group could experiment by dropping different sized impactors from the same height. If the children want to experiment with angles of impact they will need to throw the impactors at the box; caution should be used to make sure no one is standing on the opposite side of the box in case the impactor misses. Invite the children to predict what will happen in their experiment. Have the children measure the width and depth of each impact crater formed in their experiment.
- What did the groups observe?
- How did the weight of objects affect the size and depth of the crater you created?
- How did the size of the object affect the size and depth of the crater?
- How did dropping or throwing the impactors from different heights affect the size and depth of the craters they formed?
Have the children reflect on what they observed and the images from Mars and Earth. Invite them to record what they learned in their GSI Journals.
- What features did the children create in their models? Impact craters.
- Do similarly shaped features occur on Mars or Earth? Yes, both.
- How are they different? The craters on Mars are much, much larger.
- How do the children think the craters on Mars and Earth formed? By large impactors — asteroids or comets — striking the Earth and Mars.
- Scientists have not actually seen any large asteroids or comets hit Mars, but they think the large craters on Mars — and on other planets and moons — were created by them. Scientists have observed very small asteroids hitting Earth and several pieces of Comet Shoemaker-Levy struck Jupiter. When the children see "shooting stars" — more accurately called "meteors" — they are seeing tiny dust to sand-sized "asteroids" that are streaking toward Earth's surface. They are too small to make craters or leave any meteorites to collect.
- What evidence might scientists have to make them think impactors created these craters? Scientists experiment with models — like the children did — to determine what type of feature an impactor might leave behind. They also have other evidence from some craters on Earth — like fragments of the asteroid (meteorites), or alterations to the rocks and minerals at the impact site caused by the impactor striking the ground at high speed.
Invite the children to reflect on what they learned during all of their different investigations.
- How might observations on Earth help scientists interpret what they see on other planets? Scientists study features — like volcanos — on Earth to understand their shape and size, what they are made of, and how they form. On Earth, this information can be used to predict where volcanos may form, and when they may erupt. By understanding volcanos on Earth, scientists can interpret what they see on other planets. If they see a feature that is similar in shape and detail to volcanos on Earth, even if the volcano is not erupting, they can interpret that it is a volcano — and this tells them about the history of the planet.
- How might relying on Earth observations not be a good model for scientists to use when studying other planets? Other planets may have characteristics that are not the same as on Earth. Titan, the large moon of Saturn, has features that look like river channels, but these were carved by liquid methane — not water!
If things might be different, why not stop trying to understand other planets until we can go there? First, what's the fun of that? And second, it may be a long time until we get there! Planetary geology is about creating a picture of what it is like on a planet and how it has changed over time. Geologists use every piece of evidence they can — images from telescopes and spacecraft, information from rovers — to help them paint this picture. As they get more information, they alter the picture to fit the evidence. By studying what is available, scientists can help to identify the important questions that we should address in future robotic and human missions! And by understanding how planets change — and why — we can better understand how Earth has and will change. Learning about the history of water on Mars can tell us more about our own future.
February 4, 2010